Liberty protects the person from unwarranted government intrusions into a dwelling or other private places. In our tradition the State is not omnipresent in the home. And there are other spheres of our lives and existence, outside the home, where the State should not be a dominant presence. Freedom extends beyond spatial bounds. Liberty presumes an autonomy of self that includes freedom of thought, belief, expression, and certain intimate conduct.
-- Lawrence v. Texas
Some constitutions expressly secure what the U.S. Supreme Court, following general recognized principles well accepted by the general public, has deemed to be secured by implication of general terms and principles.* For instance, the constitution of Argentina:
The private actions of men which in no way offend public order or morality, nor injure a third party, are only reserved to God and are exempted from the authority of judges. No inhabitant of the Nation shall be obliged to perform what the law does not demand nor deprived of what it does not prohibit.
Thus, in Argentina courts have spoken of the "right to privacy personal autonomy" and "the ability to conduct its life, decide on the best way to do it, self-reliance and tools for this purpose, selected and used with autonomy, which is a pledge of maturity and condition of freedom," while noting that the "state cannot establish morality." The limit is "as long as it doesn't constitute clear danger." The immediate source of these quotes (in translated from) comes from a recent ruling that secured the right to use small amounts of marijuana. The Alaska Supreme Court did the same in the 1970s.
As the articles discuss, there is a growing effort in Latin America and some nations in Western Europe (Glenn Greenwald has discussed his study of the efforts in Portugal) to bring forth a new drug policy, one that finds the criminal approach counterproductive. As the ruling here once notes, it "does not seem unreasonable hold that a State's punitive response to consumer translates into a re-victimization." This does not mean necessarily legalization, though that might be the path in some places for marijuana. But, it does suggest a push toward treatment and civil policies:
It followed Mexico's decision to stop prosecuting people for possession of relatively small quantities of marijuana, cocaine, heroin and other drugs. Instead, they will be referred to clinics and treated as patients, not criminals.
An ideal regime might be to allow the personal use of various types of drugs. Again, when small amounts of marijuana and various other drugs (including for religious or health uses) is involved, even civil penalties can be inappropriate. But, as a general matter, particularly given various forces (Portugal was restrained in part by treaty obligations that rejected legalization of drugs, particularly involving international commerce), a sane policy can provide a middle path. This includes, at the bare minimum, some sanity as to criminal penalties and clean needle programs.
As the Supreme Court has noted: "The opinion of the world community, while not controlling our outcome, does provide respected and significant confirmation for our own conclusions." Some seem not to think this too relevant, or are convinced by fictional analysis of actual practice in respect to health care. Such closed minded ignorance is dubious there and the same can be applied here.
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* For instance, the "moral fact that a person belongs to himself, and not others nor to society as a whole" is a core aspect of "liberty" protected by the Due Process Clause (or Ninth Amendment, if you like).