Abstract
Introduction:
Breastfeeding is recommended. It is unknown whether preconception or prenatal cannabis use are related to breastfeeding behaviors.
Methods:
This population-based retrospective cohort study included 200,207 pregnancies in Northern California (2016–2022) with live births screened in early pregnancy for cannabis use. Exposures included prenatal cannabis use, preconception cannabis use only, or no cannabis use. Additional analyses considered frequency of prenatal cannabis use. Longitudinal breastfeeding outcomes assessed at each well-child visit during the first year included any breastfeeding, and full breastfeeding (breastmilk without formula). Adjusted prevalence ratios (aPRs) were calculated using modified Poisson regression for longitudinal binary outcomes in 2024 and 2025. The risk of stopping breastfeeding among those who started was modeled using Cox proportional hazard regression.
Results:
Overall, 7.6% of pregnancies had preconception cannabis use only and 7.2% had prenatal use. Most people (94.6% overall) initiated breastfeeding, with only modest differences by cannabis use (94.9% no cannabis use, 95.7% preconception cannabis use only, 90.5% prenatal cannabis use). However, over time, prenatal cannabis use was associated with earlier discontinuation of breastfeeding (aHR 1.12, 95% CI: 1.09–1.15) and lower prevalence of breastfeeding (aPR 0.84, 95% CI: 0.82–0.85 at 6 months, aPR 0.81, 95%CI: 0.78–0.83 at 12 months). Associations were stronger for higher frequency use. There were small differences in breastfeeding among those with preconception cannabis use only verses none. Full breastfeeding results were similar.
Conclusions:
Despite high prevalence of breastfeeding initiation, prenatal cannabis use was associated with earlier breastfeeding discontinuation and lower prevalence at 6 and 12 months.
INTRODUCTION
Rates of cannabis use during pregnancy have risen in recent years,1,2 with 7.9% of pregnant individuals in the US reporting past-month cannabis use in 2022.3 While some pregnant individuals decrease or discontinue cannabis use,4,5 many return to use postpartum.6–9 Research shows that postpartum cannabis use is driven by recreational use, self-medication for depression, anxiety, or chronic pain, and coping with the stresses of parenting a newborn.10–12
The desire to use cannabis may influence decisions about initiating or continuing breastfeeding.11 Breastfeeding is recommended for at least 2 years, with full breastfeeding (breastmilk without formula use) recommended through 6 months.13 Delta-9-tetrahydrocannabinol (THC) exposure via breastmilk has been associated with less frequent and shorter feedings, infant lethargy, and growth delays.14 However, the short- and long-term health effects of cannabis exposure through breast milk remain unclear, and the few existing studies provide conflicting evidence.6,9,15,16 Due to potential risks, national medical guidelines advise against cannabis use during lactation,17–19 yet, studies indicate that 5–18% of breastfeeding individuals use cannabis.20,21 Initial findings on the association between postpartum cannabis use and breastfeeding duration are inconsistent,4,7,22 and it is unknown whether preconception or prenatal cannabis use are risk factors for lower breastfeeding initiation and earlier discontinuation.
Identifying preventable preconception and prenatal risk factors for not breastfeeding or early breastfeeding discontinuation is critical for early detection and development of targeted education and intervention strategies. In this large retrospective cohort study, the association between preconception and prenatal cannabis use and breastfeeding initiation and continuation was examined among individuals in a healthcare system with universal prenatal screening for cannabis use by self-report and urine toxicology testing.
METHODS
Study Sample
Kaiser Permanente Northern California (KPNC) is a comprehensive healthcare system serving 4.6 million patients, representative of the insured population in Northern California.23 IRB approval was secured from KPNC, including a waiver for consent and HIPAA authorization, and the State of California (governing the use of birth certificate data).
This population-based retrospective cohort study included singleton pregnancies that resulted in a live birth between 1/1/2016–12/31/2022. Eligibility criteria (Appendix Figure 1) included any KPNC membership during pregnancy and ≥1 prenatal visit. Pregnancies were required to have a non-missing self-reported breastfeeding question within the month after delivery, a response to the questions about preconception and prenatal cannabis use, and a prenatal urine toxicology test for cannabis to be included. Infants born <37 weeks gestation or admitted to the neonatal intensive care unit were excluded.
Measures
Measures were extracted from KPNC administrative and electronic health record (EHR) data and California birth certificate data.
