The short version
- GLP-1 medicines such as semaglutide and tirzepatide are prescription drugs. Only a licensed clinician can decide if they are right for you.
- In trials, part of the weight people lost was lean mass, not only fat.
- Expert nutrition groups emphasise enough protein and regular strength training during treatment.
This page is education only. We do not recommend, dose or compare medicines. Talk to your prescriber about anything here.
What the research shows
In the STEP 1 trial of semaglutide 2.4 mg, people lost substantially more weight than with placebo. A body-scan sub-study found that lean mass, which includes muscle, made up a meaningful share of the weight lost. This is also true with other ways of losing weight; the larger and faster the loss, the more it matters.
Habits to discuss with your clinician
- Protein at each meal, even when appetite is low. Use the protein calculator as a starting point for that conversation.
- Strength training 2–3 days a week (full-body plan).
- Fluids and fibre (fibre guide).
Safety
The FDA has warned people not to buy these medicines from unlicensed online sellers and about risks with unapproved or compounded versions. Report side effects to your clinician.
Common mistakes and fixes
- Skipping meals because appetite is low. Fix: Small protein-first meals; ask your clinician or a dietitian for a plan.
- Stopping strength training. Fix: Keep 2–3 sessions a week if your clinician agrees.
- Buying medicine from unlicensed websites. Fix: Use a licensed prescriber and pharmacy only.
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Questions people ask
Does Ozempic cause muscle loss?
Some of the weight lost on GLP-1 medicines is lean mass, as with other weight loss. Discuss protein and strength training with your clinician.
Can I buy GLP-1 medicines online without a prescription?
No. The FDA warns against unlicensed sellers.
Sources
- Wilding JPH et al. Once-weekly semaglutide in adults with overweight or obesity (STEP 1). N Engl J Med, 2021. Checked October 23, 2026.
- FDA. Medications containing semaglutide marketed for type 2 diabetes or weight loss. Checked October 23, 2026.
- NIH NIDDK. Prescription medications to treat overweight and obesity. Checked October 23, 2026.
Education only. Not medical advice. Confirm with your clinician.