Some drugs have more pronounced physical and others more pronounced mental effects, though all have some of both. For example (and I cannot speak knowledgeably of all drugs) LSD, psilocybin and THC do not impair motor skills much. Use of each is difficult to detect by having someone walk a straight line or touch their nose (assuming they do not think their nose a giraffe or the line made of stardust. ) Slurred speech is rarely pronounced either, though rambling speech quickly and often jumping between many diverse topics often is. As Neal Cassady once told his wife, "the thing about being stoned is, if you HAVE to do something, you can," though concentration can be a challenge.

Put another way: You have often been in chat with the same person when he was very stoned, and on other occasions when he was very drunk. Do you recall which state routinely caused his typing skills to deteriorate until the text was barely readable, and which left typing skill (if not choice of topics) practically unaffected?

Flip side, I have never heard of alcohol causing hallucinations except as a withdrawal symptom of advanced delireum tremens. A commonly reported problem in confronting PCP users is that, as a powerful anesthetic, it makes them almost insensible to injury and pain that would normally incapacitate them (additionally, it also causes many of the same motor skill impairments as alcohol, such as slurred speech and loss of balance/coordination.) Cocaine causes numbness at the point of ingestion, and it and speed both cause hyperactivity, even cardiac arrest.

Different drugs act in very different ways with very different effects, hence each is divided into one (or more) of various descriptive classes. Note, once again, none of the preceding is meant to instruct or endorse recreational use of any drugs, legally or otherwise. I consider the mind a far more entertaining plaything than the body, but neither is really a toy.