Self-reported preconception and prenatal cannabis use were assessed at entrance to prenatal care (~7–10 weeks gestation) using a self-administered questionnaire assessing frequency of cannabis use in the year before pregnancy and during pregnancy (daily, weekly, monthly or less, and none). Individuals consented to and completed a toxicology test at entrance to prenatal care. A confirmatory test for the cannabis metabolite, 11-nor-9-carboxy-delta-9-tetrahydrocannabinol—detectable for up to ~30 days after last use in regular users—was performed on positive immunoassay results using liquid chromatography-tandem mass spectrometry. The primary exposure was defined as mutually exclusive categories for preconception cannabis use only (self-reported use in the year before pregnancy and no prenatal use), prenatal cannabis use (by either self-report or positive toxicology test), or none. For frequency of prenatal cannabis use, we added a category for those with a positive toxicology test who did not self-report use (i.e., unknown frequency).
Breastfeeding was assessed at regularly scheduled outpatient well-child visits at birth-to-1 week (≤ 13 days after birth), 2-to-4 weeks (14–40 days), 2 months (41–99 days), 4 months (100–159 days), 6 months (160–240 days), 9-to-10 months (241–345 days), and 12 months (346–425 days). The responses for birth-to-1 week and 2-to-4 weeks were combined to create an initial breastfeeding status for the first month (i.e., birth-to-1-month visit). For visits prior to 12 months, parents were asked, “What does your child eat” with 3 possible responses: only breast milk, only formula, or some breast milk and some formula. At 12 months, parents were asked the same question but could select all that apply from breast milk, formula, cow’s milk, and solid foods. Any breastfeeding through 12 months was defined as feeding breastmilk regardless of other foods or liquids. Full breastfeeding through 6 months was defined as feeding breastmilk without formula; solid foods are not recommended prior to 6 months.
Data on maternal age at pregnancy onset, self-reported race and ethnicity (Hispanic and non-Hispanic Asian, Black, White, and American Indian/Alaska Native/Pacific Islander/multiracial/unknown; included as a social construct due to known differences in the prevalence of prenatal cannabis use by race and ethnicity), maternal insurance (Medicaid/Medicare vs. other), neighborhood deprivation index (quartiles),24 and pre-pregnancy BMI categories (BMI = kg/m2; underweight<18.5, normal-18.5–24.9, overweight-25.0–29.9, obese ≥30.0) were extracted from the EHR. Maternal education (high school or less, some college, college graduate, graduate school, unknown) was ascertained from birth certificates. Parity (0, 1, ≥2) was ascertained from EHR and birth certificate data. Month of prenatal care initiation was classified using the Kotelchuck initiation index: inadequate (7+), intermediate (5–6), adequate (3–4), or adequate plus (1–2).25 Non-cannabis prenatal substance use was based on universal screening at entrance to prenatal care and defined as prenatal use of alcohol, nicotine, or other substances (opioids, stimulants, and anxiety/sleep medications), as described in the Appendix Methods and in previous work.26
Statistical Analysis
We fit extended modified Poisson models for longitudinal binary data with robust standard errors using the extension of the sandwich variance estimator to account for the nested correlation in the outcomes for repeated breastfeeding measurements per infant (one per scheduled visit) and multiple pregnancies per person.27 Crude and adjusted prevalence ratios (aPRs) with 95% CIs were calculated. We performed a test for trend by converting the frequency variable into a continuous variable and including it in the modified Poisson model. Adjusted models included covariates listed above.
Among those who reported breastfeeding at the initial visit, we estimated differences by cannabis use in the average probability of stopping breastfeeding using a Cox proportional hazards (PH) model. The PH assumption was examined using interaction terms with log time; if any departures from the assumption were detected, we reported the time-varying hazard ratios (HRs) of the exposure using interaction terms for the time period at each visit. We report crude and adjusted hazard ratios (aHRs) with 95% CIs and direct adjusted survival curves.
Analyses were conducted using SAS 9.4. Two-sided P-values <.05 were considered statistically significant.
RESULTS
The maternal characteristics of the 200,207 pregnancies (from 170,591 unique individuals) were 27.2% Hispanic, 26.4% Asian, 5.8% Black, 36.3% White, mean (SD) age was 31.1 (5.2) years, and 10.9% were insured by Medicaid or Medicare. Overall, 7.2% screened positive for prenatal cannabis use (1.4% were positive by self-report only, 3.8% were positive by toxicology testing only, and 2.0% were positive by both); an additional 7.6% screened positive for preconception cannabis use (without prenatal use). Self-report and toxicology testing were completed at a median 7.6 weeks (Q1-Q3:5.9–9.4) and 8.9 weeks (Q1-Q3:7.7–11.3) of gestation, respectively. Prenatal cannabis use frequency was 1.7% monthly or less, 0.8% weekly, 0.8% daily, and 3.8% had a positive toxicology test but no self-reported use (Table 1). Prenatal cannabis use differed by sociodemographics (Appendix Table 1). Of the 170,591 unique individuals, 84% contributed one pregnancy, 15% two pregnancies, and 1% 3–5 pregnancies.
Table 1.
