What Is the Best Weight Loss Medicine on the Market?

Tirzepatide, sold as Zepbound for weight management, currently produces the largest weight reductions of any approved medication, followed closely by semaglutide (Wegovy). In the first head-to-head trial between the two, people taking tirzepatide lost about 20% of their body weight over 72 weeks compared with roughly 14% for semaglutide. But “best” depends on more than kilograms lost: side effects, heart health, cost, whether you can stay on it long enough for the drug to work, and what happens if you stop all factor into the decision.

How the Two Leading Drugs Compare Head to Head

Until recently, most comparisons between tirzepatide and semaglutide relied on indirect evidence, essentially lining up separate trials and squinting at the numbers. That changed with the SURMOUNT-5 trial, published in the New England Journal of Medicine, which randomized people with obesity (but without diabetes) to one drug or the other. The results were clear: tirzepatide produced an average weight reduction of about 20% at 72 weeks, while semaglutide produced about 14%. People on tirzepatide were also more likely to reach weight-loss thresholds of 10%, 15%, 20%, and even 25% of starting weight.¹

Multiple meta-analyses confirm that advantage. One pooling clinical trials and real-world data found tirzepatide delivered roughly four additional kilograms of weight loss compared with semaglutide, and the gap widened at higher doses and longer treatment durations.² Another systematic review of head-to-head studies found participants on tirzepatide had substantially higher odds of losing at least 10% of their body weight than those on semaglutide.³ A review of phase 3 trials noted that tirzepatide at its higher doses produced roughly 4 to 5 additional percentage points of weight loss compared with semaglutide, with somewhat fewer gastrointestinal side effects in the tirzepatide groups.⁴

How These Drugs Work

Semaglutide mimics a gut hormone called GLP-1. When you eat, your intestines naturally release GLP-1, which tells your brain you are full, slows how quickly your stomach empties, and helps regulate blood sugar. Semaglutide copies that signal at much higher and steadier levels than your body produces on its own. In the brain, it acts on regions that control appetite and reward, reducing hunger and the drive to eat. In the gut, it slows digestion so food sits in the stomach longer, contributing to that feeling of fullness.⁵

Tirzepatide does all of that plus something extra. It activates both the GLP-1 receptor and a second receptor called GIP. Together, these two pathways reinforce each other’s effects on metabolism, blood sugar, and fat storage. That dual action appears to be why tirzepatide outperforms single-target drugs in weight loss.⁶ Both medications are given as weekly injections, and both require gradual dose increases over several weeks to reduce side effects.

Where Older Weight Loss Drugs Stand

Before semaglutide and tirzepatide arrived, the prescription options for weight loss were modest. A large network meta-analysis of the older generation of drugs found that phentermine-topiramate came out on top, with an estimated 75% of participants losing at least 5% of body weight compared with about 23% on placebo. Liraglutide (a lower-dose GLP-1 drug, the predecessor to semaglutide) came second at about 63%, followed by naltrexone-bupropion at 55%, lorcaserin at 49%, and orlistat at 44%.⁷ Lorcaserin has since been withdrawn from the market over cancer concerns.

A more recent network meta-analysis incorporating semaglutide placed it at the top of this broader landscape, with an average of about 9 kg more weight loss than placebo at 12 months, roughly on par with phentermine-topiramate (about 8 kg) but with lower odds of people quitting treatment.⁸ Phentermine-topiramate remains a viable and much cheaper option for some patients, though it carries its own side-effect profile including cognitive fogginess, tingling in the hands and feet, and potential birth-defect risks.

Cardiovascular Benefits Beyond the Scale

Weight loss on its own tends to improve heart health, but semaglutide appears to offer cardiovascular protection that goes beyond what the number on the scale would predict. The SELECT trial enrolled over 17,600 people with obesity and established heart disease but without diabetes. Over a median follow-up of about three years, semaglutide cut the risk of a major cardiovascular event (heart attack, stroke, or cardiovascular death) by 20% compared with placebo.⁹ A meta-analysis pooling several randomized trials confirmed that finding, reporting about a 19% reduction in major cardiovascular events.¹⁰

This is a meaningful distinction because no equivalent large-scale cardiovascular outcomes trial has been completed for tirzepatide in people without diabetes. Tirzepatide likely has heart benefits too, given the overlap in mechanisms and the magnitude of weight loss, but the hard trial data showing reduced heart attacks and strokes exists so far only for semaglutide. For someone with established cardiovascular disease, that trial evidence could tip the decision toward semaglutide despite its smaller weight-loss numbers.

