Tirzepatide, sold as Zepbound, is currently the most effective prescription drug for weight loss. In a meta-analysis directly comparing the two leading medications, tirzepatide produced about 4.6% more body weight loss than semaglutide (Wegovy), which itself significantly outperforms older options. But “best” depends on more than raw efficacy. Cost, side effects, how you take the medication, and whether you even qualify for a prescription all factor into which drug makes the most sense for you.
How the Top Medications Compare
Five prescription medications are currently approved for long-term weight management in the U.S. They fall into two tiers based on how much weight people typically lose.
The top tier includes the two weekly injectables: tirzepatide (Zepbound) and semaglutide (Wegovy). In clinical trials, semaglutide produced an average of 13.7% body weight loss over a year, while phentermine/topiramate, the next best option, achieved 9.1%. Tirzepatide goes further still. In head-to-head comparisons, people on tirzepatide were more than twice as likely to lose 15% or more of their body weight compared to those on semaglutide. For someone weighing 250 pounds, that gap could mean the difference between losing 34 pounds and losing 46.
The second tier includes two oral medications. Phentermine/topiramate (Qsymia) produces roughly 5% weight loss from baseline at one year, with about a 9% average in some analyses. Bupropion/naltrexone (Contrave) performs similarly, averaging around 4.6% weight loss. These are daily pills rather than injections, which matters to people who want to avoid needles. They produce meaningful results, just not on the same scale as the newer injectables.
Why the Newer Drugs Work So Well
Semaglutide mimics a gut hormone called GLP-1 that your body naturally releases after eating. It activates receptors in the brain’s appetite control center, creating a strong feeling of fullness and reducing food cravings. It also slows how quickly food leaves your stomach, so you feel satisfied longer after meals.
Tirzepatide activates two hormone pathways instead of one. It targets both the GLP-1 receptor and the GIP receptor, which appears to work through a separate set of neurons in the same brain region. This dual action likely explains the extra weight loss. Interestingly, GIP receptor activation may also dampen some of the nausea signals triggered by GLP-1, potentially making the medication more tolerable for some people at higher doses.
The older oral medications work through entirely different pathways. Phentermine/topiramate combines a stimulant that suppresses appetite with a compound that alters how the brain processes signals related to satiety. Bupropion/naltrexone pairs an antidepressant with an opioid-blocking agent to reduce the reward response to food. These mechanisms are less targeted than the hormone-based approach, which partly explains the smaller effect size.
What the Side Effects Look Like
Gastrointestinal problems are the main downside of GLP-1 based medications. Across large studies, the overall rate of digestive side effects runs about 12%, with nausea being the most common at roughly 21% of users. Vomiting affects about 9%, diarrhea about 11%, and constipation about 8%. For most people, these symptoms are worst during the first few weeks and during dose increases, then gradually fade.
Both Zepbound and Wegovy use a slow dose escalation specifically to minimize these effects. Wegovy starts at a low 0.25 mg weekly injection and steps up over several months to a maintenance dose of up to 2.4 mg. Zepbound begins at 2.5 mg weekly and increases to a range of 5 to 15 mg. The gradual ramp gives your body time to adjust. Serious complications like bowel obstruction are rare and tend to occur in people who already have digestive motility issues.
The oral medications carry their own side effect profiles. Phentermine/topiramate can cause tingling in the hands and feet, dry mouth, and taste changes. Because it contains a stimulant, it can raise heart rate. Bupropion/naltrexone commonly causes nausea and headache, and it carries a warning about seizure risk at high doses. All weight loss medications have higher discontinuation rates than placebo due to side effects.
Who Qualifies for a Prescription
Prescription weight loss medications are approved for adults with a BMI of 30 or higher, or a BMI of 27 or higher if you also have a weight-related health condition like high blood pressure or type 2 diabetes. A BMI of 30 corresponds to about 210 pounds for someone who is 5’9″.
Your doctor will also consider your medical history. People with a personal or family history of a specific type of thyroid cancer should not take tirzepatide or semaglutide. Those with a history of pancreatitis need careful evaluation. And if you have a seizure disorder, bupropion/naltrexone is typically off the table.
Injectable vs. Oral Options
If needles are a dealbreaker, oral semaglutide exists but currently produces less weight loss than the injectable version. In real-world studies, the injectable form led to about 4% body weight loss at six months compared to roughly 3.7% for the oral form at the doses currently available for diabetes. Around 55% of people on injectable semaglutide achieved clinically significant weight loss of 5% or more, compared to 39% on the oral version. Higher-dose oral formulations designed specifically for weight loss are in the pipeline and may close that gap.
The two older options, phentermine/topiramate and bupropion/naltrexone, are both daily pills. They produce less dramatic results than the injectables but offer a needle-free alternative that still beats lifestyle changes alone.
What These Medications Cost
Cost has been the biggest barrier to access. Wegovy has listed at around $1,350 per month and Zepbound at about $1,086 per month without insurance or discount programs. The older oral medications cost significantly less but still run several hundred dollars monthly without coverage.
Pricing is shifting rapidly. Recent federal negotiations have brought the price of Wegovy and Zepbound down to roughly $350 per month through certain government programs, with Medicare beneficiaries paying a copay of $50 per month. Medicare will now cover these medications for obesity with related health conditions for the first time. State Medicaid programs are also gaining access at reduced prices. If an oral version of Wegovy receives approval, its initial price through government channels would be $150 per month.
Private insurance coverage varies widely. Some plans cover weight loss medications with prior authorization, while others exclude them entirely. Even with coverage, copays can be steep. It’s worth checking your specific plan and asking about manufacturer savings cards, which can dramatically reduce out-of-pocket costs for commercially insured patients.
What Happens When You Stop
Weight regain after stopping these medications is common across all options. The hormonal signals that drove appetite reduction return, and most people regain a significant portion of lost weight within a year of discontinuation. This is not a personal failure. It reflects the biology of weight regulation. For this reason, many clinicians now view these medications as long-term treatments rather than short courses, similar to how blood pressure medications manage hypertension without curing it. That makes the monthly cost and side effect tolerance especially important in choosing which drug fits your life.