There is more that science doesn’t know about cannabis than what it does know. This includes CBD and THC, compounds in cannabis that may offer medical benefits.
There have been few high-quality scientific studies on cannabis. Most of what is offered as evidence for the medical benefits of cannabis is really a collection of subjective patient reports. These reports haven’t received scientific scrutiny — the kind of scrutiny that is standard in bringing prescription drugs to the U.S. Food and Drug Administration for approval. Lack of data makes it hard to recommend cannabis as either safe or effective.