The injectable weight loss drugs you’ve been hearing about are a class of medications called GLP-1 receptor agonists. The two most prominent are Wegovy (semaglutide) and Zepbound (tirzepatide), both FDA-approved for chronic weight management. They’re given as once-weekly shots under the skin using a pen device, and in clinical trials they’ve produced weight loss of 15% to 21% of body weight over about a year and a half.
How These Drugs Work
Your gut naturally releases hormones after you eat that signal fullness to your brain and help regulate blood sugar. These injectable drugs mimic those hormones, specifically one called GLP-1. Zepbound goes a step further by also mimicking a second gut hormone called GIP. The result is a powerful reduction in appetite: you feel full sooner, stay satisfied longer, and think about food less often throughout the day.
The effects aren’t just in your head. These drugs also slow how quickly food leaves your stomach, which extends that feeling of fullness after meals. They improve blood sugar control by boosting insulin release and dialing back the hormone that raises blood sugar. Together, these central and peripheral effects create a significant shift in how much you eat without requiring constant willpower.
Wegovy vs. Zepbound
Wegovy, made by Novo Nordisk, was the first weekly injectable to gain widespread attention for weight loss. In the landmark STEP 1 trial, participants lost an average of 14.9% of their body weight over 68 weeks, compared to just 2.4% for those on placebo. The maintenance dose is 2.4 mg once weekly, and you start at a much lower dose of 0.25 mg, increasing every four weeks to give your body time to adjust.
Zepbound, made by Eli Lilly, arrived in late 2023 and targets both GLP-1 and GIP receptors. In the SURMOUNT-1 trial, people on the highest dose (15 mg) lost an average of 20.9% of their body weight over 72 weeks. That’s roughly a fifth of total body weight, which for someone starting at 250 pounds would mean losing about 52 pounds. The dose starts at 2.5 mg and is gradually increased over 4 to 20 weeks, with target maintenance doses of 5 mg, 10 mg, or 15 mg weekly depending on response and tolerability.
An older injectable option called Saxenda (liraglutide) still exists but requires daily injections and produces less weight loss than either weekly option. Most prescribers now favor the newer drugs.
Who Qualifies
The FDA approved these medications for adults with a BMI of 30 or higher (which meets the clinical definition of obesity) or a BMI of 27 or higher if they also have at least one weight-related health condition. Qualifying conditions include high blood pressure, type 2 diabetes, high cholesterol, sleep apnea, fatty liver disease, and osteoarthritis.
In practice, getting a prescription can be more complicated than meeting the FDA label. Many insurance plans and health systems set their own, often stricter, thresholds. Some require a BMI of 35 or even 40 before they’ll cover the medication. Others require documentation that you’ve tried diet and exercise programs first. The gap between who the FDA says can use these drugs and who can actually access them remains significant.
What the Side Effects Feel Like
Gastrointestinal issues are by far the most common side effects, and the slow dose escalation exists specifically to minimize them. Nausea is the one most people experience, affecting roughly 22% of semaglutide users and 25% of tirzepatide users across clinical data. It tends to be worst in the first few weeks at each new dose level and often fades as your body adjusts. Vomiting occurs in about 9% of users of either drug. Diarrhea, constipation, and reduced appetite round out the typical list.
Most GLP-1 drugs carry a boxed warning about thyroid tumors. In animal studies, these medications caused thyroid cell growths, and while the risk in humans is not clearly established, the FDA considers it serious enough to flag prominently. People with a personal or family history of a specific type of thyroid cancer called medullary thyroid carcinoma should not use these drugs.
What It Costs
Without insurance, these medications are expensive. Zepbound’s list price ranges from $499 to about $1,086 per monthly supply (four pens), depending on the dose. Eli Lilly also offers direct-to-patient pricing for certain doses, starting at $299 per month for the lowest 2.5 mg dose and going up to $699 for the 10 mg, 12.5 mg, and 15 mg doses. For people with commercial insurance that doesn’t cover Zepbound, a savings program may bring the cost to $499 per month.
Wegovy’s retail price is in a similar range, typically around $1,300 per month at list price, though manufacturer coupons and insurance coverage can reduce that substantially. Coverage varies widely between plans. Medicare currently does not cover these drugs for weight loss, though legislation to change that has been proposed. If cost is a barrier, your prescriber’s office can often help navigate savings programs or prior authorization appeals.
What to Expect on Treatment
You inject the medication yourself using a prefilled pen, typically in your abdomen, thigh, or upper arm. The needle is small and the injection takes only a few seconds. Most people pick the same day each week and can choose any time of day regardless of meals.
Weight loss is not immediate. The first month or two are spent on lower “ramp-up” doses designed to let your digestive system adapt, and meaningful weight loss usually begins once you reach the higher doses. Most of the weight loss in clinical trials occurred over the first 60 to 68 weeks, with results plateauing after that. The drugs work best alongside changes to diet and physical activity, and in trials, all participants received lifestyle counseling in addition to the medication.
One important reality: the weight tends to come back if you stop the medication. Studies tracking participants after discontinuation consistently show significant weight regain. For most people, these drugs are effective as long-term, potentially indefinite, treatment rather than a short course that permanently resets your weight.