- Prescription weight loss pills may help people with obesity lose 5% to 10% of their body weight.
- The prescriptions are often reserved for those with a certain BMI or obesity-related complications.
- There is little evidence that OTC weight loss pills work, and some have harmful ingredients.
Just about anyone who’s tried it knows that losing weight is hard. When calorie restriction and cardio workouts leave you tired and hungry, anything that could hurry progress seems worth a try — especially something as easy as a pill.
When it comes to diet pills, there are two types: prescription drugs, and over-the-counter supplements. And they are not created or regulated equally.
Here’s what you need to know about each and whether they can help you lose weight.
Prescription weight loss medications proven to work
The Food and Drug Administration has approved five prescription drugs for long-term weight loss based on research about their safety and effectiveness. Only three of them are pills:
- Naltrexone-bupropion, sold under the brand name Contrave. Naltrexone and bupropion are separate medications, but researchers found that a pill that combines the two can help more with weight loss than either pill separately. Something to note, however, is that many of the studies on this pill’s weight-loss effects were sponsored by the company that manufactures this combination pill.
- Orlistat, sold under the brand names Xenical and Alli. Researchers have found that people with a BMI of 27 kg/m or greater who take orlistat for more than two months could lose 12.3 pounds on average. Interestingly, one 2012 study found that overweight soldiers who took orlistat for six months lost more fat mass but not as much lean mass compared with the placebo group.
- Phentermine-topiramate, sold under the brand name Qsymia. In a 2011 study, nearly half of participants who took one pill containing 15 milligrams of phentermine and 92 milligrams of topiramate daily lost more than 10% of their total body weight after 56 weeks. Common side effects included constipation, insomnia, and dysgeusia, a distorted sense of taste.
The FDA has also approved two injectable drugs for long-term use. They include:
- Liraglutide, sold under the brand name Saxenda. A 2017 review found that, on average, participants taking liraglutide lost 5% to 10% of their body weight. It is injected once a day, with the dose increasing gradually for the first five weeks.
- Semaglutide, sold under the brand name Wegovy. In a 2021 clinical trial, participants taking semaglutide lost nearly 15% of their body weight, on average. It is injected once a week, with the dose increasing gradually every month for the first five months.
A few other medications — most commonly phentermine — are approved for short-term use. But prescription weight loss medication isn’t for everyone. Doctors often reserve these treatments for people with a BMI of over 30 kg/m or those who have obesity-related health complications, like high blood pressure or diabetes.
These pills aren’t a perfect solution for obesity. Weight loss medications are used along with a healthy diet and exercise regimen that need to be continued after treatment. Also, side effects are common and can be severe.
Do over-the-counter weight loss pills work?
There are many diet pills available that aren’t FDA-approved or -regulated, and there is minimal evidence that they actually work.
Since over-the-counter dietary supplements don’t have to be vetted for safety or efficacy by the FDA, it’s much easier to get them onto shelves and into your medicine cabinet.
In fact, many manufacturers of weight loss supplements don’t test their products in humans before taking them to market. What’s more, the FDA has warned that some over-the-counter products contain hidden ingredients. These include prescription drugs and controlled substances like sibutramine, which was removed from the market in 2010 because it substantially increased heart rate and blood pressure.
So if you’re considering a diet pill supplement, there are a few things you might want to know first.
These types of diet pills often contain vitamins, minerals, enzymes, and herbs. The most common ingredients can be found in a database from the National Institutes of Health.
One such ingredient is Garcinia cambogia, which comes in products like Hydroxycut and Plexus Slim. It’s supposed to suppress appetite and decrease the number of fat cells your body makes. Though it’s considered “fairly safe,” there’s no evidence that it actually helps with weight loss, and excessive use has been linked to liver problems.
Other diet pills may contain chitosan, from the shells of crabs, lobsters, and shrimp. In theory, it’s supposed to bind fat in your digestive tract so your body can’t absorb it. In reality, according to the NIH, the amount of fat it binds is probably not enough to help you lose a significant amount of weight.
The most common ingredients are stimulants like caffeine, yerba mate, bitter orange, or guarana. When it comes to the data on these ingredients, there’s not a lot to suggest they help in any way with weight loss, said Katherine Zeratsky, a registered dietitian at the Mayo Clinic.
For example, a 2019 study found that rats given caffeine burned more calories than rats doing the same amount of exercise without a stimulant. But there is no evidence that the effect carries over to humans.
Theoretically, all these ingredients should help with weight loss, but it’s extremely difficult to figure out if they work, Zeratsky said. That’s because most diet pills are made up of multiple ingredients and the directions suggest you take them while having a diet that’s restrictive in calories. So it’s hard to tell whether you lost weight because of the product or because you simply ate fewer calories.
No matter what diet pill ingredient or program you’re considering, it’s critical that you talk to your pharmacist first, Zeratsky said, especially if you take other medications.
Though many of the ingredients are considered safe, they can have toxic effects at high doses. And it’s possible that they could interfere with your other medications. Your pharmacist can walk you through a cryptic ingredient list and point out any red flags.