There is little question from clinical experience that psychedelics can be behaviorally toxic, even if they are not addicting in the way cocaine or alcohol are. Bad trips and flashbacks occur with some frequency in recreational users — and sometimes hallucinogens can unleash a psychotic disorder in those who are genetically at risk. Microdoses are supposedly too small to cause those effects, but again, it could be easy to take more by accident.

The bottom line is that we don’t know how safe or effective psychedelics are because most of the data have been anecdotal or from small trials. Part of the reason is that hallucinogens have been classified as Schedule I drugs, the most restrictive category, reserved for drugs considered to have no legitimate medical use and to have a high abuse potential. This makes it somewhat difficult for researchers to conduct large studies, but it is by no means an absolute bar; there are many trials of Schedule I drugs like THC and cannabinol, active molecules in marijuana.

I am anxious that we do not repeat the mistake that we made with cocaine. Aside from Freud’s glowing 1884 monograph on cocaine, “Über Coca,” in which he described his research on cocaine — and his addiction to it — there was little modern research on the drug. In the ’70s and ’80s, people assumed that the absence of data that cocaine was addictive meant that it was safe and dismissed concerns as hysterical moralizing. An epidemic followed.

Psychedelic drugs don’t come close to the toxicity or abuse potential of cocaine. But we can’t assume they are perfectly safe just because we don’t yet have serious evidence of harm.

Psychedelics might turn out to have real promise, but that needs to be proven through large, rigorous, placebo-controlled trials. We’re not there yet.

In the end, I suspect they may prove more interesting as probes of brain function — perhaps illuminating the neural basis of extraordinary mental states, like our experiences of mysticism — than as therapeutic agents. What they tell us about our brain is probably more valuable than what they can do for us.