A historical U.S. survey analysis reported that past-year methamphetamine use approximately doubled among respondents who also reported past-year LSD use. That finding describes a changing population percentage. It does not show that LSD caused methamphetamine use, that individuals progressed from one drug to the other, or that the substances were taken together on a particular occasion.
Which population and years were studied?
Palamar, Han and Keyes analyzed 226,632 respondents aged twelve and older in the 2015–2018 National Survey on Drug Use and Health. These were annual cross-sectional surveys of the noninstitutionalized population, not repeated follow-up interviews with one cohort.
The analysis used survey weights and accounted for the complex sampling design. The sample count is therefore different from the population represented by the weighted percentages. The findings concern 2015–2018 and are not estimates of present-day prevalence.
Earlier years were not pooled because the survey was redesigned in 2015, including changes to questions about methamphetamine and other drugs. A visually continuous trend across that redesign would require additional justification.
What exactly doubled?
Among respondents reporting LSD use in the preceding year, estimated past-year methamphetamine use increased from 5.1% in 2015 to 10.3% in 2018. The reported 95% confidence intervals were 3.4%–7.7% and 7.3%–14.3%, respectively. The linear trend had p=0.002.
The paper reported a 100.4% relative increase and a 5.2-percentage-point absolute increase. A relative increase near 100% means the starting percentage approximately doubled; it does not mean that nearly everyone in the subgroup reported methamphetamine use. Published percentages are rounded, so recalculating relative changes from the displayed endpoints need not reproduce the authors’ result exactly.
The denominator was people reporting past-year LSD use. The result is not the percentage of people reporting methamphetamine use who also reported LSD, and neither percentage is the prevalence of methamphetamine use in the entire population.
How did the whole-population trend differ?
The authors reported overall past-year methamphetamine prevalence rising from approximately 0.62% to 0.70%, with p=0.039 and a reported relative increase of 13.2%. The much larger change in the LSD-reporting subgroup therefore answers a narrower question than the modest overall change.
Other drug-defined subgroups also showed increases, including those reporting heroin, cocaine, ecstasy/MDMA or prescription opioid misuse. These categories overlap. A respondent can belong to several, so their estimated changes cannot be added as if they describe mutually exclusive populations.
Was the LSD finding just a reflection of heroin reporting?
The researchers repeated the analysis among respondents who did not report past-year heroin use. Within that restricted population, methamphetamine use among people reporting LSD increased from 4.3% to 8.1%, with a reported relative increase of 86.6% and p=0.019.
This sensitivity analysis makes the descriptive finding more specific: it persisted after excluding respondents reporting heroin. It does not remove every possible shared influence or establish a causal effect of LSD. Other drug use, social circumstances and differences in the composition of each annual subgroup can remain relevant.
The paper also found smaller quadratic trends for some prescription-drug categories in that restricted analysis. A quadratic trend is not interchangeable with a steady linear increase. Preserving the model description matters when a claim concerns how prevalence changed over time.
Can the survey show that the drugs were used together?
Both reports concerned the preceding year. The survey analysis did not establish the interval between methamphetamine and LSD use, the sequence of initiation, simultaneous ingestion, dose, purity or route on a particular occasion. It included no paired blood concentrations identifying a pharmacological interaction.
A change in an annual subgroup can also occur without the same individuals changing their behavior. Each year’s respondents and the population represented by that subgroup may differ. Describing this result as proof that LSD users individually moved on to methamphetamine would turn a repeated cross-sectional comparison into a longitudinal claim.
Which uncertainties belong in a client explanation?
The authors identify possible underrepresentation and underreporting of methamphetamine and heroin use, declining survey response and limited geographic detail. Unrecognized exposure would also escape a question asking respondents whether they used a drug. Self-report is not a chemical confirmation of every exposure.
The paper examined numerous demographic and drug-use trends; its methods describe trend models rather than a blanket correction for all comparisons. The reported p-values should be presented with that exploratory setting, the confidence intervals and the study’s sampling limits.
The supported conclusion is that this historical survey detected a substantial relative change within a particular reporting subgroup. It can motivate further research into contexts and prevention needs. It cannot determine the exposure history, diagnosis, impairment or causal pathway of an individual client.
Scientific source
Palamar JJ, Han BH, Keyes KM. Trends in characteristics of individuals who use methamphetamine in the United States, 2015–2018. Drug and Alcohol Dependence. 2020;213:108089. doi:10.1016/j.drugalcdep.2020.108089. Historical repeated cross-sectional human survey analysis; full author manuscript read from the supplied research collection.
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