In my experience, good public policy is best shaped by the dispassionate analysis of what in practice has worked, or not. Policy based on common assumptions and popular sentiments can become a recipe for mistaken prescriptions and misguided interventions.

Nowhere is this divorce between rhetoric and reality more evident than in the formulation of global drug policies, where too often emotions and ideology rather than evidence have prevailed.

Take the case of the medical use of cannabis. By looking carefully at the evidence from the United States, we now know that legalizing the use of cannabis for medical purposes has not, as opponents argued, led to an increase in its use by teenagers. By contrast, there has been a near tripling of American deaths from heroin overdoses between 2010 and 2013, even though the law and its severe punishments remain unchanged.

This year, between April 19 and 21, the United Nations General Assembly will hold a special session on drugs and the world will have a chance to change course. As we approach that event, we need to ask ourselves if we are on the right policy path. More specifically, how do we deal with what the United Nations Office on Drugs and Crime has called the "unintended consequences" of the policies of the last 50 years, which have helped, among other things, to create a vast, international criminal market in drugs that fuels violence, corruption and instability? Just think of the 16,000 murders in Mexico in 2013, many of which are directly linked to drug trafficking.

A War on People

Globally, the "war on drugs" has not succeeded. Some estimate that enforcing global prohibition costs at least $100 billion (€90.7 billion) a year, but as many as 300 million people now use drugs worldwide, contributing to a global illicit market with a turnover of $330 billion a year, one of the largest commodity markets in the world.

Prohibition has had little impact on the supply of or demand for drugs. When law enforcement succeeds in one area, drug production simply moves to another region or country, drug trafficking moves to another route and drug users switch to a different drug. Nor has prohibition significantly reduced use. Studies have consistently failed to establish the existence of a link between the harshness of a country's drug laws and its levels of drug use. The widespread criminalization and punishment of people who use drugs, the over-crowded prisons, mean that the war on drugs is, to a significant degree, a war on drug users — a war on people.

Africa is sadly an example of these problems. The West Africa Commission on Drugs, which my foundation convened, reported last year that the region has now become not only a major transit point between producers in Latin America and consumers in Europe, but an area where consumption is increasing. Drug money, and the criminality associated with it, is fostering corruption and violence. The stability of countries and the region as a whole is under threat.

I believe that drugs have destroyed many lives, but wrong government policies have destroyed many more. We all want to protect our families from the potential harm of drugs. But if our children do develop a drug problem, surely we will want them cared for as patients in need of treatment and not branded as criminals.

Stop Stigmatizing and Start Helping

The tendency in many parts of the world to stigmatize and incarcerate drug users has prevented many from seeking medical treatment. In what other areas of public health do we criminalize patients in need of help? Punitive measures have sent many people to prison, where their drug use has worsened. A criminal record for a young person for a minor drug offence can be a far greater threat to their well-being than occasional drug use.

The original intent of drug policy, according to the UN Convention on Narcotic Drugs, was to protect the "health and welfare of mankind." We need to refocus international and national policy on this key objective.

This requires us to take four critical steps.

First, we must decriminalize personal drug use. The use of drugs is harmful and reducing those harms is a task for the public health system, not the courts. This must be coupled with the strengthening of treatment services, especially in middle and low-income countries.

Second, we need to accept that a drug-free world is an illusion. We must focus instead on ensuring that drugs cause the least possible harm. Harm reduction measures, such as needle exchange programs, can make a real difference. Germany adopted such measures early on and the level of HIV infections among injecting drug users is close to 5 percent, compared to over 40 percent in some countries which resist this pragmatic approach.

Third, we have to look at regulation and public education rather than the total suppression of drugs, which we know will not work. The steps taken successfully to reduce tobacco consumption (a very powerful and damaging addiction) show what can be achieved. It is regulation and education, not the threat of prison, which has cut the number of smokers in many countries. Higher taxes, restrictions on sale and effective anti-smoking campaigns have delivered the right results.

The legal sale of cannabis is a reality that started with California legalizing the sale of cannabis for medical use in 1996. Since then, 22 US states and some European countries have followed suit. Others have gone further still. A voter initiative which gained a majority at the ballot box has caused Colorado to legalize the sale of cannabis for recreational use. Last year, Colorado collected around $135 million in taxes and license fees related to legal cannabis sales. Others have taken less commercial routes. Users of Spain's cannabis social clubs can grow and buy cannabis through small non-commercial organizations. And Canada looks likely to become the first G7 country to regulate the sale of cannabis next year.

Legal Regulation Protects Health

Initial trends show us that where cannabis has been legalized, there has been no explosion in drug use or drug-related crime. The size of the black market has been reduced and thousands of young people have been spared criminal records. But a regulated market is not a free market. We need to carefully think through what needs regulating, and what does not. While most cannabis use is occasional, moderate and not associated with significant problems, it is nonetheless precisely because of its potential risks that it needs to be regulated.

And therefore, the fourth and final step is to recognize that drugs must be regulated precisely because they are risky. It is time to acknowledge that drugs are infinitely more dangerous if they are left solely in the hands of criminals who have no concerns about health and safety. Legal regulation protects health. Consumers need to be aware of what they are taking and have clear information on health risks and how to minimize them. Governments need to be able to regulate vendors and outlets according to how much harm a drug can cause. The most risky drugs should never be available "over the counter" but only via medical prescription for people registered as dependent users, as is already happening in Switzerland.

Scientific evidence and our concern for health and human rights must shape drug policy. This means making sure that fewer people die from drug overdoses and that small-time offenders do not end up in jail where their drug problems get worse. It is time for a smarter, health-based approach to drug policy.

It is time for countries, such as Germany, which have adopted better policies at home, to strongly advocate for policy change abroad. The United Nations General Assembly special session on the world drug problem would be a good place to start.

This piece first appeared on Spiegel.