Normally Big Pharma foots the bill for such trials, but thus far the pharmaceutical companies have shown scant interest in psychedelics. For one thing, this class of drugs offers them little if any intellectual property: psilocybin is a product of nature, and the patent on LSD expired decades ago. For another, Big Pharma mostly invests in drugs for chronic conditions, the pills you have to take every day. Why would it invest in a pill patients might only need to take once in a lifetime?
