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. 2013 Jan 23;4:11–27. doi: 10.2147/SAR.S25869

Table 3.

Effects of cannabis use on memory performance

Author Subjects Age in years (M) Age of onset of use (M) Cannabis use in years (M) Joints [episodes]/lifetime (M) Joints/month (M) Days of use/month (M) Abstinence period Controlled confoundera Memory testsb
Former cannabis users (history of cannabis use, ≤ 12 joints in the last 3 months)
Pope73 n = 45 41 NR 15 (median) 11,000 (median) ≤2 last 3 months NR 7 days DU, PC, PsyM, A, G, IQ BVRT″
BSRT″
Fried et al74 n = 16 18 14 2.2 2203 0 NR Day of testing (NS) DU, PC, PsyM, A, G, SES WAIS-PS″
WMS″
Current regular cannabis users (<30 joints/month or <20 days/month or <2000 joints/lifetime)
Jager et al77 (fMRI) n = 10 23 NR 7.1 1300 (median) NR NR 1 week DU, PC, MC, PsyM, A, G, IQ SMT″
Jager et al78 (fMRI) n = 20 25 NR NR 1900 (median) NR NR NU DU, PC, MC, PsyM, A, G, IQ PMT″
Grant et al111 n = 16 22 NR NR NR NR 12 NR DU, PC, A, G, SES, E CANTAB-OTSC* CANTAB-RVIPT″
CANTAB-SWM″
Harvey et al113 n = 34 16 NR NR NR 12 (median) 12 (median) 12 hours DU, PC, A, G CANTAB-RVIPT*
CANTAB-SWM*
RAVLT* 		CANTAB-SS″
WAIS-WM″
CANTAB-PAL″
Current heavy cannabis users (≥30 joints/month or ≥20 days/month or ≥2000 joints/lifetime)
Kanayama et al96 (fMRI) n = 12 38 NR NR 19,200 ≥28 NR NR DU, PC, MC, PsyM, G, E SDRT″
Smith et al112 (fMRI) n = 10 20 NR 4.6 2697 46 NR <5 hours DU, PC, IQ, PF N-BACK″
Messinis et al83 n = 20 24 NR 7 NR ≥16 21 123 hours (M) DU, PC, MC, PsyM, G, IQ, E RAVLT*
VFT* 		BNT″
Solowij et al33 n = 51 29 NR 10.2 NR NR 27 17 hours (M) DU, PC, A, G, IQ RAVLT″
WCST″
AT″
ON″
PASAT″
Fontes et al82 n = 55 30 19 10.9 6790 51 NR 4.1 days (M) PC, MC, A, IQ, E WCST* WAIS-VC″
Bolla et al30 n = 7 21 NR 5.3 NR 375 NR 28 days DU, PC, A, G, IQ CFT*
PAL*
WCST*
RAVLT* 		WMS″
Short-term cannabis users (<4 years of cannabis use)
Schweinsburg et al79 (fMRI) n = 15 17 NR 3.4 310 NR 13 48 hours DU, PC, MC, PsyM, A SWMT″
Schweinsburg et al80 (fMRI) n = 13 17 NR 2.3 342 NR 14 3.3 days (M) DU, PC, MC, PsyM, A, G, IQ, SES SWMT″
Schweinsburg et al80 (fMRI) n = 13 18 NR 2.7 515 NR 17 38 days (M) DU, PC, MC, PsyM, A, G, IQ, SES SWMTv
Medina92 n = 31 18 NR 2.91 541 57 NR 28 days PC, MC, A, G, SES, E WMS* CFT″
CVLT″
Fried et al74 n = 19 18 16 1.8 122 6 NR Day of testing (NS) DU, PC, PsyM, A, G, SES WMS″
Block et al109 (PET) n = 18 NR NR 3.9 NR 72 NR 16 hours (M) DU, PC, PsyM, A, G, BV, HW BSRT* WAIS-PS″
Long-term cannabis users (cannabis use > 15 years)
Pope73 n = 63 36 NR 19 (median) 18,720 (median) ≥28 NR 7 days DU, PC, PsyM, A, G, IQ BSRT* BVRT″
Messinis et al83 n = 20 33 NR 15.6 NR ≥16 20 ≥24 hours DU, PC, MC, PsyM, G, IQ, E BNT*
RAVLT*
VFT*
Battisti et al84 n = 24 36 17 (median) 17.0 NR 435 (median) 30 (median) 12 hours PC, MC, A, G, E VMT*
Solowij et al33 n = 51 41 NR 23.9 NR NR 28 17 hours (M) DU, PC, A, G, IQ AT*
RAVLT* 		ON″
PASAT″
WCST
Late-onset cannabis users (≥17 age of onset)
Fontes et al82 n = 49 30 21 8.7 5160 45 NR 3.8 days (M) PC, MC, A, IQ, E WCST″
WAIS-VC″
Pope et al85 n = 63 44 ≥17 NR 12,480 (median) NR NR 28 days DU, PC, PsyM, A, G WCST* BSRT″
BVRT″
WMS″
Early-onset cannabis users (<17 age of onset)
Solowij et al31 n = 52 19 16 2.4 NR 17.5 14 (median) 20 hours (median) DU, PC, G, IQ, E RAVLT*
Fried et al74 n = 19 18 15 2.6 1884 12.4 NR Day of testing (NS) DU, PC, PsyM, A, G, SES WAIS-PS*
WMS*
Hanson et al75 n = 19 18 16 NR 465 NR 16 3 days PC, MC, A, G, IQ, SES HVLT*
WAIS-WM*
Ashtari et al97 (MRI) n = 14 19 13 5.3 NR 174 NR 6.7 months (M) DU, PC, A, G, IQ, SES, BV CVLT″
Nestor et al138 n = 35 22 16.5 5.7 NR NR 23 15 hours (M) DU, PC, MC, PsyM, A, G, IQ FNPL*
Gruber et al32 n = 34 23 15.5 7.24 ≥2500 77 NR 12 hours DU, PC, MC, PsyM, A, IQ WCST* CFT″
CVLT″
COWAT″
Pope et al85 n = 69 36 <17 NR 17,368 (median) NR NR 28 days DU, PC, PsyM, A, G BSRT*
WCST* 		BVRT″
WMS″
Jager et al102 (fMRI) n = 21 17 13 NR 4006 NR NR 5.1 weeks (M) DU, PC, MC, PsyM, IQ PMT″
SMT″