Liver Health and Sleep Apnea

Fatty liver disease, now commonly called metabolic-associated steatotic liver disease, affects a large share of people with obesity. GLP-1 drugs have shown consistent improvements in liver fat, liver enzyme levels, and markers of scarring (fibrosis) in these patients. Semaglutide and liraglutide have the most data here, with tirzepatide showing promise but with less published evidence on liver-specific outcomes so far.¹¹¹²

Obstructive sleep apnea is another condition tightly linked to excess weight. A meta-analysis of GLP-1 drugs in patients with sleep apnea found a significant drop in breathing interruptions per hour, along with substantial weight loss and lower blood pressure.¹³ For people dealing with these related conditions, the weight loss drug is effectively treating multiple problems at once.

Side Effects You Should Expect

Nausea, vomiting, diarrhea, and constipation are the most common side effects across all GLP-1-based medications. These typically emerge during the dose-escalation period, when the body is adjusting to the drug, and tend to improve after a few weeks at a stable dose.¹⁴ Eating smaller meals, avoiding high-fat foods, and not lying down immediately after eating can help. Starting at the lowest dose and going up gradually, as the prescribing protocols already require, is the single most important strategy for managing GI discomfort.¹⁵

Rarer but more concerning risks exist. A pharmacoepidemiologic study found that GLP-1 drugs used for weight loss were associated with higher rates of pancreatitis, bowel obstruction, and gastroparesis compared with another weight-loss medication (naltrexone-bupropion), though the absolute risk of each remained low.¹⁶ A comprehensive review noted that evidence for some of these rarer complications is mixed, with different studies reaching different conclusions about severity and frequency.¹⁷ The takeaway: these are not risk-free drugs, and anyone with a history of pancreatitis or gallbladder disease should discuss those risks carefully with their doctor.

What Happens When You Stop

This is the uncomfortable reality of current weight-loss medications: weight comes back when you stop taking them. In the STEP 1 trial extension, people who had lost weight on semaglutide and then stopped regained about two-thirds of what they had lost within a year of discontinuation.¹⁸ A narrative review found this pattern held regardless of which drug was used or how long treatment lasted, with weight rebounding rapidly after cessation of any GLP-1 or dual-agonist therapy.¹⁹

A systematic review and meta-analysis quantified the rebound: among people with obesity who stopped their GLP-1 drug, average weight regain was about 5.6 kg, with blood sugar, waist circumference, and blood pressure also worsening. The regain was more pronounced with longer follow-up and was actually greater after stopping semaglutide than after stopping liraglutide, likely because semaglutide produces larger initial losses that create a steeper rebound.²⁰ This means that for most people, the medication is a long-term or even lifelong commitment if they want to maintain results.

The Muscle Loss Question

Whenever someone loses a large amount of weight quickly, some of that loss comes from lean tissue, including muscle. This has been a persistent concern with the new drugs. An analysis of the STEP 1 trial found that semaglutide reduced total fat mass by about 19% and visceral fat by about 27%, but lean body mass also dropped by roughly 10%. The silver lining: because fat was lost at a faster rate, the ratio of lean mass to fat mass actually improved, and the proportion of body weight made up by lean tissue went up.²¹

Research in mice has found that semaglutide reduces muscle size and strength to a similar degree as simply eating fewer calories, suggesting the muscle loss is a consequence of the calorie deficit rather than something the drug does directly to muscle tissue. Encouragingly, that same study found lean mass recovered after the drug was stopped.²² Experts have pointed out that some loss of lean tissue is inevitable during any significant weight loss because fat tissue itself contains water, blood vessels, and connective tissue that count as “fat-free mass” in body-composition measurements.²³ The practical advice is straightforward: resistance training and adequate protein intake during treatment help preserve muscle, and most obesity medicine specialists now recommend both alongside the medication.

