Which Weight-Loss Injection Is Best for Women?

Tirzepatide has the strongest head-to-head evidence for weight loss. In a 72-week trial it beat semaglutide, with an average loss of 20.2% of body weight against 13.7%. Semaglutide has the longest track record and tends to cost less. Retatrutide is the newest option, with the largest results in its own trials but no head-to-head test yet. The one that fits you depends on how much you want to lose, how your stomach handles the medicine and your budget. Our clinical team decides which one is right for you.

Which weight-loss injection works best?

Tirzepatide is the only one of the three that has beaten another in a direct trial. In the SURMOUNT-5 head-to-head trial of 751 adults with obesity and no diabetes, people on tirzepatide lost an average of 20.2% of their body weight over 72 weeks. People on semaglutide lost 13.7%. Each person was on the highest dose they could tolerate. Waists shrank by 18.4 cm with tirzepatide and 13.0 cm with semaglutide, which is the difference you notice when your jeans fit again. Eli Lilly, which makes tirzepatide, funded the trial.

A pooled review of the head-to-head studies found the same thing. On tirzepatide, people were more likely to lose at least 10%, 15% and 20% of their weight. At 5%, there was no difference between the two. If your goal is a smaller loss, both get there. If you want a bigger loss, tirzepatide had the edge.

Retatrutide's numbers come from its own trials. In an 80-week phase 3 trial of adults with obesity and no diabetes, average weight loss was 17.6% on 4 mg, 23.7% on 9 mg and 25.0% on 12 mg, against 3.9% on placebo. Those are the largest figures of the three. It has not been tested head to head against tirzepatide or semaglutide, though, so no one can yet say it beats either one. A 2026 review noted that retatrutide did not yet have FDA approval for obesity. Your clinical team can tell you whether it makes sense for you.

What about women specifically? The big trials report average results for everyone. The research here does not show tirzepatide and semaglutide results split by sex, so nobody can say from these trials which of the two works better for women. Retatrutide is the exception. In its earlier phase 2 trial, planned analyses found that women lost a larger percentage of their weight than men. That finding applies to retatrutide only, not to the other two.

Which injection has the worst side effects?

On serious side effects, tirzepatide comes out worse than semaglutide in the head-to-head data. Stomach side effects are the most common problem with all three: nausea, vomiting, diarrhea and constipation. In the head-to-head trial, they were mostly mild to moderate and showed up mainly while the dose was going up.

The pooled review shows the trade-off. Serious adverse events happened in 5.7% of people on tirzepatide and 2.9% on semaglutide. Overall and stomach-related side effects were similar between the two. The share of people who stopped because of side effects was 7.2% on tirzepatide and 5.5% on semaglutide, which was not a significant difference. So the bigger weight-loss result came with a higher rate of serious events. Ask your clinical team what to watch for.

Retatrutide followed the same pattern in its phase 2 trial. Stomach side effects came during dose increases and were more frequent at higher doses. Starting at 2 mg instead of 4 mg eased them partly. Heart rate went up as the dose went up and peaked at 24 weeks.

The Wegovy (semaglutide) label carries a boxed warning about thyroid C-cell tumors seen in rodents. It says not to use Wegovy if you or a family member has had medullary thyroid carcinoma, a type of thyroid cancer, or MEN 2, an inherited condition that causes tumors in hormone glands. On the label, severe stomach reactions happened in 4.1% of people on Wegovy against 0.9% on placebo. The label also says to stop it 2 months before you plan to get pregnant. Tell your clinical team about any of this history and any pregnancy plans. Do not assume the Wegovy label applies in the same way to tirzepatide or retatrutide.

Pushing through has a cost. One person in r/Zepbound, in a thread called "Throwing in the towel," wrote: "I started at the lowest dose (2.5 mg), and never increased, due to side effects." They stopped after two months and two ER trips. They also wrote, "The good in all this, I lost 23 lbs and I got really great at counting calories." Their advice: "Listen to your body while it whispers, before it starts to yell." If side effects start, tell your clinical team early.

Will I lose muscle on a weight-loss injection?

Yes, some of the weight you lose is muscle. That matters if you want to look lifted and not only smaller. A review of seven trials with 821 people found an average drop in lean mass of 1.74 kg. Lean mass still went up as a share of total body weight, by 1.81%, because people lost more fat than muscle. Earlier analyses estimated that lean mass makes up about 25% of the weight lost.

Most of the trials in that review were of liraglutide, an older drug, with one semaglutide study and one tirzepatide study. Semaglutide showed the largest lean mass loss, 5.44 kg over 52 weeks. The tirzepatide trial did not report a breakdown, so it could not be pooled, and the review had no muscle data for retatrutide. That means no one can say from this review which injection protects muscle best.

The fix is the same for all three. The authors say the medicine should come with nutrition and exercise to keep or build muscle. Ask your clinical team how to fit strength training and enough protein into your plan.

How much do weight-loss injections cost?

Tirzepatide usually costs more than semaglutide. A Merriwell Research survey of telehealth providers that post their prices found:

• Compounded semaglutide: $99 to $348 a month, with a median of $175, across 16 providers.
• Compounded tirzepatide: $129 to $359 a month, with a median of $237, across 14 providers.
• 13 of the 14 providers charged more for tirzepatide than for semaglutide.

Read the fine print on plans. At the 12 providers that posted both prices, paying month to month cost 1.11 to 2.2 times the rate for their longest plan, with a median of 1.63 times. Three providers added a required membership or care fee that raised the monthly bill by $49 to $99.

Compounded medicines are not the same as the brand-name drugs. They are not FDA-approved, and the FDA does not review them for safety or effectiveness. The trial results on this page come from brand-name products. Our clinical team can explain what applies to your prescription.

Which weight-loss injection fits me?

• You want to lose as much as possible, with a head-to-head win behind it: ask about tirzepatide. In the pooled data it led to more weight loss and made bigger losses more likely. Serious side effects were also more frequent, so talk them through with your clinical team.
• You want the longest track record and usually a lower monthly price: ask about semaglutide. It had fewer serious side effects than tirzepatide in the head-to-head data. Its average loss in that trial was 13.7% against 20.2%, and 13.7% of your body weight is still a big change.
• You have a lot to lose, or have not got far on the others: ask whether retatrutide is worth discussing. It has the largest numbers in its own trials, an average of 25.0% on the 12 mg dose. It is newer, has not been compared directly with the other two and did not yet have FDA approval for obesity in the 2026 review. Our clinical team decides whether it fits.
• Your stomach is sensitive: tell your clinical team before you start. The dose goes up slowly, and in the retatrutide trial a lower starting dose cut down on stomach side effects. Starting low is a choice you make with your clinical team, not a failure.
• Whichever one you choose: plan for muscle. Set up strength training and enough protein with your clinical team so the weight you lose is mostly fat.
• Before you start: tell your clinical team about thyroid cancer in your family, pregnancy plans, pancreas or kidney problems and everything else you take. Our clinical team reviews your answers and decides what fits.

The quiz asks about your goal, your history and what you have tried. That lets our clinical team see whether semaglutide, tirzepatide or retatrutide fits the way you want to lose weight and keep your shape. Take the quiz to start your plan.