There has been a recent resurgence of interest in psychedelic drugs' potential to address conditions like anxiety and depression.

That research is beginning to lead to the development of new and novel prescription drugs.

Illicit drugs like mushrooms, ecstasy, and ketamine are inspiring a range of potential treatments for diseases that currently lack good medications.

Like a May shower, the studies on psychedelic drugs' potential therapeutic benefits came — first as a sprinkle, then a steady downpour. Between 2012 and 2017, the papers abounded. One, published in 2016, suggested that magic mushrooms might alleviate anxiety in cancer patients; another in 2017 indicated that ecstasy could help veterans cope with PTSD symptoms; and one in 2012 hinted that ketamine might curb major depression.

Recently, the shower has turned into a trickle. But that spate of published research on psychedelics now seems to be leading to the development some promising potential treatments.

Drugs based on the effects of shrooms and ketamine are being tested for their potential to treat mental illnesses like depression and anxiety. Some are being studied in the types of clinical trials that could eventually make them candidates for federal approval, while others could get a green light as soon as this summer.

Ketamine is inspiring a handful of novel drugs for depression

A widely used anesthetic that is also known as a party drug, ketamine was shown to have benefits as a rapid-fire antidepressant nearly a decade ago. Early studies suggested ketamine could help people who failed to respond to existing medications or were suicidal.

The authors of one paper called ketamine "the most important discovery in half a century."

As opposed to existing antidepressants, ketamine acts on a brain mechanism that scientists have only recently begun to explore. Homing in on this channel appears to provide relief from depression that is better, arrives faster, and works in far more people than current drugs.

After a lack of new drugs for depression spurred scientists to go back to the drawing board, pharmaceutical companies like Allergan and Johnson & Johnson are now in hot pursuit of new blockbuster depression drugs that take after ketamine. Allergan's drug is in the last phase of clinical trials and has received a key FDA designation designed to speed it through the approval process. Johnson & Johnson presented promising research on its drug on Saturday and told Business Insider that it expects to file for FDA approval this year.

A compound in marijuana is showing promise in some forms of epilepsy

Marijuana has been anecdotally linked with numerous health benefits. But the comprehensive science backing up those claims has been scarce, in large part because of federal laws restricting research on the drug. Despite this, some pharmaceutical companies and startups have charged ahead.

GW Pharmaceuticals is a British drugmaker that's working on a medicine derived from the marijuana compound CBD. That drug, called Epidiolex, is designed to treat two rare forms of childhood epilepsy.

Epidiolex recently won a major green light from the FDA that could set it on the path to be the first federally approved cannabis-based drug. A final FDA decision on the drug is expected this June.

A type of ecstasy might accelerate PTSD therapy

Rick Doblin, founder of the Multidisciplinary Association for Psychedelic Studies — a leading nonprofit behind psychedelic research — believes ecstasy is the "most likely" psychedelic to get adopted first by mental health professionals.

Ecstasy, otherwise known as MDMA, was created by pharmaceutical company Merck in 1912. As both a stimulant and a psychedelic, the now illegal drug has energy-raising and hallucinogenic properties. In the brain, MDMA amps up the activity of chemical messengers involved in mood regulation. It's also been known to be dangerous when used without medical supervision because it raises body temperature and blood pressure.

Yet researchers who study it say a formulation of the drug could make for an ideal treatment for some types of mental illness. One arm of Doblin's research involves studying MDMA in people with PTSD in a setting that combines the drug with traditional talk therapy. In three of the sessions, patients are given the drug or a placebo and talk therapy; in another 12 sessions, they are given talk therapy alone.

Results of one of those studies, published this month in the journal The Lancet Psychiatry, suggest that adding MDMA to standard therapy works fairly well — after the year-long study, roughly two-thirds of the 26 participants no longer qualified for a PTSD diagnosis. Those who retained their diagnosis said they experienced a reduction in their symptoms. But the treatment was tied to some unpleasant side effects including insomnia, tiredness, and headaches.

The results and the fact that MDMA received an FDA "breakthrough therapy" designation — a label designed to hasten the research and approval process — convinced some experts that the drug will be approved as early as 2021. The next phase of research is set to begin this summer and will involve roughly 250 people.

A compound in magic mushrooms is showing promise for anxiety

Last year, researchers studying psilocybin, the main psychoactive ingredient in hallucinogenic mushrooms, likened its quick effects on cancer patients with anxiety and depression to a "surgical intervention" for the mental illness.

Brain scan studies suggest that depression ramps up the activity in brain circuits linked with negative emotions, and weakens the activity in circuits linked with positive ones. Psilocybin appears to restore balance to that system.

With that in mind, a company called Compass Pathways, which is backed by entrepreneur Peter Thiel, has plans to start its own clinical trials of magic mushrooms for depression later this year.

Some researchers have high hopes that a psilocybin-inspired drug will get approved within a decade. David Nutt, director of the neuropsychopharmacology unit at Imperial College London, told Business Insider last year that he believed psilocybin would become an "accepted treatment" for depression before 2027.