Drug facts

How long does semaglutide take to work?

By David Chen·Editor·Reviewed September 2026

What the trial saw, and when³

STEP 1 followed 1,961 adults without diabetes for 68 weeks. Its report says weight loss on semaglutide “was observed from the first postrandomization assessment (week 4) onward, reaching a nadir at week 60.” By week 68 the average was 14.9%, against 2.4% on placebo.

The trial does not give a number for week 4 itself, only that the loss had begun. The nearest stated early figure comes from a different trial: in STEP 4’s 20-week run-in, people who reached 2.4 mg had lost 10.6% on average by week 20 — a group that excludes anyone who stopped along the way.⁴ Every point the trials publish, from week 4 to four years, is on semaglutide results by month.

The label’s first 16 weeks¹

That is the schedule for every Wegovy indication. For weight reduction in adults the maintenance dose is 1.7 mg or 2.4 mg, with 2.4 mg recommended, and a further step to 7.2 mg is allowed after at least four weeks on 2.4 mg. STEP 1 used the same ladder, reaching 2.4 mg by week 16. The whole schedule, with what each step costs, is on the dosage chart.

The calendar can stretch. The label says that if a dose is not tolerated during escalation, delaying the next step by four weeks can be considered — and that after two or more missed doses in a row, escalation restarts at a lower dose (missed doses). Either pushes week 17 later.

What the starting doses are for¹

The label gives one reason for the ladder: follow it “to reduce the risk of gastrointestinal adverse reactions.” The low doses are for starting treatment and climbing, not for staying on — Table 1 names 0.25 mg the “Starting Dosage” and 0.5 mg and 1 mg “Dosage Escalation,” and neither appears among the label’s maintenance doses. 1.7 mg is the exception: it is the last escalation step and also an approved maintenance dose.

None of that says the starting doses do nothing. STEP 1 recorded weight loss at week 4, on 0.25 mg. But the maintenance dose does not begin until week 17, which is why does compounded semaglutide work? lists “it is still early” first among the reasons it can seem not to.

Ozempic: the same start, a different finish²

Ozempic is semaglutide approved for type 2 diabetes, and its label opens the same way under a heading of “Recommended Initiation Dosage”: 0.25 mg once weekly for 4 weeks, then 0.5 mg. Its pen table marks 0.25 mg for “Initiation” and 0.5 mg, 1 mg and 2 mg for “Maintenance.” From there it climbs only if blood sugar needs it, at least four weeks at a time, to a maximum of 2 mg.

So “how long does Ozempic take to work” is really a question about blood sugar, measured in its trials over months — SUSTAIN 7, for example, reported at 40 weeks (the trial). How the two labels differ is on Ozempic vs Wegovy.

Appetite and the scale¹

The Wegovy label puts the mechanism plainly: “Semaglutide decreases calorie intake. The effects are likely mediated by affecting appetite.” After an injection, the concentration in the blood peaks one to three days later, and the drug’s half-life is about a week. How semaglutide works covers the receptor.

In a part of STEP 5, an eating questionnaire given at weeks 0, 20, 52 and 104 found hunger and fullness improved against placebo at week 20, and craving control improved at all three later visits.⁵ Week 20 is simply the first time it was asked, so the trial says nothing about the first weeks.

Side effects arrive first¹

In the Wegovy trials, gastrointestinal reactions were reported by 73% of people on 2.4 mg against 47% on placebo, and the label says they were “most frequently reported during dosage escalation.” The weeks when side effects are most often reported are the weeks before the maintenance dose. Every reaction with its placebo rate is on semaglutide side effects.

What this page is not

This reports what the labels and trials say about timing. When to step up, stay or stop is a prescriber’s decision, and nothing here is a suggestion to change a dose. See the medical disclaimer. If price is what sets the pace, the price index lists what each dose costs.