Cannabis intoxication alters metabolism, but frequent users show fewer effects

A new study published in Neuropsychopharmacology has found that cannabis intoxication leads to distinct metabolic changes in the blood, and these changes differ between occasional and chronic users. Researchers identified 14 metabolites that could distinguish between these two groups even when they were not intoxicated. They also discovered that cannabis affected attention and subjective intoxication differently in each group, with occasional users experiencing greater cognitive impairment. These findings suggest that metabolic markers could help differentiate cannabis use from cannabis-induced impairment, a distinction that current drug tests fail to make.

Cannabis is one of the most widely used psychoactive substances in the world, with millions of people consuming it for recreational or medical purposes. One of the primary concerns about cannabis use is its potential to impair cognitive functions such as attention and reaction time, which are important for activities like driving. However, not everyone experiences the same degree of impairment. Occasional users tend to be more affected by cannabis than chronic users, who often develop tolerance.

The legal system relies on drug tests that detect cannabis in bodily fluids such as blood or saliva, but these tests only indicate past use—they do not measure whether someone is currently impaired. This is a major issue in legal cases, such as those involving driving under the influence. Researchers wanted to see if measuring metabolic changes in the blood could provide a better way to assess whether someone is impaired by cannabis rather than just confirming they have used it.

To investigate this, researchers recruited 35 healthy cannabis users, who were divided into two groups based on their use patterns. The 18 occasional users consumed cannabis up to three times per week, while the 17 chronic users consumed it at least four times per week. Participants took part in a double-blind, placebo-controlled experiment where they inhaled vaporized cannabis containing THC (the primary psychoactive compound in cannabis) on one test day and a placebo on another test day. The amount of THC was carefully controlled to ensure consistency.

Blood samples were collected before and at multiple time points (10, 30, 50, and 70 minutes) after cannabis or placebo use. Researchers analyzed these samples to identify metabolic changes. Participants also completed an attention task and rated how intoxicated they felt at different time points.

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The study revealed key differences in the metabolic profiles of chronic and occasional cannabis users. Even before consuming cannabis, the two groups had distinct metabolomic fingerprints. Chronic users had lower levels of certain metabolites related to endocannabinoid and amino acid metabolism, including 2-arachidonoyl glycerol (2-AG) and tyrosine. These changes could be linked to long-term neuroadaptations in response to frequent cannabis use.

After cannabis consumption, occasional users showed significant increases in organic acids and ketone bodies such as β-hydroxybutyrate, which are involved in energy metabolism. These metabolic changes were linked to increased attention lapses and feelings of intoxication. In contrast, chronic users showed only minor metabolic shifts, primarily involving amino acids such as leucine, isoleucine, and tyrosine. This suggests that frequent cannabis use alters the body’s metabolic response to THC, potentially explaining why chronic users experience fewer cognitive impairments.

Researchers also found that certain metabolites, particularly lipids such as hexosylceramides, were associated with the degree of cognitive impairment and subjective intoxication in occasional users. Elevated levels of these compounds correlated with worse attention performance and higher ratings of being high. In contrast, chronic users exhibited fewer metabolic changes linked to cognitive impairment, reinforcing the idea that their bodies have adapted to frequent cannabis use.

While this study provides strong evidence that metabolic markers can distinguish between cannabis use and cannabis-induced impairment, it is not yet ready for practical application. The study involved a relatively small sample size, and more research is needed to confirm these findings in larger and more diverse populations. Additionally, researchers need to determine whether these metabolic changes are unique to cannabis intoxication or if they also occur with other substances.

Future studies could explore whether a single blood sample taken at the time of testing—without a prior baseline measurement—can still reliably indicate impairment. Researchers may also investigate whether a continuous measure of cannabis use, rather than a simple division into occasional and chronic users, provides a more precise understanding of how metabolic responses vary.

The study, “Metabolomic profiling of cannabis use and cannabis intoxication in humans,” was authored by Francisco Madrid-Gambin, Noemí Haro, Natasha L. Mason, Pablo Mallaroni, Eef L. Theunissen, Stefan W. Toennes, Oscar J. Pozo, and Johannes G. Ramaekers.