César Gaviria, who famously battled drug kingpin Pablo Escobar as Colombia’s president during a bloody chapter of the country’s fight against drug trafficking, has some advice for Philippine president Rodrigo Duterte: It’s not a war you win by sending in troops.

“Trust me, I learned the hard way,” he wrote in a New York Times opinion column Feb. 7.

Like Gaviria in the early 1990s, Duterte is in the throes of a brutal crusade against illegal drug use. The combative president recently said he would enlist the military to combat drug gangs and kill addicts. His anti-narcotics agency later clarified the army would only play a supporting role in the country’s war on drugs, though its director told Reuters the fight would result in deaths nonetheless.

As Gaviria put it in his op-ed, Colombians know a thing or two about waging war on drugs. The country has spent billions of dollars to tamp down drug trafficking by force, and Gaviria oversaw the capture of Escobar in 1993. That tough-on-drugs approach is an alluring one for politicians given its popularity with the public, said Gaviria. He admitted being seduced by it himself.

But that strategy ultimately failed in Colombia, he wrote. He went further: cracking down on drugs makes the problem worse, pushing consumers into crime. “The war on drugs is essentially a war on people,” he wrote.

Instead, he recommended that the Philippines, and other countries in a similar situation, focus on rooting out corruption, providing access to public health, and legalizing certain drugs.

“No matter what Mr. Duterte believes,” he said, “there will always be drugs and drug users in the Philippines.”