One thing primitive tribes around the world have in common is the pursuit of ecstasy, the complete escape from the external world into a dreamscape universe. For some reason most advanced agricultural societies turned against the hallucinogenic drugs and savage rituals that generate these states; since the Bronze Age humans have mostly limited themselves to mild stimulants and the numbing effects of alcohol.
Recently scientists and doctors, frustrated by their inability to cure the widespread anxiety and depression that are among the worst banes of modern life, have taken renewed interest in mind-altering drugs. Study after study has shown that in certain circumstances they make certain people feel much, much better. I have written here about using ketamine to treat depression, and just yesterday MDMA to use post-traumatic stress disorder. Today there is news of a new study that found success using psilocybin to treat depression in cancer patients.
I feel certain that there is something to these studies. After all the desire for mind-altering drugs is so widespread among humankind (and also other species) that it must be a response to a biological need. Evolution, it seems, does not care how you feel, and in fact it sometimes achieves its ends by making you feel really awful. And sometimes there is nothing we can do to resolve those stresses through action. Hence, drugs.
But I would make two big caveats about all this good news. One is that while these drugs may help some people, they don't help everyone, and sometimes they hurt a lot. The "bad trip" is a big part of LSD lore because it really happens. Sometimes the bad effects persist for a long time. Richard Feynman, a bad-boy physicist who reveled in defying the man, recounted in his memoirs that although he was always fascinated by ecstatic experiences he decided in the end not to try LSD. He had read and heard too many believable accounts of people who suffered long-term mental damage to take the risk. Of course if you are so crippled by depression or anxiety that you can't function, or if you are slowly dying of cancer, your calculus might be different.
The other caveat is that making these drugs available medically will inevitably make them more available on the street, and it will also inevitably invite more people to self-medicate with them rather than seeking professional help. Any drug that helps you feel better can lead to dependence. We are living with the profound bad effects of making pain medication more available for people who are really suffering, and making psilocybin a common crutch for the troubled would probably be another disaster.
There are few unalloyed goods in the world; everything else comes with a downside. Given how many people suffer now from mysterious mental woes, and how many of them have already screwed themselves up with alcohol or opiates, I think making hallucinogens and hypnotics more available is worth the risk.