Pregnancy and Maternal Characteristics, Overall and by Breastfeeding Status
| N (Row %) | |||||
|---|---|---|---|---|---|
| Any breastfeeding at the birth–to-1-month visit (n=200,207) |
Any breastfeeding at the 12-month visit (n=146,579) |
||||
| Overall N (Col%) N=200,207 |
No N=10,767 (5.4%) |
No N=86,972 (59.3%) |
|||
| Age | |||||
| Mean (SD), years | 31.1 (5.2) | 30.1 (5.8) | 31.1 (5.1) | ||
| Categories | |||||
| <18 years | 1,015 (0.5) | 128 (12.6) | 390 (78.6) | ||
| 18–24 years | 24,828 (12.4) | 2,098 (8.5) | 10,225 (70.9) | ||
| 25–30 years | 54,131 (27.0) | 3,049 (5.6) | 24,106 (62.3) | ||
| 31–35 years | 75,093 (37.5) | 3,199 (4.3) | 32,840 (56.7) | ||
| 36+ years | 45,140 (22.5) | 2,293 (5.1) | 19,411 (55.4) | ||
| Race and ethnicity | |||||
| Hispanic | 54,371 (27.2) | 3,986 (7.3) | 24,387 (66.0) | ||
| Non-Hispanic | |||||
| Asian | 52,760 (26.4) | 2,119 (4.0) | 24,191 (58.0) | ||
| Black | 11,659 (5.8) | 1,080 (9.3) | 4,833 (65.0) | ||
| White | 72,702 (36.3) | 3,129 (4.3) | 30,022 (55.2) | ||
| Other and unknowna | 8,715 (4.4) | 453 (5.2) | 3,539 (57.8) | ||
| Education | |||||
| High school or less | 31,525 (15.7) | 3,566 (11.3) | 14,081 (72.0) | ||
| Some college | 57,885 (28.9) | 4,029 (7.0) | 26,295 (66.2) | ||
| College graduate | 62,599 (31.3) | 1,944 (3.1) | 27,573 (55.9) | ||
| Graduate school | 40,920 (20.4) | 832 (2.0) | 16,097 (48.7) | ||
| Unknown | 7,278 (3.6) | 396 (5.4) | 2,926 (59.8) | ||
| Insurance type | |||||
| Medicaid or Medicare | 21,846 (10.9) | 2,132 (9.8) | 9,817 (66.2) | ||
| Other | 178,361 (89.1) | 8,635 (4.8) | 77,155 (58.6) | ||
| Neighborhood deprivation index | |||||
| Q1 - Least deprivation | 36,769 (18.4) | 978 (2.7) | 14,850 (52.1) | ||
| Q2 | 58,236 (29.1) | 2,398 (4.1) | 24,987 (56.3) | ||
| Q3 | 57,825 (28.9) | 3,322 (5.7) | 25,584 (61.3) | ||
| Q4 - Most deprivation | 47,353 (23.7) | 4,069 (8.6) | 21,537 (67.4) | ||
| Pre-pregnancy body mass index categories | |||||
| Underweight | 4,387 (2.2) | 205 (4.7) | 1,786 (55.9) | ||
| Normal | 88,788 (44.3) | 3,334 (3.8) | 35,803 (54.3) | ||
| Overweight | 55,839 (27.9) | 3,015 (5.4) | 24,618 (60.1) | ||
| Obese | 51,193 (25.6) | 4,213 (8.2) | 24,765 (68.0) | ||
| Lived with partner | |||||
| Yes | 159,771 (79.8) | 8,171 (5.1) | 69,214 (58.7) | ||
| No | 11,767 (5.9) | 1,183 (10.1) | 5,196 (72.6) | ||
| Unknown | 28,669 (14.3) | 1,413 (4.9) | 12,562 (58.2) | ||
| Parity | |||||
| 0 | 89,018 (44.5) | 3,495 (3.9) | 41,412 (60.7) | ||
| 1 | 70,978 (35.5) | 3,706 (5.2) | 30,018 (57.9) | ||
| 2+ | 40,211 (20.1) | 3,566 (8.9) | 15,542 (58.6) | ||
| Kotelchuck Month of Initiation Index | |||||
| Adequate plus | 127,939 (63.9) | 6,566 (5.1) | 57,093 (59.0) | ||
| Adequate | 61,310 (30.6) | 3,401 (5.5) | 25,854 (59.5) | ||
| Intermediate | 6,294 (3.1) | 455 (7.2) | 2,363 (63.4) | ||
| Inadequate | 4,664 (2.3) | 345 (7.4) | 1,662 (61.9) | ||
| Substance use in pregnancy | |||||
| Alcohol | 18,987 (9.5) | 752 (4.0) | 8,298 (57.4) | ||
| Nicotine | 6,763 (3.4) | 767 (11.3) | 3,202 (73.5) | ||
| Otherb | 8,912 (4.5) | 753 (8.4) | 4,172 (66.8) | ||
| Cannabis use | |||||
| None | 170,494 (85.2) | 8,741 (5.1) | 74,177 (58.5) | ||
| Preconception use only | 15,294 (7.6) | 661 (4.3) | 6,690 (59.7) | ||
| Prenatal use | 14,419 (7.2) | 1,365 (9.5) | 6,105 (70.7) | ||
| Frequency of prenatal cannabis use | |||||
| None | 185,788 (92.8) | 9,402 (5.1) | 80,867 (58.6) | ||
| Monthly or less | 3,414 (1.7) | 246 (7.2) | 1,452 (68.0) | ||
| Weekly | 1,677 (0.8) | 152 (9.1) | 685 (69.2) | ||
| Daily | 1,687 (0.8) | 181 (10.7) | 748 (70.8) | ||
| Unknownc | 7,641 (3.8) | 786 (10.3) | 3,220 (72.3) | ||
N=170,591 unique pregnant individuals;142,853 (84%) contributed one pregnancy, 25,946 (15%) two pregnancies, and 1,792 (1%) three to five pregnancies
Other race includes multiracial, Pacific Islander, Hawaiian Native, Native American, and Alaska Native.