Real-World Adherence Is Much Lower Than Trial Results Suggest

Clinical trial numbers paint the rosiest possible picture because participants receive the drug for free, have regular follow-ups, and are motivated volunteers. Real-world data tell a different story. A U.S. study of patients prescribed GLP-1 drugs found that roughly 70% discontinued therapy within 24 months, compared with discontinuation rates of about 23% over a similar period in controlled trials.²⁴ A UK study found that about 45% of patients stopped within the first year and nearly 65% by two years.²⁵

The reasons are predictable: cost, side effects, supply shortages, and the burden of weekly injections. This gap between trial performance and real-world sticking power is important because, as discussed above, stopping the medication leads to rapid weight regain. The theoretical “best” drug is only as good as a person’s ability to stay on it.

Cost and Insurance Barriers

At list price, both semaglutide and tirzepatide cost over $1,000 per month in the United States. A cost-effectiveness analysis of semaglutide for patients with obesity and cardiovascular disease found that at current prices, it was not considered cost-effective by conventional thresholds. When the price was hypothetically cut in half, the economics improved dramatically.²⁶ Most state Medicaid programs and Medicare do not cover weight-loss medications, and many private insurance plans impose prior authorization requirements or deny coverage altogether. This uneven access disproportionately affects people with lower incomes and racial and ethnic groups who already face higher obesity rates and worse access to care.²⁷

Generic versions of semaglutide are not expected for several years due to patent protections, though compounding pharmacies have been producing custom versions at lower prices. The FDA has taken enforcement actions related to compounded versions, and the legal and safety landscape around them keeps shifting. For many patients, the actual “best” weight loss drug is whichever one their insurance covers or they can afford.

Use in Teenagers

Semaglutide is now approved for adolescents aged 12 and older with obesity. The STEP TEENS trial showed that weekly semaglutide reduced BMI by about 16% over 68 weeks, compared with a slight increase in the placebo group. About 73% of treated teenagers lost at least 5% of body weight, versus 18% on placebo.²⁸ Gastrointestinal side effects were more common than in adults (62% versus 42% in the placebo group), and a small number of participants developed gallstones.²⁹ Tirzepatide trials in adolescents are ongoing but have not yet produced the same level of published evidence. For now, semaglutide is the established option for younger patients.

Drugs on the Horizon

The next wave of weight-loss medications pushes the approach even further. Retatrutide is a “triple agonist” that activates GLP-1, GIP, and glucagon receptors simultaneously. In a phase 2 trial, the highest dose produced about 24% weight loss at 48 weeks, numbers that exceed tirzepatide’s results at a comparable time point.³⁰ In a separate phase 2 trial in people with type 2 diabetes, retatrutide achieved nearly 17% weight loss and dramatically improved blood sugar control.³¹ Phase 3 trials are underway, and approval, if it comes, is likely still a couple of years off.

Other molecules in development are exploring oral formulations (pills rather than injections), combinations with muscle-sparing agents like myostatin inhibitors, and even longer-acting formulations that could be dosed monthly. The field is moving remarkably fast. What is “best” in 2025 may be surpassed by 2027.³²

Unexpected Effects on Alcohol and Reward Behavior

One of the more surprising findings around GLP-1 drugs has nothing to do with weight. Patients and researchers have both noticed that these medications seem to reduce the desire to drink alcohol. The mechanism appears to involve the same brain reward circuits that the drugs target for appetite: by dampening the dopamine response to pleasurable stimuli, GLP-1 drugs may blunt the rewarding feeling that alcohol provides.³³ Brain imaging studies have shown that GLP-1 drugs reduce activity in reward-processing areas when people are exposed to alcohol-related cues, and a meta-analysis of clinical data supports a real association between GLP-1 use and reduced drinking.³⁴

This is early-stage research, and no GLP-1 drug is approved for treating alcohol use disorder. But the signal is strong enough that clinical trials specifically targeting alcohol dependence are now being designed. For people who notice they have less interest in drinking after starting one of these medications, the effect appears to be real rather than imagined, and it adds to the growing picture of GLP-1 drugs as medications that reshape reward-driven behavior broadly, not just eating habits.