There is no single “best” diet pill, but several FDA-approved prescription medications produce meaningful weight loss, and they far outperform anything you can buy over the counter. The most effective options available right now are GLP-1 medications, which can help people lose 15% to 25% of their body weight. Everything else, from older prescription pills to supplements on pharmacy shelves, falls well short of that range.
That said, what works for you depends on your starting weight, your budget, your health history, and whether you qualify for a prescription. Here’s what the evidence actually shows for each category.
Prescription Medications That Work
The strongest weight loss results come from a class of drugs called GLP-1 receptor agonists. These medications mimic a gut hormone that signals fullness to your brain, slows digestion, and reduces food cravings. Brand names you’ve likely heard include Wegovy (semaglutide) and Zepbound (tirzepatide), both of which started as injections. Wegovy recently became available in pill form as well, which is a significant shift for people who don’t want weekly shots.
Older prescription options still exist and may cost less. Phentermine is the most commonly prescribed weight loss drug in the United States. It works as a stimulant, suppressing appetite by increasing certain brain chemicals that reduce hunger. It’s generally approved only for short-term use (a few weeks to a few months). Another option combines phentermine with a second compound that further curbs appetite and makes food less rewarding. There’s also a combination pill that targets the brain’s reward centers to reduce cravings, particularly for people who tend toward emotional or compulsive eating.
Orlistat takes a completely different approach. Instead of affecting your brain, it blocks enzymes in your gut that digest fat, preventing your body from absorbing roughly 30% of the fat you eat. The undigested fat passes through your system, which is effective but comes with well-known digestive side effects (oily stools, urgency, gas) that many people find difficult to tolerate.
Who Qualifies for a Prescription
Doctors follow specific guidelines when prescribing weight loss medication. You typically need a BMI of 30 or greater, or a BMI of 27 or greater with at least one weight-related health problem such as high blood pressure or type 2 diabetes. Your doctor won’t prescribe these medications for someone looking to lose a few vanity pounds. They’re designed for people whose weight poses a genuine health risk.
What About Over-the-Counter Pills?
If you don’t qualify for a prescription or want to avoid one, the options get much weaker. A low-dose version of orlistat (sold as Alli) is available without a prescription and uses the same fat-blocking mechanism, just at a reduced strength. It’s the only OTC product with solid clinical evidence behind it, and even then, the weight loss is modest.
Caffeine does increase the rate at which your body burns calories and breaks down fat. But the real-world impact is tiny. A large study that followed over 58,000 people for 12 years found that those who increased their caffeine intake lost, on average, less than half a kilogram more than those who decreased it. That’s roughly one pound over 12 years. Caffeine pills marketed as fat burners are exploiting a real biological effect that is, in practice, almost meaningless for weight loss.
Green tea extract is another popular supplement ingredient. A review of 14 clinical trials found that green tea preparations reduced body weight by an average of about 1 kilogram (just over 2 pounds) more than placebo over 12 to 13 weeks. When researchers looked only at studies conducted outside Japan, where methodology was more consistent, that difference disappeared entirely. The effect, if it exists at all, is negligible.
Berberine, sometimes called “nature’s Ozempic” on social media, does have some evidence for blood sugar management. But experts at the Cleveland Clinic note it’s not as effective as conventional medications, and its weight loss effects are not well established. Calling it a substitute for GLP-1 drugs is a stretch.
Costs Without Insurance
Price is often the deciding factor. Wegovy and Zepbound can now be purchased directly from the manufacturers at $499 per month for people paying out of pocket. Zepbound’s lowest starter dose costs $349 per month. These prices dropped from higher list prices (Zepbound’s original list price was $1,086 per month), but they’re still a significant ongoing expense. Insurance coverage varies widely, and many plans still don’t cover weight loss medications. Older drugs like phentermine are far cheaper, often available as generics for a fraction of the cost.
OTC supplements range from $20 to $60 per month, which sounds appealing until you consider that most of them don’t produce clinically significant results.
Common Side Effects to Expect
GLP-1 medications come with frequent gastrointestinal side effects: nausea, vomiting, diarrhea, and constipation. These are the most common complaints by a wide margin, and they tend to be worst when starting the medication or increasing the dose. Most people find they lessen over time.
Less common but more serious risks with GLP-1 drugs include inflammation of the pancreas, slowed stomach emptying (gastroparesis), bowel obstruction, and gallstone attacks. Rapid fat loss from these medications can also cause visible facial changes, sometimes called “Ozempic face,” including a hollowed appearance, wrinkles, sunken eyes, and sagging skin around the jaw.
Phentermine, as a stimulant, can raise heart rate and blood pressure, cause insomnia, and produce jitteriness. Orlistat’s side effects are almost entirely digestive and directly related to eating fatty foods while taking it.
What Happens When You Stop
This is the part most people don’t hear about upfront. A large systematic review published in The BMJ found that after stopping weight loss medication, people regain weight at an average rate of about 0.4 kilograms (just under a pound) per month. Within the first year after stopping, the average regain was 4.8 kilograms (about 10.5 pounds). For people who had been on newer GLP-1 drugs specifically, the regain was even steeper: roughly 10 kilograms (22 pounds) in the first year.
The projected timeline to return to your original pre-medication weight is about 1.5 to 1.7 years after stopping treatment. This means that for most people, weight loss medications are not a short course you take and then move on from. They work while you’re on them, and the weight returns when you stop. That’s a critical factor to weigh when considering the monthly cost and the commitment involved.
Making a Practical Decision
If you have a BMI that qualifies you and your budget allows it, GLP-1 medications produce the most dramatic results of any pill or injection currently available. If cost is a barrier, older prescription options like phentermine offer more modest results at a fraction of the price. OTC supplements, despite the marketing, do not produce weight loss that most people would notice on a scale.
Whatever you choose, the medication is most effective when paired with changes in eating and activity. No pill replaces those fundamentals. It can, however, make them far easier to stick with by reducing the constant hunger and cravings that derail most diets on their own.