Bhaava darling you can support a person's right to do what they want with their own body without actually having to do the thing yourself.
The problem here is national health care.IF you make health care a government controlled "right" and if marijuana results in more cases of people needing treatment paid for by those who do not take drugs, the user is enjoying himself and passing the responsibility on to others.
The obvious answer then is yes man should be able to harm himself anyway he chooses. No he does not have the right to burden others. Ergo legalize drugs and return health care completely into private hands.