Marijuana has been said to both increase and decrease anxiety or nervousness. A recent review article (Crippa et al Human Psychopharmacology 24: p 515-523, 2009) clarifies this seeming contradiction. When scientists find an association between two events (e.g. A and B), then it could mean A causes B, B causes A, or something else else causes both A and B to occur at the same time. The evidence that marijuana causes increased anxiety is limited to two scenarios: new users of marijuana (i.e. “bad highs”) and high-strength marijuana in regular users. Often this causes “panic attacks” which include increased heart rate, paranoia, or feeling like one is “losing their mind”, etc. Most of the evidence indicates marijuana use does not cause a clinically significant anxiety problem. In fact, marijuana use among regular users appears to decrease anxiety in those who are currently anxious; e.g. among those giving a speech. Although THC is the major chemical that causes the subjective effects of marijuana, other similar compounds (called “cannabinoids”) can decrease anxiety as well. Also, stopping marijuana can cause a withdrawal syndrome that causes anxiety. Anxious persons do appear to be more likely to take up marijuana use and do report it decreases anxiety, although they do not necessarily become less anxious people. This type of use of marijuana has been called “self-medication.” Finally, genes, temperament and personality have been thought to both increase anxiety and increase use of marijuana at the same time but the evidence for this is small.
–Dr. John R. Hughes