Other prenatal substance use includes opioids, stimulants, and/or anxiety/sleep medications.
Unknown frequency represents individuals who did not disclose prenatal cannabis use but had a positive toxicology test.
Breastfeeding status was available by visit as follows: birth-to-1 month (n=200,207), 2 months (n=177,312), 4 months (n=167,827), 6 months (n=165,524), 9-to-10 months (n=71,056), and 12 months (n=146,579) (Figure 1, Appendix Table 2). Overall, 94.6% of the cohort initiated any breastfeeding, recorded at the birth-to-1-month visit. Crude breastfeeding initiation rates were highest among those with only preconception cannabis use (95.7%), followed by those with no cannabis use (94.9%) and prenatal use (90.5%). Although the crude prevalence ratio indicated a slightly lower prevalence of breastfeeding initiation among those with prenatal cannabis use vs. no use (PR=0.95;95%CI:0.95–0.96; Appendix Table 3), in the fully adjusted model prenatal cannabis use vs. no use was associated with a higher adjusted prevalence of any breastfeeding at the birth-to-1-month-visit (aPR=1.09;95%CI:1.09–1.10; Table 2).
Figure 1. Prevalence of Any and Full Breastfeeding, by Preconception and Prenatal Cannabis Use and Frequency of Prenatal Cannabis Use.
Notes. Sample by visit: birth-to-1 month (n=200,207), 2 months (n=177,312), 4 months (n=167,827), 6 months (n=165,524), 9–10 months (n=71,056), and 12 months (n=146,579). Prevalence data are presented in tabular form in eTables 2 and 4
Table 2.
Adjusted Prevalence Ratios of Breastfeeding by Preconception and Prenatal Cannabis Use
| Prevalence ratios (PRs) and 95% confidence intervals (CIs) | ||||||
|---|---|---|---|---|---|---|
| Cannabis use (reference=none) |
Frequency of prenatal cannabis use (reference = none) |
|||||
| Preconception only | Prenatal | Monthly or less | Weekly | Daily | Unknown | |
| Any breastfeeding | ||||||
| Adjusted average PRa | 1.02 (1.01–1.03) | 0.94 (0.93–0.95) | 0.97 (0.95–0.99) | 0.96 (0.93–0.99) | 0.96 (0.93–0.99) | 0.92 (0.91–0.93) |
| Adjusted PR, by visita | ||||||
| Birth-to-1-month | 1.03 (1.03–1.03) | 1.09 (1.09–1.10) | 1.08 (1.07–1.09) | 1.09 (1.07–1.11) | 1.11 (1.09–1.13) | 1.09 (1.08–1.10) |
| 2-month | 1.02 (1.01–1.03) | 0.95 (0.94–0.96) | 0.99 (0.97–1.01) | 0.98 (0.94–1.01) | 0.96 (0.93–1.00) | 0.92 (0.90–0.94) |
| 4-month | 1.02 (1.01–1.03) | 0.88 (0.86–0.89) | 0.93 (0.90–0.96) | 0.89 (0.85–0.93) | 0.89 (0.85–0.94) | 0.84 (0.82–0.86) |
| 6-month | 1.01 (1.00–1.02) | 0.84 (0.82–0.85) | 0.89 (0.86–0.92) | 0.86 (0.81–0.90) | 0.85 (0.81–0.90) | 0.80 (0.78–0.82) |
| 9–10-month | 1.01 (0.99–1.04) | 0.82 (0.79–0.85) | 0.86 (0.81–0.92) | 0.90 (0.82–0.99) | 0.79 (0.71–0.88) | 0.79 (0.75–0.83) |
| 12-month | 0.99 (0.96–1.01) | 0.81 (0.78–0.83) | 0.85 (0.80–0.90) | 0.84 (0.76–0.92) | 0.83 (0.76–0.91) | 0.77 (0.74–0.81) |
| Full breastfeeding | ||||||
| Adjusted average PRa | 1.06 (1.05–1.07) | 0.97 (0.96–0.99) | 0.99 (0.96–1.02) | 0.99 (0.95–1.03) | 0.97 (0.93–1.02) | 0.95 (0.92–0.97) |
