It’s normally safe to assume that any pill promising weight loss is, at best, a gimmick. Or at worst, harmful.

So it’s no wonder that readers were surprised when we reported that obesity specialist Spencer Nadolsky, D.O., uses appetite suppressants to help his patients drop pounds.

As it turns out, the Food and Drug Administration has approved four prescription medications for weight loss in the last three years: Qsymia, Belviq, Contrave, and Saxenda.

If you’re looking to shave off the last few pounds, these meds are not for you. They’re recommended only for people whose body mass indexes put them firmly in the “overweight” or “obese” categories.

Related: Why Dwayne ‘The Rock’ Johnson Is Technically Obese

The drugs work on receptors in your brain to dull your appetite. They address the obvious, but frequently overlooked, problem that keeps many people fat: Genuine hunger.

“Most people fail at losing weight,” Nadolsky said. “They fail because they can’t stick to it long term, and a lot of that has to do with hunger.”

Having excess fat on your frame can actually disrupt the hunger signals in your brain, he says, so that you feel hungrier than other people do.

The pills aren’t magic: You still have to eat right and exercise to lose weight on them. They just prevent you from feeling starving and miserable while you cut back, which makes the effort more sustainable, he said.

(For a drug-free weight-loss program that won’t leave you feeling hungry, check out Lose Your Spare Tire.)

In clinical trials, the drugs helped most people lose about 5 percent of their body weight or more. But Nadolsky has seen more dramatic results in his practice, he says, with some patients dropping up to 100 pounds.

As with any medication, each of these four are associated with possible side effects—one reason why they’re prescribed only to people who need to lose weight for health reasons.

Plus, you may have to stay on the drugs forever: Most people who stop taking them regain the weight they lost, Nadolsky said.

Think you’re a candidate? Ask your primary care doctor. The meds are still new and not yet widely used, Nadolsky said, so some physicians may not be familiar or on board with them. You can find a list of doctors who specialize in obesity medicine at ABOM.org.

And remember to try non-prescription methods to curb your appetite first, like getting protein and fat at every meal, filling up on vegetables, and eating slowly, Nadolsky said.