Yes, but some drugs have medicinal value and others don't. Some drugs can be helpful for medicinal reasons if not abused and others don't. BTW, you won't get far with the "cigarettes and alcohol are legal" stuff with me (I know these pothead arguments like the back of my hand). You can't argue that all poisons should be legal because some already are. That's specious. Our country has been harmed enough by tobacco and alcohol - we don't need more poisons competing on the marketplace.
Arguing for utilitarianism as a guiding principle of governance is specious.