| Adjusted PR, by visita | ||||||
| Birth-to-1-month | 1.11 (1.10–1.12) | 1.15 (1.13–1.16) | 1.12 (1.09–1.15) | 1.16 (1.12–1.20) | 1.17 (1.13–1.21) | 1.13 (1.11–1.15) |
| 2-month | 1.06 (1.04–1.08) | 0.91 (0.89–0.93) | 0.95 (0.91–0.98) | 0.96 (0.91–1.01) | 0.89 (0.84–0.95) | 0.87 (0.84–0.89) |
| 4-month | 1.03 (1.01–1.04) | 0.84 (0.82–0.87) | 0.91 (0.87–0.96) | 0.88 (0.83–0.95) | 0.83 (0.77–0.89) | 0.80 (0.77–0.83) |
| 6-month | 1.00 (0.98–1.02) | 0.84 (0.81–0.86) | 0.87 (0.83–0.92) | 0.80 (0.74–0.87) | 0.82 (0.75–0.90) | 0.83 (0.80–0.86) |
Adjusted for maternal age, education, race and ethnicity, and neighborhood deprivation index, Medicaid/Medicare coverage, parity, residing with partner, pre-pregnancy BMI, Kotelchuck month of prenatal care initiation index, alcohol use in pregnancy, nicotine use in pregnancy, and other prenatal substance use (anxiety medication, sleep medication, opioids, or stimulants).
Unknown frequency represents individuals who did not disclose prenatal cannabis use but had a positive toxicology test.
Bold indicates P < .05.
Note. Sample by visit: birth-to-1 month (n=200,207), 2 months (n=177,312), 4 months (n=167,827), 6 months (n=165,524), 9–10 months (n=71,056), and 12 months (n=146,579).
The similarity in the prevalence of breastfeeding by prenatal cannabis use vs no cannabis use changed starting at 2 months when 83.2% of those with no cannabis use but only 69.0% of those with prenatal cannabis use continued to breastfeed (aPR=0.95;95%CI:0.94–0.96). This trend continued through 12 months, when breastfeeding prevalence was 41.5% among those with no cannabis use but only 29.3% for prenatal cannabis use (aPR=0.81;95%CI:0.78–0.83).
Similarly, the Cox PH model found that among those who initiated breastfeeding, the average adjusted risk of stopping breastfeeding during the first year was higher among those with prenatal cannabis vs. no use (aHR=1.12;95%CI:1.09–1.15) (Table 3, Appendix Figure 2). Notably, there was a departure from the PH assumption (P<.001), meaning that the risk of stopping varied over the first year. Those with prenatal cannabis use were more likely to stop breastfeeding in the early months, with the greatest increased risk for stopping occurring at 2 months (aHR=11.13;95%CI:10.8–11.5, vs. no use). Those with prenatal cannabis use continued to be at increased risk for stopping at 4 months (aHR=3.77;95%CI:3.65–3.88) and 6 months (aHR=1.60;95%CI:1.54–1.67). In contrast, throughout the first year, the prevalence of breastfeeding among those with only preconception cannabis use remained similar to those with no cannabis use (aPR=1.02;95%CI:1.01–1.03;Table 2). Those with only preconception cannabis use had a slightly higher prevalence of breastfeeding at the birth-to-1-month visit (aPR=1.03;95%CI:1.03–1.03), but a greater risk of stopping in months 2–9 among those who initiated breastfeeding, leading to no difference in prevalence at 12-months (aPR=0.99;95%CI:0.96–1.01) compared to those with no cannabis use.
