Want people to quit smoking? Offer them money.

E-cigarettes, on their own, don’t appear to be very good at saving lives. If you really want to get smokers to quit, you need to build an incentive structure.

Consider a study published this week in the New England Journal of Medicine. The study’s authors took some 6,000 smokers enrolled in tobacco-cessation programs through their employers and randomly divided them into five groups. The first received information about the health benefits of not smoking and motivational text messaging. The second received free cessation aids, such as nicotine patches or pharmacotherapy and, if those failed, free e-cigarettes. The third received free e-cigarettes upfront. And the final two received financial incentives — worth up to $600 — if they kept from smoking.

The result six months later? Those receiving financial incentives were up to three times more likely to quit than those given free e-cigarettes.