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What Causes What
MECHANISM− DECREASES

GLP-1 receptor agonist → Muscle strength

Higher GLP-1 receptor agonist decreases Muscle strength.

In 160 adults with obesity who sat for a DXA scan in SURMOUNT-1, weekly tirzepatide cut lean mass by 10.9 percent versus 2.6 percent on placebo (Look 2025). About a quarter of the lost weight was lean on both arms. Fat mass fell more.

Randomized trial · Moderate · N=160

Supported by an experiment or a tightly identified design. Read the caveats.

Mechanism

The pen cuts appetite. People eat less. Fat falls. Some lean tissue falls with it, as it does on a diet. That is not a stronger contraction and not a gym session. Look, Dunn, Kushner and colleagues (2025) scanned 160 of the 2,539 SURMOUNT-1 participants at baseline and week 72. Body weight, fat mass, and lean mass fell more on tirzepatide than on placebo: -21.3, -33.9, and -10.9 percent versus -5.3, -8.2, and -2.6 percent. Of the weight that was lost, about 75 percent was fat and 25 percent was lean on both arms. full_text. McCrimmon, Catarig, Frias and colleagues (2021) scanned 178 people with type 2 diabetes in SUSTAIN 8. Weekly semaglutide 1.0 mg and daily canagliflozin 300 mg both trimmed fat and lean mass. Fat fell 3.4 kg versus 2.6 kg. Lean fell 2.3 kg versus 1.5 kg. There was no placebo arm. full_text.

Caveats

Someone was assigned a pen, so the stamp is an RCT stamp. The living page also covers a one-rep max. These scans are lean mass, not a lift. Lean mass fell because weight fell. The share that was lean matched placebo. Water and glycogen can move a DXA reading without a weaker muscle. SURMOUNT-1 is obesity without diabetes. SUSTAIN 8 is type 2 diabetes versus an SGLT2 pill, not versus placebo. Did not hang the parent weight-loss papers (SURMOUNT-1, SURMOUNT-2, STEP 1) or the diabetes-prevention extension: those count kilograms, not lean mass. Did not hang the apitegromab-plus-tirzepatide stack. This page is a journal entry. It is not medical advice and not a reason to start or stop a drug.

Effect

percent_change = -10.9. SURMOUNT-1 DXA substudy N=160. Lean mass -10.9% tirzepatide vs -2.6% placebo. Fat mass -33.9% vs -8.2%. About 25% of lost weight was lean on both arms.

Nodes

Lifestyle & environmentGLP-1 receptor agonistBiology & endocrinologyMuscle strength

Named confounders

Cite this page

What Causes What. “GLP-1 receptor agonist → Muscle strength.” https://whatcauseswhat.org/edges/e-glp1-strength (atlas updated 2026-09-02).

https://whatcauseswhat.org/edges/e-glp1-strength

Papers