Some in the field of substance abuse are openly skeptical of the results. And even treatment experts and researchers who accept the scientific soundness of the concept are troubled by its ethical implications. Why reward people for dropping habits they never should have taken up to begin with? Why use scarce treatment dollars for rewards if you can't be sure the results will last?
"As soon as you take the reward away -- if they haven't had any counseling or other treatment to go along with it -- who's to say that it would continue?" said Teri Cannon, executive vice president of Behavioral Health Services Inc., which provides treatment across Los Angeles County.
"We wouldn't do something like that because we couldn't afford to do something like that," said Marlene Nadel, director of client services for the North Hollywood center Cri-Help. "Even if we had the funds, it would not be the route we would take."
The operators of the San Francisco program, and others around the country, say addiction is such a costly problem in human and economic terms, that promising -- and relatively inexpensive -- ideas should not be rejected out of hand.
"What we're trying to teach people in the field to do is value science," said Stephen Gumbley, of the Addiction Technology Transfer Center of New England, which works with clinicians to translate research into practice. "Some of what gets in the way of translating science into practice is values. And one of the values of this is that we shouldn't be paying people to do what they're supposed to do in the first place."
Some of the resistance is related to the culture of drug treatment, he said.
"Our field can be very negative," he added. "We tend to approach treatment with punishment as opposed to stroking people."
Drug abuse seems to defy logic.
Consider a 2000 study of pregnant women trying to quit smoking. Women rewarded by vouchers for testing nicotine-free quit at more than three times the rate of those who received advice and referrals.
"The fact that a pregnant woman would discontinue substance use when offered a voucher for doing so, but not to improve the health of her fetus, is perplexing," Higgins said in a paper published last year. "After all, the vouchers are worth a pittance relative to the value of a healthy baby."
But Higgins and others say addicts are people in search of immediate gratification who discount rewards they can't quickly realize (such as a healthy baby six months down the road). Vouchers succeed in part because they replace one immediate reward -- the experience of being high -- with another, the researchers say.
Another study shows that vouchers work best when linked to a specific achievement. Higgins gave cocaine users counseling and vouchers over 24 weeks of treatment. In one group, addicts received the vouchers only if they tested drug-free. In the other, they received the vouchers regardless of their drug use. The first group did much better than the second.
The explanation may lie in the brain.
Edythe London, a professor of psychiatry and pharmacology at UCLA, has compared the brains of meth addicts and nonaddicts.
"Systems in the cortex, which are important for making decisions, were just not working very well," she said of the meth users. "They had less activity than in normal healthy people."
But meth users had hyperactivity in lower centers of the brain that control emotion and craving, London said. That partially explains why meth addicts consistently make irrational decisions, putting them in a "spiral where things get worse and worse and worse," she said. (Researchers are not sure to what extent meth addicts' brains are inherently different and to what extent meth contributes to the unusual pattern.)
The vouchers themselves don't change the brain. They simply give the person a choice that is less objectionable than "methamphetamine or nothing," London said.
Studies have shown that though rewards can be small, size does matter, at least in a relative sense. One study found that nicotine abstinence increased as rewards were raised from $0 to $12 per day. Over time, patients needed more incentive to stay off drugs.
The San Francisco program allows participants to earn up to $453.75 in vouchers if they attend every scheduled visit and test drug-free over 12 weeks. But Petry, the University of Connecticut researcher, has devised a less costly system, in which addicts with clean urine tests can draw for prizes. They win about half the time, collecting rewards ranging in value from $1 to $100. The rest of the time, their slip says, "Good job."
The chance of winning apparently is a powerful lure.