Is Mounjaro just 'better' than Wegovy?

On weight loss, yes, SURMOUNT-5 was conclusive. On safety, similar profiles but Wegovy has more years of post-launch data. On cardiovascular outcomes, Wegovy has more evidence. So Mounjaro wins for weight loss specifically; Wegovy wins for established record. The right choice depends on what you're optimising for.

Should I switch from Wegovy to Mounjaro?

If you're losing weight steadily and tolerating Wegovy, probably no reason to switch. If you've been on the maximum 2.4 mg for 6+ months and weight loss has stalled, switching is reasonable under prescriber supervision. Don't self-switch; the dose ladders are different.

Are the side effects worse on Mounjaro?

Largely similar at equivalent therapeutic levels. Mounjaro has slightly more diarrhoea and slightly less constipation than Wegovy, but the differences are modest. The dose ladder pace matters more than the drug, going up too fast on either causes more nausea than necessary.

No, never. Combining two GLP-1 agonists is not safe and provides no additional benefit. If switching between the two, there's a brief washout period (typically 1-2 weeks) before starting the new drug at its starter dose.

Mounjaro vs Wegovy

3 min readUpdated 2026-04-26By Dr Chad Okay

Different drugs. Mounjaro is tirzepatide (a dual GLP-1 + GIP agonist). Wegovy is semaglutide (GLP-1 only). In the SURMOUNT-5 head-to-head trial, tirzepatide produced more weight loss (20.2% vs 13.7% at 72 weeks). Side effect profiles are similar. Wegovy has more years of post-launch safety data. Both are weekly injections. UK access is via specialist Tier 3 services for both, or private prescription.

Mounjaro and Wegovy are the two most-prescribed GLP-1 drugs for weight loss in the UK right now. They look similar, work similarly, but they're different molecules with different efficacy and slightly different safety histories. Here's the actual head-to-head.

What's different

	Mounjaro	Wegovy
Active drug	Tirzepatide	Semaglutide
Drug class	Dual GLP-1 + GIP receptor agonist	GLP-1 receptor agonist
Manufacturer	Eli Lilly	Novo Nordisk
Maximum dose	15 mg weekly	2.4 mg weekly
Average weight loss at 72 weeks	20.2% (SURMOUNT-5 head-to-head)	13.7% (SURMOUNT-5 head-to-head)
UK NHS access	NICE TA1026, specialist services	NICE TA875, specialist services
Years on market for weight loss	From 2024	From 2021

Why tirzepatide produces more weight loss

Tirzepatide activates two gut hormone receptors instead of one. GLP-1 is the same target as semaglutide. GIP is an additional gut hormone that influences insulin release, fat storage, and central appetite signalling. Activating both at once produces stronger effects on appetite suppression and metabolic improvement than GLP-1 alone. The trade-off was that tirzepatide is newer with less long-term safety data, but the data accumulating is reassuring so far.

SURMOUNT-5: the head-to-head trial

Published 2025. 751 adults with obesity, no diabetes.
72 weeks of treatment.
Average weight loss: tirzepatide 20.2%, semaglutide 13.7%.
Tirzepatide users were more than twice as likely to lose 25% or more of body weight (about 32% vs 16%).
Side effect rates were broadly similar: nausea around 44% on both, GI issues most common in early weeks.
First randomised comparison; clear winner on weight loss.

What's the same

Schedule: both weekly injections.
Pen design: very similar.
Storage: refrigerated, room temperature once in use.
Dose ladder pace: both titrate up over 16-20 weeks to limit side effects.
Side effect profile: nausea, constipation, reflux, fatigue. Mounjaro slightly more diarrhoea, Wegovy slightly more constipation.
Rare serious risks: pancreatitis, gallstones, severe gastroparesis on both. Persistent severe abdominal pain warrants stopping.

Which to ask for

Maximum weight loss is the primary goal: lean Mounjaro on the SURMOUNT-5 evidence.
Longer track record matters more to you: Wegovy has 3+ extra years of post-launch use.
You've already responded well to Wegovy and tolerate it: probably no reason to switch.
You've not responded to Wegovy after 6+ months at 2.4 mg: switching to Mounjaro is reasonable.
You can't tolerate the GI effects of Wegovy: Mounjaro often (but not always) causes similar issues.
Cardiovascular outcomes evidence matters most (you have prior heart disease): Wegovy currently has more CV outcomes data; tirzepatide trials are still maturing.

Cost and access in the UK

NHS: both available via specialist Tier 3 weight-management services for adults with BMI ≥35 plus a weight-related condition. Capacity is limited.
Private clinics: both around £150-300 per month depending on dose. Mounjaro often slightly cheaper at the lower-equivalent doses.
Pharmacy supply has been intermittent for both during the global demand surge. Mounjaro supply has been more stable since mid-2025.

Common questions

Is Mounjaro just 'better' than Wegovy?: On weight loss, yes, SURMOUNT-5 was conclusive. On safety, similar profiles but Wegovy has more years of post-launch data. On cardiovascular outcomes, Wegovy has more evidence. So Mounjaro wins for weight loss specifically; Wegovy wins for established record. The right choice depends on what you're optimising for.
Should I switch from Wegovy to Mounjaro?: If you're losing weight steadily and tolerating Wegovy, probably no reason to switch. If you've been on the maximum 2.4 mg for 6+ months and weight loss has stalled, switching is reasonable under prescriber supervision. Don't self-switch; the dose ladders are different.
Are the side effects worse on Mounjaro?: Largely similar at equivalent therapeutic levels. Mounjaro has slightly more diarrhoea and slightly less constipation than Wegovy, but the differences are modest. The dose ladder pace matters more than the drug, going up too fast on either causes more nausea than necessary.
Can I take both?: No, never. Combining two GLP-1 agonists is not safe and provides no additional benefit. If switching between the two, there's a brief washout period (typically 1-2 weeks) before starting the new drug at its starter dose.