Notes:

*

Poorer performance when compared to noncannabis users;

″

no differences in performance when compared to noncannabis users;

a

controlled though exclusion, matching, or statistical methods;

b

see Table 1.

Abbreviations: M, mean; n, number; NR, not reported; DU, other drug use; PC, psychiatric condition; PsyM, psychoactive medication; A, age; G, gender; IQ, Intelligence Quotient; BVRT, Benton Visual Retention Test; BSRT, Buschke Selective Reminding Test; NS, not further specified; SES, socioeconomic status; WAIS-PS, Wechsler Adult Intelligence Scale (Processing Speed Index); WMS, Wechsler Memory Scale; MC, medical condition; SMT, Sternberg Memory Task; NU, negative urine toxicology; PMT, pictorial memory task; E, education; CANTAB-OTSC, Cambridge Neuropsychological Test Automated Battery One-Touch Stockings of Cambridge; CANTAB-RVIPT, Cambridge Neuropsychological Test Automated Battery rapid visual information processing task; CANTAB-SWM, Cambridge Neuropsychological Test Automated Battery Spatial Working Memory; RAVLT, Rey Auditory Verbal Learning Test; CANTAB-SS, Cambridge Neuropsychological Test Automated Battery spatial span; WAIS-WM, Wechsler Adult Intelligence Scale (Working Memory Index); CANTAB-PAL, Cambridge Neuropsychological Test Automated Battery Paired Associate Learning Test; SDRT, short-delay response task; PF, personality factors; N-BACK, N-back task; VFT, verbal fluency task; BNT, Boston naming test; WCST, Wisconsin Card Sorting Test; AT, alphabet task; ON, omitted numbers; PASAT, Paced Auditory Serial Addition Test; WAIS-VC, Wechsler Adult Intelligence Scale (Verbal Comprehension Index); CFT, Rey–Osterrieth Complex Figure Test; PAL, paired associate learning test; SWMT, spatial working memory task; CVLT, California Verbal Learning Test; PET, positron emission tomography study; BV, brain volume; HW, height and weight; VMT, verbal memory task; HVLT, Hopkins Verbal Learning Test; MRI, magnetic resonance imaging study; FNPL, face–name pair learning; COWAT, controlled oral word association test; fMRI, functional magnetic resonance imaging study.