Table 3:
Hazard Ratios (HRs) of Stopping Breastfeeding Among Those Who Initiated, by Preconception and Prenatal Cannabis Use and Frequency of Prenatal Cannabis Use
| Preconception only and prenatal use (reference=none) |
Frequency of prenatal cannabis use (reference = none) |
|||||
|---|---|---|---|---|---|---|
| Preconception cannabis use only | Prenatal cannabis use | Monthly or less | Weekly | Daily | Unknownb | |
| Stop any breastfeeding (n=189,440) | ||||||
| Crude average HR | 1.07 (1.05–1.10) | 1.49 (1.45–1.53) | 1.34 (1.27–1.41) | 1.43 (1.33–1.54) | 1.50 (1.39–1.62) | 1.57 (1.51–1.63) |
| Adjusted average HRa | 0.99 (0.97–1.02) | 1.12 (1.09–1.15) | 1.07 (1.01–1.13) | 1.09 (1.01–1.17) | 1.04 (0.96–1.13) | 1.17 (1.13–1.22) |
| Adjusted HR, by visita | ||||||
| 2-month visit | 12.28 (11.8–12.8) | 11.13 (10.8–11.5) | 9.28 (8.71–9.88) | 8.34 (7.72–9.02) | 9.20 (8.47–10.0) | 9.66 (9.28–10.05) |
| 4-month visit | 4.21 (4.08–4.34) | 3.77 (3.65–3.88) | 3.35 (3.18–3.56) | 3.37 (3.13–3.63) | 3.26 (3.02–3.52) | 3.41 (3.28–3.54) |
| 6-month visit | 1.85 (1.78–1.93) | 1.60 (1.54–1.67) | 1.62 (1.50–1.75) | 1.62 (1.45–1.81) | 1.51 (1.36–1.68) | 1.41 (1.34–1.50) |
| 9–10-month visit | 1.54 (1.58–1.61) | 1.21 (1.14–1.28) | 1.21 (1.09–1.34) | 1.12 (0.95–1.33) | 1.19 (1.03–1.37) | 1.12 (1.04–1.21) |
| 12-month visit | 0.41 (0.40–0.43) | 0.33 (0.32–0.35) | 0.37 (0.34–0.40) | 0.35 (0.31–0.40) | 0.29 (0.26–0.33) | 0.32 (0.30–0.34) |
| Stop full breastfeeding (n=137,598) | ||||||
| Crude average HR | 1.14 (1.11–1.17) | 1.52 (1.48–1.57) | 1.39 (1.32–1.48) | 1.50 (1.39–1.62) | 1.58 (1.45–1.71) | 1.54 (1.48–1.61) |
| Adjusted average HRa | 1.03 (1.00–1.06) | 1.13 (1.09–1.17) | 1.08 (1.02–1.15) | 1.11 (1.03–1.21) | 1.08 (0.99–1.18) | 1.16 (1.11–1.21) |
| Adjusted PR, by visita | ||||||
| 2-month visit | 6.26 (6.06–6.45) | 5.27 (5.11–5.44) | 4.68 (4.43–4.95) | 4.26 (3.96–4.58) | 4.54 (4.23–4.86) | 4.76 (4.59–4.93) |
| 4-month visit | 2.07 (2.00–2.14) | 1.76 (1.70–1.83) | 1.55 (1.43–1.67) | 1.53 (1.37–1.69) | 1.64 (1.50–1.78) | 1.71 (1.63–1.80) |
| 6-month visit | 0.32 (0.30–0.33) | 0.28 (0.26–0.30) | 0.30 (0.26–0.33) | 0.35 (0.30–0.41) | 0.26 (0.22–0.31) | 0.25 (0.23–0.28) |
Cox proportional hazard model adjusted for maternal age, education, race and ethnicity, and neighborhood deprivation index, Medicaid/Medicare coverage, parity, residing with partner, pre-pregnancy BMI, Kotelchuck month of prenatal care initiation index, alcohol use in pregnancy, nicotine use in pregnancy, and other prenatal substance use (anxiety medication, sleep medication, opioids, or stimulants).
Unknown frequency represents individuals who did not disclose prenatal cannabis use but had a positive toxicology test.
Bold indicates P < .05.
The results for full breastfeeding were similar to the results for any breastfeeding. Full breastfeeding initiation was highest among those with preconception use only (74.5%), followed by those with no cannabis use (68.4%) and those with prenatal use (66.3%). In fully adjusted models, prenatal cannabis use (vs. no use) was associated with a higher prevalence of full breastfeeding at the birth-to-1-month visit compared to no cannabis use (aPR=1.15;95%CI:1.13–1.16; Table 2). However, the Cox PH model found that among those who initiated full breastfeeding, the average adjusted risk of stopping full breastfeeding during the first year was higher among those with prenatal cannabis vs. no use. As a result, at 6 months, full breastfeeding prevalence was 42.7% among those with no cannabis use and only 30.3% among those with prenatal use (aPR=0.84;95%CI:0.81–0.86).
