What pharmacologists cannot make sense of is that people who are high on marijuana cannot be shown, in objective terms, to be different from people who are not high. That is, if a marijuana user is allowed to smoke his usual doses and then to do things he has had a chance to practice while high, he does not appear to perform any differently from someone who is not high. Now, this pattern of users performing better than nonusers is a general phenomenon associated with all psychoactive drugs. For example, an alcoholic will vastly outperform a nondrinker on any test if the two are equally intoxicated; he has learned to compensate for the effects of the drug on his nervous system. But compensation can proceed only so far until it runs up against a ceiling imposed by the pharmacological action of the drug on lower brain centers. Again, since marijuana has no clinically significant action on lower brain centers, compensation can reach 100 percent with practice.