On December 23, Uruguayan President José Mujica signed a new law that fully legalizes marijuana in his country. Uruguay had already legalized possession, but the new law legalizes production and sale. This is an important victory in the fight against drug prohibition: it marks the first full legalization of an illicit drug since worldwide drug prohibition began in 1919. However, the broader and longer-term effects of the new law are far from certain.

Prohibition has proven to have little benefit, and comes with a long list of negative side effects: it generates violent, corrupt black markets that increase the use of dirty needles and the spread of HIV and other diseases; it results in civil-liberties infringements in the form of warrantless searches, racial profiling, and the unnecessary incarceration of thousands; and governments waste resources on police and prisons, and leave potential tax revenue as profit for illegal traffickers.

These consequences spring from the illegal markets for marijuana, cocaine, heroin, methamphetamine, and several other drugs. Since marijuana has already become de facto legal in many countries, its contribution to drug-related crime and corruption is more limited. Legalizing marijuana therefore addresses but one part of a larger problem, and may not reduce the negative effects of prohibition.

In fact, if marijuana legalization leads authorities to increase their enforcement efforts in other drug markets, then violence, corruption, and other ills due to prohibition may increase. It would then appear as though marijuana legalization had exacerbated the problems it claims to reduce, thereby supporting the arguments of prohibitionists.

Uruguay’s new law is very restrictive: Individuals can purchase no more than 40 grams of marijuana per month (and must register in a government database), and producers can cultivate no more than six plants unless they join growers’ clubs, which also face strict limits on production. Marijuana can only be sold in state-regulated pharmacies and cannot be exported or sold to tourists. A new Institute for the Regulation and Control of Cannabis will supervise all of this.

These restrictions on the legal market are somewhere between irrelevant and counter-productive. If marijuana users and producers have no trouble staying within these limits, then the limits themselves are irrelevant. More likely, however, these restrictions will keep the black market alive, undoing the key benefit of legalization.

Uruguay’s approach attempts to eliminate the ills of prohibition while still controlling access to marijuana. This is an impossible task. Weak controls of the legal market have minimal impact, and significant controls keep the black market active. Policymakers must accept that drug use is an individual decision — not an appropriate realm for government interference — and that restrictions on the purchase and production of marijuana are counter-productive.

It is far too soon to conclude that the argument for legalization has been won. Even in Uruguay, majority opinion still opposes legalization, and other countries — particularly the United States — may yet intervene in Uruguay’s marijuana legalization.

The United States pushed drug prohibition on the world via the Treaty of Versailles in 1919, and its role as “prohibitionist-in-chief” has continued under the UN’s drug-control treaties — which, by the way, appear to bar Uruguay from legalizing marijuana. The UN may push back against the new law.

The pendulum of public opinion currently swings toward legalization, at least in the United States. But pendulums swing in both directions. While U.S. opposition to Uruguay’s new law has so far been muted — perhaps because of recent marijuana legalizations in Colorado and Washington — the next U.S. president may take a harder line against marijuana. Recall that 14 states decriminalized marijuana in the 1970s, only to see the United States escalate its “War on Drugs” in the 1980s.

Uruguay’s new law constitutes real progress in dismantling prohibition, but it will not be a lasting victory unless supporters embrace more complete legalization, and for all drugs. Supporters should not restrict their case to claims about lower crime rates or increased tax revenue; they should also argue that, out of respect for personal freedom, policy must let individuals, not governments, decide who produces and uses drugs.