What do we propose? Well, for one, we do not believe that military hardware, repressive policing and bigger prisons are the answer. Real reductions in drug supply and demand will come through improving public health and safety, strengthening anticorruption measures — especially those that combat money laundering — and investing in sustainable development. We also believe that the smartest pathway to tackling drugs is decriminalizing consumption and ensuring that governments regulate certain drugs, including for medical and recreational purposes.

While the Filipino government has a duty to provide for the security of its people, there is a real risk that a heavy-handed approach will do more harm than good. There is no doubt that tough penalties are necessary to deter organized crime. But extrajudicial killings and vigilantism are the wrong ways to go. After the killing of a South Korean businessman, Mr. Duterte seemed as if he might be closer to realizing this. But bringing the army in to fight the drug war, as he now suggests, would also be disastrous. The fight against drugs has to be balanced so that it does not infringe on the rights and well-being of citizens.

Winning the fight against drugs requires addressing not just crime, but also public health, human rights and economic development. No matter what Mr. Duterte believes, there will always be drugs and drug users in the Philippines. But it is important to put the problem in perspective: The Philippines already has a low number of regular drug users. The application of severe penalties and extrajudicial violence against drug consumers makes it almost impossible for people with drug addiction problems to find treatment. Instead, they resort to dangerous habits and the criminal economy. Indeed, the criminalization of drug users runs counter to all available scientific evidence of what works.

Taking a hard line against criminals is always popular for politicians. I was also seduced into taking a tough stance on drugs during my time as president. The polls suggest that Mr. Duterte’s war on drugs is equally popular. But he will find that it is unwinnable. I also discovered that the human costs were enormous. We could not win the war on drugs through killing petty criminals and addicts. We started making positive impacts only when we changed tack, designating drugs as a social problem and not a military one.

A successful president makes decisions that strengthen the public good. This means investing in solutions that meet the basic standards of basic rights and minimize unnecessary pain and suffering. The fight against drugs is no exception. Strategies that target violent criminals and undermine money laundering are critical. So, too, are measures that decriminalize drug users, support alternative sentencing for low-level nonviolent offenders and provide a range of treatment options for drug abusers. This is a test that many of my Colombian compatriots have failed. I hope Mr. Duterte does not fall into the same trap.