Semaglutide half life chart: what the numbers mean for your weekly dose

What the half life actually tells you, and what it does not

A drug's half life is the time it takes for the concentration in your bloodstream to fall by half. For semaglutide, that figure is consistently reported as approximately seven days across the clinical trials submitted to regulators, and you can read more about how the semaglutide half life is calculated and what it means in practice in our dedicated pharmacokinetics guide. You can also find the pharmacokinetic summary in the NHS semaglutide medicines page, which draws on the Summary of Product Characteristics approved by UK authorities.

The practical implication is straightforward: inject on a Monday, and by the following Monday roughly 50% of that dose is still circulating when you take the next one. This overlap is intentional. It means drug levels never crash to zero between injections, which produces a steadier appetite-suppressing effect than a shorter-acting medicine would.

What the half life chart does not tell you is how much weight you will lose, or how your body will respond, those questions depend on your biology, your dose, and the lifestyle changes you make alongside treatment. The pharmacokinetics set the schedule; the clinical response is individual.

It is worth noting that a seven-day half life is a population average. Factors such as body size and kidney function can shift the figure slightly for any individual, which is one reason a prescriber reviews your full health picture before deciding on a starting dose.

From first injection to steady state: reading the semaglutide half life chart across weeks

If you plot semaglutide blood levels across the first month or so of treatment, the pattern on the chart looks like a gradually rising staircase rather than a flat line. The first injection peaks one to three days later, then dips, but before it reaches baseline, the second dose arrives and pushes levels a little higher. This continues until, around week four or five, the accumulation plateaus into what pharmacologists call steady state.

Steady state is clinically significant because the titration schedule mirrors it. Treatment begins at 2.5 mg weekly (for semaglutide injection) to let the body adjust, with dose increases typically following each four-week block. By the time a dose increase is considered, the previous dose has had long enough at steady state for the prescriber to assess tolerability, that is not a coincidence in how the schedule was designed.

If you are curious how this compares with the longer-acting oral version, our guide to the half life of the Wegovy 25 mg tablet covers the different pharmacokinetic profile of oral semaglutide, where absorption dynamics change the picture considerably.

Many people find this build-up phase the most uncertain part of treatment. Levels are still rising, side effects are most likely in these early weeks, and the full appetite effect has not yet kicked in. That is entirely expected and does not mean the medicine is not working.

What happens when a dose is missed or treatment stops

Because the half life is roughly seven days, missing a single weekly injection does not produce an abrupt drop-off. Levels fall by around half over the first week after a missed dose, then by half again over the following week, and so on. This is a gentler pharmacological exit than you would see with a short-acting medicine, which explains why the clinical guidance (set out in the prescribing information and summarised on the NHS England weight management injections page) allows a degree of flexibility around a single missed dose before recommending a restart at a lower dose.

Full clearance after the last dose takes approximately five half lives, in practical terms, around five weeks. This is relevant in several contexts: switching between medicines, planning surgery, and contraception decisions for women of childbearing age. The MHRA advises using contraception during treatment and for a wash-out period before trying to conceive, so understanding that semaglutide remains pharmacologically active for several weeks after the final injection is not just theoretical.

For a broader look at how these timelines interact with specific doses, the Wegovy peak and half life page explores the peak-to-trough curve at different maintenance doses, including the newer 7.2 mg strength. Stopping decisions should always be discussed with your prescriber rather than made unilaterally; the pharmacokinetics are one input, not the whole picture.

Semaglutide versus tirzepatide: does the half life chart change the decision?

Tirzepatide (Mounjaro) also has a pharmacokinetic half life of approximately five days, slightly shorter than semaglutide's seven. Both medicines are dosed once weekly, and both reach steady state over the first few weeks of treatment. For most people, the difference in half life is not what drives the choice between them.

What does matter clinically is the mechanism: semaglutide acts on GLP-1 receptors alone, while tirzepatide is the UK's only dual GIP and GLP-1 receptor agonist. The NICE appraisal of tirzepatide (TA1026) noted that head-to-head trial data favoured tirzepatide for average weight reduction, though both medicines produce meaningful results for many people. Which one is appropriate for you is a clinical decision, not a pharmacokinetics one.

If cost is part of your thinking, our Wegovy cost page sets out the private pricing landscape honestly, including what a legitimate prescription-based service includes beyond the medicine itself. And if you want a fuller overview of how semaglutide is used in weight management, including the other names Wegovy is known by and how the branding relates to the underlying medicine, the semaglutide guide covers the licensed indications, trial evidence and what to expect at different stages of treatment.

When you are ready to explore whether semaglutide-based treatment is clinically suitable for you, our prescribers review every consultation the same day. Speak to our prescribers through a free consultation at nume, there is no commitment, and the clinical review happens before any treatment decision is made.