A review of four clinical trials found that psilocybin-assisted therapy produced immediate and substantial improvements in depression that could last up to six months. Two of the trials involved 32 patients with treatment-resistant depression; the other two involved 80 patients with cancer-related anxiety and depression. The authors note that the small sample sizes mean future studies are needed to confirm the positive association and to fully understand psilocybin's mechanisms and effects.
Ibogaine, a natural alkaloid from the African shrub Tabernanthe iboga, has been used to treat substance abuse but is illegal in several countries due to hallucinogenic and cardiotoxic effects. It acts on multiple sites in the central nervous system and heart, which may explain its efficacy in reducing drug-seeking behavior and opioid withdrawal symptoms. However, over 30 deaths since 1990 are linked to ibogaine, likely from cardiac effects. Contributing factors include the long half-life of its active metabolite noribogaine, accumulation in adipose tissue, and poor metabolizer status. Further study of ibogaine's medical uses and adverse effects is needed.