GLP-1 Trade-offs
Every lever moves more than one thing
GLP-1s are not a free lunch. The mechanisms that cause the weight loss also drive the downsides. Knowing them before you start lets you plan around them — most are manageable, some are hard limits.
Muscle loss is real
In STEP 1, about 40% of the total weight lost on semaglutide was lean mass. This is roughly on par with diet-only weight loss — not worse — but still meaningful. Prioritising protein (1.6–2.2 g/kg) and resistance training while on a GLP-1 preserves the lean tissue you want to keep.
Bone mineral density concerns
Whenever you lose significant weight fast, BMD can drop. GLP-1 trials show small but measurable reductions in hip and spine BMD at year 1. The long-term fracture-risk implications aren't yet clear — but resistance training + adequate vitamin D + calcium help offset the loss.
True or False
If you stop a GLP-1, the weight stays off.
This step is interactive — open the Thier app to try it.
Side effects you should plan for
Nausea (20–40%), vomiting (~10%), constipation, early satiety. These cluster during the first 4–8 weeks and dose-titration period. Rarer but serious: pancreatitis, gallbladder disease, thyroid C-cell concerns (boxed warning). Extremely rare: non-arteritic ischaemic optic neuropathy (NAION) — a 2024 observational finding still being evaluated.
Key Takeaway
GLP-1s work. They also take lean mass, reduce BMD, produce GI symptoms, and usually require long-term use. The best users pair them with resistance training, high protein, and a plan for what happens at year 2.