Compared to those with no cannabis use, those with only preconception cannabis use had greater prevalence of full breastfeeding averaged over the first 6 months (aPR=1.06;95%CI,1.05–1.07), due to a higher prevalence at birth-to-1 month and 2 months. However, the Cox PH model found that among those who initiated full breastfeeding, the average adjusted risk of stopping full breastfeeding during months 2–6 was higher among those with preconception cannabis use only vs. no use, leading to no difference in prevalence at 6-months (aPR=1.00 95%CI:0.98–1.02; Appendix Figure 3).
There were differences in breastfeeding by frequency of prenatal cannabis use (Figure 1; Appendix Table 4). Compared to no prenatal cannabis use, those with monthly or less, weekly, and daily use had a higher prevalence of any breastfeeding at birth-to-1-month (aPRs=1.08–1.11, P<.05) (Table 2). Those with daily use had a lower prevalence at subsequent time points (aPR=0.77–0.96, P<.05) and those with monthly or less or weekly prenatal cannabis use had a lower prevalence of breastfeeding beginning at 4 months (aPRs=0.84–0.93, P<.05). At 12 months, any breastfeeding was highest among those with no prenatal cannabis use (41.4%), followed by monthly or less (32.0%), weekly (30.8%), and daily use (29.2%).
Similarly, prenatal cannabis use across frequency levels was associated with greater prevalence of full breastfeeding at the birth-to-1-month visit (aPR=1.12–1.17, P<.05) and a lower prevalence at 2 to 6 months (aPR=0.80–0.96,P<.05 except weekly use at 2 months, P=.12). There was a statistically significant trend (P<.001) for a decreasing likelihood of any and full breastfeeding associated with increasing frequency of prenatal cannabis use. At 6 months, full breastfeeding was highest among those without prenatal cannabis use (42.7%), followed by those with monthly or less (33.0%), weekly (29.4%), and daily use (28.4%).
DISCUSSION
As rates of cannabis use increase among individuals of reproductive age,1,2 it is critical to understand whether cannabis use is a risk factor for reduced breastfeeding initiation or early discontinuation. This retrospective cohort study leveraged data from a large, integrated healthcare delivery system with universal screening for preconception and prenatal cannabis use and routine breastfeeding assessments during standard pediatric care. Individuals with preconception and prenatal cannabis use had a higher adjusted prevalence of breastfeeding initiation but a greater risk of early breastfeeding discontinuation compared to those without cannabis use. Associations were stronger for prenatal cannabis use and higher frequency use, with similar patterns observed for full breastfeeding outcomes at 6 months. These findings complement two prior studies showing that postpartum cannabis use is associated with earlier breastfeeding discontinuation, despite similar initiation rates.7,28
While prenatal cannabis use is associated with adverse neonatal outcomes such as low birth weight, preterm birth, and admission to the neonatal intensive care unit, less is known about the health risks of cannabis use during breastfeeding.29–31 Cannabinoids are lipid-soluble and accumulate in breast milk, peaking one hour after use and persisting for up to six days.8,20,32–35 Frequent or high-dose cannabis use leads to higher cannabinoid levels in breast milk,20,36 and variation in maternal pharmacokinetics may results in differing levels of infant exposure.8 Research has focused on measuring cannabinoid levels in breast milk, and there is limited understanding of how cannabinoids are absorbed and processed by infants,33 and initial studies on the short- and long-term health effects of cannabis exposure through breastmilk are limited and conflicting.6,9,15,16 As high strength cannabis products become increasingly available,37,38 there is a critical need for lactation research that considers risks associated with both the method of cannabis use and THC concentration.
The high prevalence of breastfeeding initiation among those with preconception and prenatal cannabis use suggest strong motivation and support to start breastfeeding. However, the marked drop in breastfeeding prevalence, most pronounced around the two-month visit, may reflect a desire to resume cannabis use and concerns about the safety of cannabis use and breastfeeding. National guidelines recommend against cannabis use while breastfeeding17–19 and postpartum individuals often increase cannabis use during the first two months after delivery.8 Studies have shown that among those with postpartum cannabis use, those who believe that cannabis use while breastfeeding is not safe may discontinue breastfeeding earlier.22
Early breastfeeding discontinuation associated with cannabis use could also result from factors such as reduced alertness, diminished focus on infant hunger cues, or other cannabis-related breastfeeding challenges, such as latch difficulties, lower milk production, or altered milk composition.39 Further, results could be partially explained by unmeasured confounders, including cultural factors, mistrust of medical advice, family caretakers, or co-occurring health conditions or medications that are not accounted for in this study. Research shows that over half of breastfeeding individuals who use cannabis do so to manage mental or physical health symptoms,40,41 and those with greater health issues report more frequent cannabis use.40 Breastfeeding discontinuation among those who use cannabis may be compounded by underlying health issues and self-medication with cannabis. Further research is needed to better understand decisions related to breastfeeding and concerns for infant health among those who used cannabis before or during pregnancy.
