What Is Semaglutide? Dosage, Half-Life & How to Track It

What semaglutide is and how it works

Semaglutide mimics GLP-1 (glucagon-like peptide-1), a hormone your gut releases after eating. Activating the GLP-1 receptor does several useful things at once: it prompts glucose-dependent insulin release, slows gastric emptying so you feel full longer, and quiets appetite signaling in the brain — the “food noise” people describe going quiet.

The result is reduced intake without white-knuckle willpower, which is why it is approved both for type 2 diabetes (as Ozempic) and chronic weight management (as Wegovy). Semaglutide also comes as a once-daily oral tablet (Rybelsus) — the same molecule, taken on an empty stomach with a small sip of water — though the once-weekly injection remains the more common route. Same molecule throughout; the brand differs by indication, dose, and route.

For comparison, tirzepatide adds a second receptor (GIP) to the same idea — that head-to-head is worth its own read, linked below.

Typical dosing & titration

Prescription semaglutide comes in a pre-filled pen; reconstitution math only applies to compounded or research vials of lyophilized powder. Either way the escalation ladder is the same, and gentle on purpose — each step is once weekly, same day each week, with or without food:

• Weeks 1–4: 0.25 mg
• Weeks 5–8: 0.5 mg
• Weeks 9–12: 1.0 mg
• Weeks 13–16: 1.7 mg
• Weeks 17+: 2.4 mg (maintenance)

If you reconstitute a vial yourself, concentration drives your units. A detail the calculator handles automatically: with a 5 mg vial in 2 mL, the 2.4 mg maintenance dose is 96 units — just under a full 1 mL syringe, which is why 2 mL is chosen over 3 mL for that vial size.

Half-life & what it means for frequency

Semaglutide’s half-life is roughly 7 days — unusually long for a peptide, achieved by binding to albumin in the blood so it isn’t cleared quickly. That single fact explains the whole once-weekly schedule and a couple of downstream behaviors.

Because a week is about one half-life, levels accumulate for the first several weeks before reaching steady state — so week 3 on a dose can feel different from week 1, and that is expected, not the drug “wearing off.” The long tail also means stopping isn’t instant: it takes weeks to clear, and appetite tends to return as it does. You can watch that accumulate-and-plateau shape in the blood-level simulator.

What to track & common side effects

The side effects are overwhelmingly gastrointestinal — nausea, constipation, reflux, occasionally vomiting — and they cluster right after each dose increase, then settle. Nausea affects up to roughly a quarter of users. They are the reason the titration is slow; escalating faster just trades weeks for more misery.

Two things worth actively tracking. Muscle: a meaningful share of the weight lost can be lean mass, so protein (about 1.6 g/kg/day) and resistance training matter. And the trend: weight, waist, and how each dose is tolerated tell you whether to hold a dose or step up — far more useful than any single scale reading.

Frequently asked questions