Half-life

Half-life is a measure of how long a drug stays active in the body — specifically, the time it takes for the concentration of the drug in the blood to drop by half. Most GLP-1 medications have long half-lives (around a week), which is why they're typically dosed weekly rather than daily.

Related guides

Obesity phenotypes: why "hungry gut" vs "hungry brain" may change your GLP-1 results — Researchers now describe four "phenotypes" of obesity — hungry brain, hungry gut, emotional hunger, and slow burn — and early evidence suggests they help explain why the same GLP-1 produces dramatically different results in different people. One newly described "hungry gut" subtype lost nearly twice as much weight on tirzepatide. Here's what the phenotypes are, what the studies actually show, and what to know before paying for a phenotype test.

Does loose skin throw off your DXA, BIA, or Seca body-composition results? — Loose skin is fat-free tissue that body-composition scanners have no separate box for — so after large weight loss it can nudge your DXA "lean mass" up and your body-fat % down, and it complicates BIA and Seca readings too. Here's how each method (DXA, BIA/Seca, MRI) handles loose skin, how to rate them for a body carrying a lot of it, and how to read your results anyway.

What the ADA guidelines say about GLP-1 medications — and what changed for type 1 diabetes in 2026 — The American Diabetes Association's Standards of Care is the reference most US clinicians follow, and it now puts GLP-1 medications at the center of treating diabetes with obesity. Here's what the guideline actually recommends — GLP-1s as the preferred obesity medication in type 2 diabetes, realistic weight-loss targets, the "highest dose isn't always the goal" point on dosing — plus the headline 2026 change: for the first time, the ADA cautiously supports GLP-1 therapy for people with type 1 diabetes and obesity, with important safety guardrails.

GLP-1 super-responders (and non-responders): why weight loss varies so much — On the same drug at the same dose, one person loses 25% of their body weight and another loses almost nothing. Clinical trials suggest a third or more can reach 20%+ loss — but a large real-world analysis found only about 1 in 8 lost more than 15% in a year, while nearly half lost under 5%, much of it down to adherence and dosing. Here's what separates strong responders from weak ones — early response, drug choice, sex, diabetes, biology — and what to do if you're not one.

Reading your DXA results over time: tracking fat vs. lean mass on a GLP-1 — Your second DXA report is only useful if you can tell real change from measurement noise. Here's how to read the key numbers over time — fat mass, lean mass, body fat %, visceral fat, bone density — what a good GLP-1 trajectory looks like, why small changes may be noise, and how to shift the fat-to-lean loss ratio.

Loose skin after GLP-1 weight loss: what actually helps and what's hype — Loose or excess skin on the belly, arms, and thighs is a common worry after large GLP-1 weight loss. Here's what the evidence actually supports — gradual loss, muscle, nutrition, time — versus the creams and wraps that promise more than they deliver, and when surgery is the only real fix.