Several weight loss medications genuinely work, but the most effective ones require a prescription. Injectable drugs like semaglutide (Wegovy) and tirzepatide (Zepbound) produce the largest results, with clinical trial participants losing 20% to 25% of their body weight. Older prescription pills and over-the-counter supplements also show measurable effects, though on a much smaller scale. Here’s what each option actually delivers.
GLP-1 Injections: The Most Effective Option
The weight loss drugs getting the most attention right now are GLP-1 receptor agonists, a class of injectable medications that mimic a gut hormone involved in appetite and blood sugar regulation. They slow stomach emptying, reduce hunger signals in the brain, and make you feel full sooner and longer after eating. Two are currently FDA-approved specifically for weight loss.
Tirzepatide, sold as Zepbound, is the most potent. In the SURMOUNT-4 trial, participants lost an average of 20.2% of their body weight by 36 weeks, climbing to 25.3% at 88 weeks. That translates to roughly 50 to 60 pounds for someone starting at 240. Semaglutide, sold as Wegovy, typically produces slightly less weight loss but remains highly effective, with trial results generally in the 15% to 17% range over a similar period.
Both are weekly self-injections, not pills. Doses start low and increase gradually over several months to reduce side effects. Nausea is the most common complaint, affecting roughly 21% of semaglutide users and 25% of tirzepatide users in clinical trials. Diarrhea and vomiting each affect about 10% to 15% of users. These side effects tend to be worst during dose increases and often improve over time.
The major barrier is cost. List prices exceed $1,000 per month, though manufacturers have begun offering direct purchase options around $500. Medicare enrollees can expect copays around $50 per month, and newer pricing programs may bring costs down to roughly $350 for some buyers. Insurance coverage varies widely, and many plans still exclude weight loss medications entirely.
Prescription Pills That Produce Moderate Results
If injections aren’t an option, several oral prescription medications have solid evidence behind them, though none match the results of GLP-1 drugs.
Phentermine-topiramate (Qsymia) combines an appetite suppressant with a drug originally developed for seizures. Together, they reduce hunger and change how food tastes, making high-calorie foods less appealing. At the higher dose, patients lose an average of 11% of their body weight after one year. The lower dose produces 7% to 8% loss. That’s meaningful, enough to improve blood pressure, blood sugar, and joint pain, but considerably less than what the injectables deliver.
Bupropion-naltrexone (Contrave) targets the brain’s reward and craving pathways. In a pooled analysis of six trials covering more than 10,000 patients, significantly more people on the medication achieved and maintained at least 5% or 10% weight loss compared to placebo. Early response matters with this drug: people who lose at least 5% of their weight by week 16 are much more likely to keep losing and maintain results for up to four years. If you haven’t responded meaningfully by that point, your doctor will typically recommend stopping.
Orlistat (Xenical, or Alli over the counter) works completely differently. Instead of suppressing appetite, it blocks about 30% of the fat you eat from being absorbed. The unabsorbed fat passes through your digestive system, which means the most common side effects are oily stools, gas, and urgent bowel movements, especially after high-fat meals. Over a year, orlistat users lose about 5 to 11 extra pounds beyond what dieting alone produces. It’s the least dramatic option, but it’s also the only one available without a prescription in its lower-dose form.
Over-the-Counter Supplements: Mostly Disappointing
The supplement aisle is full of products claiming to burn fat or boost metabolism, and the vast majority have little or no clinical evidence behind them. The few that do show real effects produce very modest results.
Glucomannan, a water-soluble fiber derived from konjac root, is one of the better-studied options. It works by absorbing water and expanding in your stomach, creating a feeling of fullness. It also forms a gel that slows nutrient absorption and delays stomach emptying. A systematic review of randomized controlled trials found that glucomannan supplementation led to an average weight loss of about 2 pounds compared to placebo. That’s statistically significant but barely noticeable in practice, and the quality of evidence across studies was inconsistent.
Other popular supplements like green tea extract, garcinia cambogia, and conjugated linoleic acid have even weaker or more mixed evidence. None come close to what prescription medications deliver. The supplement industry is also poorly regulated, so what’s on the label doesn’t always match what’s in the bottle.
How Results Compare Side by Side
- Tirzepatide (Zepbound): ~20% to 25% body weight loss over 9 to 20 months
- Semaglutide (Wegovy): ~15% to 17% body weight loss over 12 to 16 months
- Phentermine-topiramate (Qsymia): ~7% to 11% body weight loss over 12 months
- Bupropion-naltrexone (Contrave): ~5% to 10% body weight loss over 12 months
- Orlistat (Xenical/Alli): ~3% to 5% body weight loss over 12 months
- Glucomannan supplement: ~2 extra pounds lost
What Happens When You Stop
One reality that applies to every weight loss medication: the effects tend to reverse when you stop taking it. In the SURMOUNT-4 trial, participants who switched from tirzepatide to placebo after 36 weeks regained a significant portion of their lost weight by week 88, while those who continued the drug kept losing. This pattern holds across all the prescription options. Your body’s hunger and metabolism signals don’t permanently reset just because you took a medication for a year.
This means most people who respond well to weight loss drugs face a long-term choice about continued use, which makes cost, side effects, and insurance coverage ongoing concerns rather than short-term ones. The medications work, but they work best as part of sustained changes in eating, activity, and, for many people, continued pharmacotherapy.
Choosing the Right Option
Your starting point matters. If you need to lose 20% or more of your body weight, the GLP-1 injectables are in a different league from everything else available. If you’re looking to lose a more moderate amount, or if cost and access rule out injectables, the oral prescription options still produce clinically meaningful results. Over-the-counter supplements are unlikely to move the needle in any way you’d notice.
Eligibility for prescription weight loss medications generally requires a BMI of 30 or higher, or a BMI of 27 with at least one weight-related health condition like high blood pressure or type 2 diabetes. Your doctor can help determine which medication fits your health profile, since each one carries different contraindications. Phentermine-topiramate, for example, isn’t safe during pregnancy, and bupropion-naltrexone isn’t appropriate for people with seizure disorders or opioid use.