Again and again on the campaign trail, the presidential candidates have been faced by America’s rising concern about addiction, particularly to opioid painkillers and heroin. And from Hillary Clinton to Chris Christie, the politicians have responded by pledging their support for drug courts.

This bipartisan reaction is correct, in principle: Drug courts, which now exist in every state, can motivate people to overcome their substance-abuse problems more effectively than punishment can. But to make the courts work in practice, states need to see that they’re adequately funded and properly run.

Typically, states offer drug courts as an alternative to prison for addicts who are arrested for nonviolent crimes only: In exchange for pleading guilty, a defendant can spend a year undergoing assessment, treatment and monitoring. Crucially, this opportunity is offered under the threat of sanctions (including jail time) for not following the program.

There’s good evidence that the strategy works: Recidivism rates among people who have participated in drug courts are as much as one-quarter lower than for those who have not, and lower still for those who complete the programs. For every $1 spent on drug courts, a state saves about $2.21 on its criminal justice and corrections systems.

But states and counties have struggled to pay the courts’ upfront costs — mainly salaries for the case managers and coordinators who ensure that defendants get treatment. And with funding limited, drug courts have too few spaces to accommodate all the people who might benefit.

The federal government has pitched in by offering grants to plan, start or expand drug courts. But that funding has been minimal, and usually temporary.

For the next president to truly expand access to drug courts, he or she will need to make more federal money available.

Restrictions on eligibility further reduce the reach of drug courts. One study of recently incarcerated inmates found that more than 80 percent of those who could benefit from the courts were excluded.

Many drug courts also need better management. Consider that judges, rather than physicians or other medical professionals, determine people’s treatment. And very often judges fail to appreciate the value of so-called medication-assisted therapy in addiction treatment — the use of methadone and other alternatives to help people avoid the drugs to which they’re addicted.

Indeed, a 2013 study found that two-thirds of drug courts prevented those who had been using illegal opioids from being treated with methadone or similar medication, often on the mistaken belief that such drugs prolong addiction.

As a result, many people fail to complete their programs who otherwise could, and even face a higher risk of overdosing. The federal government said last year that it would deny grants to courts that ban such treatments, but court budgets are mainly funded by states. And they won’t provide effective treatment unless doctors are in charge.

Drug courts can be a good strategy for treating the U.S.’s twin epidemics of substance abuse and mass incarceration. But they need to be used more often, and more carefully.