Kratom Use Is Underestimated, but Prevalence Still Appears to Be Low

Henningfield et al.¹ commented on my manuscript estimating that 0.7% of individuals in the U.S. have used kratom in the past year.² They add to my noted limitations about under-representation of high-risk groups that kratom use is underestimated. I agree that kratom use is underestimated, but not greatly.

As the authors point out, new psychoactive substance use is under-reported. This is often because people are unknowingly exposed to such drugs as adulterants.³ My colleagues and I have argued that new psychoactive substance use is severely under-reported on the National Survey on Drug Use and Health (NSDUH), the data set used to estimate kratom prevalence, but this is because NSDUH does not directly query new psychoactive substance use.⁴ NSDUH relies on participants to type in names of drugs they used that they were not asked about, and this is what leads to severe underestimation of use. For example, in 2018, the year before NSDUH began asking about kratom use, ≤5 participants typed in kratom as a response (of 56,313 participants).⁵

Henningfield et al.¹ are also correct that NSDUH underestimates heroin use.⁶ However, even if it is assumed that prevalence of past-year heroin use was double the current estimate of 0.3% (0.6%) and that all of these individuals use kratom, the current estimate of past-year kratom use would still not likely surpass 1%.

Henningfield et al.¹ present industry report estimates based on sales volume, but it is difficult to estimate the number of people who use based on volume of product sold. An industry report cited by the authors divided monthly sales volume by an estimate that consumers use on average 125 grams per month (4.2 grams per day). Based on the 2020 U.S. Census, this equates to a prevalence estimate of 5% of the U.S. population using in the past month, which is 16.7 times higher than the NSDUH estimate of 0.03% of people using in the past month. This industry report estimate is based on an oversimpli-fication. A study of people who use kratom does suggest that the plurality of people who use this substance use 1−3 grams as their typical dose, but 9% report using ≥7 grams as a typical dose, and the average number of doses taken per day is 2.7 (SD=1.3).⁷ Dividing volume by a suspected average dose will not likely produce accurate estimates because, as has been shown with drugs such as alcohol and cannabis, volume tends to reflect a large amount used by frequent users and a small amount used by occasional users.⁸ Furthermore, sales do not equate to use but perhaps more to availability.

If past-month prevalence is indeed as high as 5%, then this would make kratom use more prevalent than past-month use of all illegal drugs other than cannabis⁹ and more prevalent than past-month use of dietary supplements such as vitamin A, selenium, iron, coenzyme Q10, probiotics, ginkgo biloba, amino acids, and fiber.¹⁰ This may be possible, but as Henningfield et al.¹ suggest, we need better data. Kratom use may be underestimated, but it is not likely that use is as prevalent as they suggest.