When does Wegovy start working?
Wegovy starts reducing appetite within the first week, but it does not reach its full dose until week 17. The titration runs through five steps of four weeks each: 0.25, 0.5, 1.0, 1.7 and finally 2.4 mg. Measurable weight change usually appears at four to six weeks, and by three months most people have lost 6 to 7 per cent of body weight. The headline figure of 14.9 per cent from the STEP-1 trial took 68 weeks. Wegovy feels the slowest of the GLP-1 treatments to get going, and that is a feature of the schedule rather than a fault.
What happens in the first four weeks on Wegovy
Semaglutide reaches peak concentration one to three days after injection and has a half-life of about a week, which is why Wegovy is dosed weekly. The drug is doing something from the first injection.
What you notice in weeks one to four is appetite, not weight. People describe smaller portions feeling like enough, and the background hum of thinking about food quietening down. The 0.25 mg starting dose is deliberately below the therapeutic range; it exists to let your stomach adapt, not to produce a result.
If the scale has not moved by the end of week four, nothing has gone wrong. Almost nobody loses meaningful weight on 0.25 mg, and it was never designed to.
Why Wegovy takes 16 weeks to reach full dose
This is the single most important thing to understand before you start, and it is where most of the disappointment comes from.
Wegovy steps up every four weeks through five doses. You are on 2.4 mg, the dose STEP-1 was built around, from week 17 onward. Mounjaro reaches a therapeutic dose considerably faster, which is a large part of why its three-month numbers look better.
The schedule exists to limit nausea and vomiting. Moving faster does not produce faster weight loss; it produces side effects severe enough that people stop altogether, which is the worst outcome of all. If your prescriber holds you at a dose for longer than four weeks because you are struggling, that is good practice rather than delay.
The week-by-week picture
- Weeks 1 to 4, 0.25 mg. Appetite changes. Scale usually flat. Some nausea in the days after each injection.
- Weeks 5 to 8, 0.5 mg. First measurable weight change for most people, typically 1 to 3 kg.
- Weeks 9 to 12, 1.0 mg. Loss becomes steady. Around 5 per cent of body weight by week twelve is a normal result.
- Weeks 13 to 16, 1.7 mg. Appetite suppression noticeably stronger.
- Week 17 onward, 2.4 mg. Full dose. The steepest part of the curve runs from here to roughly month twelve.
Side effects, and when they arrive
Nausea is the commonest, and it follows a predictable pattern: it clusters in the two or three days after a dose increase, then fades as you settle at that dose. Constipation, reflux and fatigue are also common. Most of it is manageable and most of it improves.
Smaller meals, eating slowly, stopping before full, and avoiding heavy fatty food in the days after an injection all help more than people expect. Persistent vomiting, severe abdominal pain radiating to the back, or signs of dehydration are different, and warrant contacting your prescriber rather than waiting it out.
What the STEP-1 trial actually showed
STEP-1 studied semaglutide 2.4 mg in adults with obesity or overweight without diabetes. Average weight reduction was 14.9 per cent over 68 weeks, against 2.4 per cent on placebo. Roughly a third of participants lost 20 per cent or more.
Two caveats worth carrying. Every participant received structured lifestyle support alongside the injection, so the trial never tested the drug alone. And an average of 14.9 per cent conceals a wide spread, with a minority losing very little.
Getting Wegovy in Ireland
Wegovy is prescription-only and licensed specifically for weight management, which is a meaningful difference from Ozempic. Because the licensed indication is weight rather than diabetes, it generally sits outside the Long Term Illness Scheme, though the Drugs Payment Scheme still caps a household at €80 a month across all prescribed medicines.
Supply has been intermittent across Irish pharmacies since launch, and it has tended to be tighter outside the Dublin and Cork areas. If a pharmacy in Sligo, Kilkenny or Tralee tells you they have none, it is usually worth asking them to order it in rather than concluding the country is dry.
When does Wegovy start working: common questions
Appetite usually reduces within the first week of the first injection. Measurable weight change on the scale typically appears at four to six weeks, once you have moved up from the 0.25 mg starting dose.
The 0.25 mg dose is a starting dose intended to let your stomach adapt, not to produce weight loss. Almost nobody loses meaningful weight on it. The first measurable change usually comes at 0.5 mg or above.
Seventeen weeks. The schedule runs 0.25, 0.5, 1.0, 1.7 and 2.4 mg, four weeks at each step. Your prescriber may hold you at a dose for longer if side effects require it.
Roughly 6 to 7 per cent of starting body weight, which is about 6 to 7 kg for a 100 kg person. This is lower than the headline trial figure because at three months you have only just reached the full dose.
Wegovy reaches a higher dose of the same drug, so its total effect is greater, but its 16-week titration means it does not feel faster early on. Ozempic is licensed for type 2 diabetes and tops out at a lower semaglutide dose.
Nausea usually clusters in the two or three days after each dose increase and fades as you settle at that dose. For most people it becomes much less troublesome after the first two or three steps of the titration.