Of course drugs have medicinal uses, and some of the most addictive are given for pain relief. None of these states satisfies any pre-existing physical desire. Sex, by way of contrast, is an instinctual desire, since the urge comes before the experience begins. People don't get hooked on sex because they tried it once, and virgins have the same appetite for it that everyone else has. Mind alteration is neither instinctual nor universal.
People try drugs because they want to be released from the world they are living in.
They open an escape route out of awareness of one's surroundings or out of oneself. Those trapped in such psychic pain have an obvious and understandable motive to seek this release. Yet even those who are comfortable with themselves, those on friendly terms with the world they live in, may sometimes feel suddenly and disturbingly estranged from it. The appeal of a mind-altering drug may be its ability to repeat or intensify that estrangement, that alienating yet alluring sense of being somebody else or somewhere else. Spirituality can produce the same effect.