How Wegovy works in your body

Wegovy is a GLP-1 receptor agonist. GLP-1 (glucagon-like peptide-1) is a gut hormone released after meals that signals fullness to your brain and slows gastric emptying. Semaglutide is a synthetic, long-acting version of GLP-1 — one weekly injection sustains the appetite-suppression effect across all 7 days.

The practical experience: your appetite drops, you feel full sooner, food cravings become much quieter, and the gap between meals naturally lengthens. It's the same general experience as Mounjaro, but most patients describe the appetite suppression as slightly less pronounced than with tirzepatide. Wegovy works on one hormone pathway (GLP-1); Mounjaro works on two (GLP-1 and GIP).

Who's eligible under NICE guidance

NICE TA875 recommends semaglutide for adults with a BMI of 30 or above with at least one weight-related condition (type 2 diabetes, hypertension, sleep apnoea, dyslipidaemia, cardiovascular disease). The NICE eligibility is slightly tighter than Mounjaro's. Not licensed under 18 or in pregnancy. Same contraindications as Mounjaro for medullary thyroid cancer history. The free consultation at Preston Clinic checks eligibility against the SmPC.

The dose schedule, month by month

Wegovy comes in a pre-filled pen and is injected once weekly. The dose escalates over 16–20 weeks:

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

The escalation is slower than Mounjaro's, which means side effects tend to be milder week-to-week — but it also takes longer to reach the therapeutic dose. Most patients are on the maintenance 2.4mg dose by month 4–5.

What weight loss actually looks like — the real numbers

From STEP-1 (1,961 adults without diabetes):

• 2.4mg dose at 68 weeks: ~15% mean weight loss
• Placebo: ~2.4% mean weight loss

In practice: most patients see 2–4kg in the first 3 months (slower start than Mounjaro because of the gentler escalation), 6–10kg by month 6, and 10–15kg by 12 months. Some patients lose more, particularly when combined with sustained behaviour change.

Side effects — what to expect

The side effect profile is similar to Mounjaro but generally milder, because the dose escalation is slower:

• Nausea (about 20% in trials, vs 25% on Mounjaro)
• Diarrhoea or constipation — common
• Indigestion and burping — common
• Headache and fatigue in the first few weeks

Most side effects settle within 4–8 weeks of each dose increase. Gallbladder problems (~1–2%) and pancreatitis (rare) are the less-common-but-important ones — stop and seek medical attention for severe abdominal pain.

When Wegovy is the better choice than Mounjaro

Mounjaro has the higher headline weight loss number, but Wegovy is the better choice when:

• You can't tolerate the faster Mounjaro escalation — slower dose ramp = milder symptoms
• You're sensitive to side effects — generally milder on Wegovy
• You've already tried Mounjaro and didn't tolerate it — different molecule, sometimes better tolerated
• You have cardiovascular disease — semaglutide has a stronger cardiovascular outcomes evidence base (SELECT trial, 2023)
• Stock availability — Mounjaro has had supply constraints in 2024–25; Wegovy has been more reliably available

NHS vs private

The NHS prescribes Wegovy through Tier 3 weight management services for eligible patients. Waiting lists are 12–24 months in most areas. Private treatment removes the wait — at Preston Clinic, the free consultation, prescription, and monthly reviews are included. You pay only for the medication.

Honest comparison: Wegovy vs Mounjaro

If both are options for you, here's the realistic picture:

• Mounjaro: More weight loss on average (~21% vs ~15%). Faster onset of appetite suppression. More side effects in the first 8 weeks. Currently more expensive at maintenance doses.
• Wegovy: Slightly less weight loss but still substantial. Slower onset (because of slower dose escalation). Milder side effect profile. Stronger cardiovascular outcomes evidence. Often more reliably in stock.

Most of our patients start on Mounjaro because the numbers are better — but a meaningful minority do better on Wegovy. The free consultation covers which is right for your specifics.