My primary research field is cancer drugs, but my teaching brings me into the realm of drugs of abuse, simply because so many of those drugs are naturally-occurring. So, my views must be taken in that perspective. In the US, I think that it is morally difficult to justify the legality of addictive drugs like alcohol and tobacco while restricting other psychoactive compounds. I do not advocate for other drugs to be used recreationally. I just feel that US laws need to be consistent. Our experiment with criminalizing alcohol was an abysmal failure that fostered organized crime. Our continued experiment with criminalizing other drugs has been equally a failure. However, I am very much against a libertarian argument that society should be free to determine what they want because, frankly, many drugs impair one's decision-making ability.
But I like your question: many drugs declared illegal for recreational use are among the most useful therapeutics for pain, especially the pain associated with surgery and cancer. My greater humanistic concern is that our society's zero tolerance approach to drugs that "could" be illegal is that people who need them for their desired effect often go without. Undermanagement of pain is the major casualty of the war on drugs. No, let me fix that. People who suffer unnecessarily from pain when useful drugs could be used are the major casualties of the war on drugs.