Evidence-based equitable access to breastfeeding advice is needed as the science evolves.42 The Academy of Breastfeeding Medicine guidelines indicate that the current evidence on the health risks associated with cannabis use while breastfeeding is insufficient to recommend against breastfeeding for those who use cannabis,18 and the American College of Obstetricians and Gynecologists recommends advising against prenatal cannabis use, and continuing breastfeeding for individuals who use cannabis,17 due to the significant health benefits of breastfeeding.13 Yet, data show that nearly 40% of postpartum individuals with cannabis use in the US are advised by their health care provider not to breastfeed while using cannabis.22 Importantly, disparities exist as cannabis use was more prevalent among Non-Hispanic Black individuals in this study, consistent with prior research,43,44 and non-Hispanic Black individuals are more likely than non-Hispanic White individuals to be advised against breastfeeding if using cannabis,42 potentially exacerbating racial inequities in breastfeeding.45,46,47
Findings indicate that early screening for prenatal cannabis use could help to identify individuals with high motivation to breastfeed who may need additional support (e.g., education on breastfeeding techniques and recognition of feeding cues,48 employment or family-related resources) to successfully maintain breastfeeding. Given the benefits of breastfeeding,49 clinicians should adopt a standardized shared decision-making framework that weighs the benefits of breastfeeding against the possible risks of cannabis use,50,51 and equitably counsel patients who do not abstain from cannabis that breastfeeding remains recommended.12 Further, clinicians can discuss ways to use less frequently and minimize second and thirdhand smoke exposure (e.g., using cannabis outside, changing clothes after use). Some states with legalized cannabis have developed patient and clinician education handouts that are publicly available and can be valuable resources.52,53 Finally, many individuals with prenatal cannabis use are motivated to abstain from cannabis while breastfeeding,12 and may benefit from early mental health support and substance use interventions, as needed.
Limitations
Findings may not extend to uninsured populations, those residing outside of California, or those who leave the healthcare system during the first year postpartum. Future research is needed that includes these populations. We did not have pre-pregnancy toxicology testing, repeated measurements throughout pregnancy, mode of prenatal cannabis use or data on postpartum cannabis use. Despite adjusting for covariates, unmeasured confounding factors (e.g., medications for maternal diseases that are not compatible with breastfeeding) may have influenced the results. Gender identity has not been systematically recorded in the KPNC EHR, so we could not analyze the results by that patient characteristic, and we did not include breastfeeding intention during pregnancy as a more reliable indicator of breastfeeding plans unrelated to problems with milk production or other mechanical factors.
Conclusions
Individuals with recent cannabis use may be motivated to initiate breastfeeding but are at risk of early breastfeeding discontinuation and may need additional support to continue breastfeeding. Future research is needed to understand the mechanisms underlying the lower prevalence of breastfeeding continuation among those with prenatal cannabis use despite high initial prevalence of breastfeeding initiation.
Supplementary Material
Acknowledgments
This study was supported by grant R01DA048033 and co-funded by National Institute on Drug Abuse (NIDA) and Office of the Director, NIH (OD), R01DA047405 and K01DA043604 funded by NIDA. The funding organizations had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; or decision to submit the manuscript for publication. Sara Adams conducted the data analysis for this study. Dr. Young-Wolff had full access to all the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis. Ms. Does has received support managed through her institution from the Industry PMR Consortium, a consortium of companies working together to conduct post-marketing studies required by the Food and Drug Administration that assess risks related to opioid analgesic use. All other authors declare no financial disclosures.
Conflict of interest statement for each author:
This study was supported by grant R01DA048033 and co-funded by National Institute on Drug Abuse (NIDA) and Office of the Director, NIH (OD), R01DA047405 and K01DA043604 funded by NIDA. The study sponsor had no role in study design; collection, analysis, or interpretation of data; writing the manuscript; or the decision to submit the manuscript for publication.
Footnotes
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Credit statement:
Kelly C. Young-Wolff: Conceptualization, Methodology, Supervision, Writing – Original draft, Writing – review and editing, funding acquisition. Sara R. Adams: Conceptualization, Methodology, Formal Analysis, Investigation, Data curation, Writing – original draft, Writing – review and editing. Kenya Homsley: Methodology, Writing – review and editing. Stacey E. Alexeeff: Conceptualization, Methodology, Supervision, Formal Analysis, Writing – review and editing. Erica P. Gunderson: Methodology, Writing – review and editing. Monique Does: Project administration, Writing – review and editing. Deborah Ansley: Writing – review and editing. Carley Castellanos: Writing – review and editing. Erica Haley: Writing – review and editing. Lyndsay A Avalos: Conceptualization, Methodology, Supervision, Writing – review and editing, funding acquisition.
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