In the first year or so of decriminalization in Portugal, there did seem to be the increase in drug use that critics had predicted. But although the Portuguese model is often described simply as decriminalization, perhaps the more important part is a public health initiative to treat addiction and discourage narcotics use. My take is that decriminalization on its own might have led to a modest increase in the use of hard drugs, but that this was swamped by public health efforts that led to an overall decline.

Portugal introduced targeted messaging to particular groups — prostitutes, Ukrainians, high school dropouts, and so on. The Health Ministry dispatched workers into the most drug-infested neighborhoods to pass out needles and urge users to try methadone. At big concerts or similar gatherings, the Health Ministry sometimes authorizes the testing of users’ drugs to advise them if they are safe, and then the return of the stash. Decriminalization makes all this easier, because people no longer fear arrest.

So how effective are the methadone vans and prevention campaigns? I thought I’d ask some real experts: drug dealers.

“There are fewer customers now,” complained one heroin dealer in the gritty Lumiar neighborhood. Another, Joaquim Farinha, 55, was skeptical that methadone was costing him much business. “Business is still pretty good,” he said, interrupting the interview to make a sale to a middle-aged woman.

(Portugal’s drug market is relatively nonviolent and relaxed partly because of another factor: Handguns are tightly controlled.)

On balance, the evidence is that drug use stabilized or declined since Portugal changed approaches, particularly for heroin. In polls, the proportion of 15- to 24-year-olds who say that they have used illicit drugs in the last month dropped by almost half since decriminalization.