Two studies, one from NYU, and one from Johns Hopkins have shown that a single dose of psilocybin (sil-o-sigh-bin) was enough to reduce the symptoms of depression and anxiety associated with a cancer diagnosis.
The drug comes from a mushroom, and has been used for many years for its hallucinogenic properties. In the trial, the intensity of the hallucinogenic effects was linked to better depression/anxiety responses. The responses last for (at least) months in many of the patients.
NOTE: Just to be clear - This post is NOT suggesting that cancer patients (or anyone else) take unapproved/non-prescribed drugs of any kind.