Even though the United States government still classifies cannabis as a Schedule I drug with no medical use, a wealth of research has confirmed that this once-demonized plant does indeed have a powerful therapeutic potential. Now that the majority of the country has legalized at least some form of medical marijuana, researchers are beginning to investigate whether other federally-prohibited drugs may also have therapeutic value.

In a new meta-analysis recently published online in the Journal of Affective Disorders, British researchers studied earlier research exploring the effectiveness of psychedelic drugs as a treatment for depression or anxiety. The current study examined seven prior clinical studies including a total of 130 patients who were suffering from one or both of these conditions.

So far, most of the research into natural psychedelics has focused on psilocybin, the psychoactive ingredient in magic mushrooms. In one pair of studies, patients suffering from depression and anxiety reported a significant improvement in their symptoms six months after ingesting psilocybin in a controlled setting. Three other double-blind trials also found that psilocybin could help reduce symptoms of anxiety, depression, or both.

In another small study, doctors administered two different doses of LSD to 12 patients who were suffering from anxiety associated with terminal illnesses. Two months later, the patients who received the larger dose of LSD reported a significant reduction in their anxiety, compared to those who received the smaller dose. In an even smaller study, six patients who took a single dose of ayahuasca scored 82 percent lower on a test measuring depressive symptoms after three weeks.

Gallery — Smoke Weed, Eat Shrooms, and Shine:

“In all studies, psychedelic administration caused statistically significant reductions in depression and anxiety symptoms,” the researchers wrote, according to Marijuana Moment . “These findings corroborate the limited previous research conducted in animal studies and healthy volunteers, as well as anecdotal evidence describing improved mood and reduced feelings of apprehension following psychedelic administration.”

In their meta-analysis, the researchers discovered that “psychedelics were well-tolerated” by patients. “The most common adverse effects were transient anxiety, short-lived headaches, nausea, and mild increases in heart rate and blood pressure.”

“Given the limited success rates of current treatments for anxiety and mood disorders, and considering the high morbidity associated with these conditions, there is potential for psychedelics to provide symptom relief in patients inadequately managed by conventional methods,” the study concludes . “The novelty of this research means that before psychedelics’ wider-use can be contemplated, the results presented herein need to be replicated in larger studies with a longer followup to determine lasting efficacy and safety.”

Although research into the therapeutic potential of psychedelics is still in its infancy, preliminary studies are still presenting promising findings. A 2016 NYU study found that a single dose of psilocybin can help treat the symptoms of cancer-related psychological distress, and a more recent study found that LSD and psilocybin can help alcoholics stop drinking .

Based on the strength of this evidence, advocacy groups around the world have been working to overturn the prohibition of these potential medicines. In May, Denver decriminalized psilocybin, and in June, Oakland decriminalized pretty much every natural plant-based psychedelic. In Vancouver , a cannabis activist is selling microdosed mushroom capsules online, even though psilocybin is still illegal in Canada.