From Dmitri Tymoczko's 1996 article on William James:

Americans it is often remarked, are confused about drugs. The image of William Bennett giving up his cigarettes in order to lead the nation's War on Drugs exemplifies this confusion. We tolerate cigarettes and alcohol but prohibit the recreational use of similarly mild intoxicants, including marijuana. We pour billions of dollars into law enforcement but devote only a tiny fraction of this amount to the medical treatment and rehabilitation of drug addicts. Courts impose widely disparate punishments for the possession and use of chemically similar substances, notably crack and powdered cocaine. But perhaps the most egregious area of inconsistency involves religious drug use. Faced with the claim that drug use contributes importantly to religious belief, courts have made a number of confused and conflicting judgments. [...]

The reasoning behind decisions that uphold the right to use drugs in a religious context is obvious: drugs play an important, even essential, role in the practice of many religious groups; the Constitution protects the free exercise of religious belief; therefore the Constitution protects the use of drugs. The reasoning behind decisions that reject the same right is that religious action, unlike religious belief, is not absolutely protected by the Constitution. The distinction was definitively articulated by Justice Owen Roberts in Cantwell v. Connecticut (1940). "The [First] Amendment," he wrote, "embraces two concepts--freedom to believe and freedom to act. The first is absolute but, in the nature of things, the second cannot be." Thus the law, though it does not seek to prevent people from having certain religious beliefs, may prevent them from acting on those beliefs. Courts have held, for instance, that prohibitions on polygamy apply to Mormons, and that even Christian snake-handling sects are subject to regulations controlling the treatment of dangerous animals. Since taking drugs is an action, it is thus subject to government regulation.

But is this the right way to look at the situation? William James used drugs not because he had religious beliefs that encouraged him to do so but in order to generate religious or mystical beliefs that he otherwise would not have had. [...]

More important, James's philosophy gives us a principled way to think about the relation between religion and drugs. From a Jamesian perspective, religious toleration represents not just a commitment to individual freedom, not simply a hands-off policy on the part of the government toward questions of ultimate truth, but rather an affirmative decision to shelter certain useful though potentially false beliefs. Drug use, from this perspective, represents a similar sort of decision, but on the level of the individual rather than of the society. Just as a society might choose to nurture or tolerate certain sorts of illusions, pluralistically embracing both atheistic and religious subcultures, so, too, might an individual decide--as did James--to divide his or her life into periods of sober rationality and ecstatic religious intoxication. Drugs can allow even the most skeptical people, those who by constitution or upbringing are not susceptible to religious insights, to experience temporary periods of pleasing falsehood. Indeed, this is the real religious significance of drug use, from the Jamesian point of view--that it lets us choose, if only vaguely and temporarily, what to believe.