Are GLP-1 Drugs Worth It If You Lift? What They Do and Don't Replace

The short answer: GLP-1 medicines like Wegovy and Zepbound are approved to be used alongside a reduced-calorie diet and more physical activity, not instead of them. In trials, people lost more fat than lean mass, though the split varies a lot between trials. If you lift, resistance training is the main tool for keeping your strength while the scale drops. Talk to your doctor about whether one suits you.

That's the key point. Whether a GLP-1 is "worth it" is a medical decision for you and your doctor. What we can cover is what the research says about body composition, and what it means for your training.

What the regulators actually say

The FDA approved Wegovy (semaglutide) for use "in combination with a reduced calorie diet and increased physical activity".

Zepbound (tirzepatide) has the same framing: "in combination with a reduced-calorie diet and increased physical activity".

In other words, the medicine is an add-on. Diet and training are still the foundation.

In Australia, the Therapeutic Goods Administration (TGA) has approved Wegovy and Mounjaro for chronic weight management. Since 1 October 2024, pharmacies can no longer compound GLP-1 medicines. The TGA also warns against unregistered "GLP-1" products sold online, which it says may be fake or contain undisclosed ingredients.

Is the weight you lose on a GLP-1 fat or muscle?

More fat than lean mass, though the split varies a lot between trials.

In the STEP 1 body-composition substudy, 140 people (95 on semaglutide, 45 on placebo) had DXA scans at the start and after 68 weeks. On semaglutide, body weight fell 15.0%, compared with 3.6% on placebo. Fat mass fell 19.3%, and lean mass fell 9.7%. Because fat dropped faster, the share of their body that was lean mass actually rose, by 3.0 percentage points.

One detail matters for lifters. DXA "lean mass" isn't the same as muscle. It also includes water and organs. So a lean mass number tells you something about muscle, but it's not a direct muscle measurement.

Do GLP-1s make you lose muscle?

Some lean mass loss is common with any big weight loss, and how much varies a lot between studies.

A 2024 review by Neeland, Linge and Birkenfeld measures it a different way, as a share of the weight lost. By that measure, lean mass made up about 45% of the weight lost in STEP 1, and about 26% at the highest tirzepatide dose in SURMOUNT-1. Some studies show much less. The review puts the spread down to things like the drug, the dose, how fast weight comes off, how it's measured, who was studied and what lifestyle program came with it.

Researchers are still debating what that lean loss means. A review in Circulation asks whether it's a normal, adaptive response to losing weight or a harmful one. So the honest answer is that the size and meaning of the lean loss are being debated, not that GLP-1s "destroy muscle."

For reference, the SURMOUNT-1 trial of tirzepatide saw average weight loss of 15.0% to 20.9% over 72 weeks, depending on dose.

Should I still lift weights on Ozempic, Wegovy or Mounjaro?

If your doctor is happy for you to train, yes. Lifting is the part of the picture you control.

Both endurance and resistance exercise help preserve muscle during weight loss, but resistance exercise also improves strength. Fatigue is also a listed side effect on the Wegovy label, and it can make training harder. If that's you, tell your doctor.

Can a GLP-1 replace diet and exercise?

No, and the approvals don't claim it can. Both FDA labels pair the medicine with diet and activity. In the Zepbound trials described on its label, patients also got lifestyle counselling, including a deficit of about 500 kcal a day and a recommended minimum of 150 minutes of physical activity a week.

Do you gain the weight back when you stop?

In the STEP 1 extension, people who stopped semaglutide and the trial's lifestyle program regained about two-thirds of the weight they'd lost within a year.

That's another reason the habits you build around the medicine matter, including training.

How lifters can tell if they're keeping strength

The scale can't tell you whether you're holding on to muscle. Your training log can help. If your weight is dropping and your top sets are holding steady or going up, that's a useful sign. If your top sets keep sliding, that's worth raising with your doctor or coach.

We cover exactly how to set that up in how to track your training on a GLP-1.

Frequently asked questions

Do GLP-1s make you lose muscle?

Trials show some lean mass loss alongside fat loss, and how much varies between studies. In the STEP 1 substudy, fat mass fell 19.3% and lean mass fell 9.7%. Resistance training helps preserve strength.

Should I still lift weights on Ozempic, Wegovy or Mounjaro?

If your doctor agrees, yes. Resistance exercise helps preserve muscle during weight loss and also improves strength.

Is the weight you lose on a GLP-1 fat or muscle?

More fat than lean mass, though the split varies a lot between trials. DXA lean mass also includes water and organs, so it isn't a pure muscle measure.

Do you gain the weight back when you stop?

In the STEP 1 extension, people regained about two-thirds of the weight they'd lost within a year of stopping the medicine and the trial's lifestyle program.

Can a GLP-1 replace diet and exercise?

No. The FDA approvals are for use alongside a reduced-calorie diet and more physical activity.

Keep an eye on your strength

The scale can't tell you whether you're keeping your strength, but your top sets can. Twaka is an iPhone training tracker where you log sessions in plain English, and it keeps the history of each lift. It's on the App Store. Download Twaka on the App Store.

Sources

• U.S. FDA. Wegovy (semaglutide) prescribing information. DailyMed
• U.S. FDA. Zepbound (tirzepatide) prescribing information. FDA label
• Wilding et al. Impact of semaglutide on body composition in adults with overweight or obesity: exploratory analysis of the STEP 1 study. J Endocr Soc, 2021. PMC
• Neeland, Linge and Birkenfeld. Changes in lean body mass with GLP-1-based therapies and mitigation strategies. Diabetes Obes Metab, 2024. Wiley
• Neeland, Linge and Birkenfeld. Muscle mass and GLP-1 receptor agonists: adaptive or maladaptive response to weight loss? Circulation, 2024. AHA Journals
• Wilding et al. Weight regain and cardiometabolic effects after withdrawal of semaglutide: the STEP 1 trial extension. Diabetes Obes Metab, 2022. Wiley
• Jastreboff et al. Tirzepatide once weekly for the treatment of obesity (SURMOUNT-1). N Engl J Med, 2022. NEJM
• Therapeutic Goods Administration. Medicines containing GLP-1 and dual GIP/GLP-1 receptor agonists. TGA
• Therapeutic Goods Administration. Changes to the regulation of compounding GLP-1 RA products. TGA
• Therapeutic Goods Administration. Imported unregistered GLP-1 weight-loss products, 29 September 2025. TGA

This article is general information, not medical advice. It doesn't cover dosing or whether a medicine is right for you. Talk to your doctor before starting, stopping or changing any medication.