When switching from Wegovy to Mounjaro makes sense

• You've plateaued on Wegovy maintenance (2.4mg). If you've been on the full Wegovy dose for 3+ months and weight loss has stalled below your target, Mounjaro's dual mechanism often unlocks further progress.
• You're tolerating Wegovy well and want the higher headline weight loss. SURMOUNT-1 showed ~21% mean weight loss on Mounjaro 15mg vs STEP-1's ~15% on Wegovy 2.4mg.
• You have type 2 diabetes alongside obesity. Mounjaro's GIP activity gives slightly better glucose control on average than pure GLP-1 agonists.
• Wegovy stock issues are interrupting your supply. Mounjaro supply has generally been more reliable in 2026.

When switching is the wrong call

• You're tolerating Wegovy poorly. Mounjaro side effects tend to be slightly more pronounced because of the dual GLP-1/GIP mechanism. If Wegovy has been hard, Mounjaro probably will be too.
• You have established cardiovascular disease. Semaglutide has the SELECT trial (2023) showing reduced cardiovascular events. Tirzepatide doesn't have equivalent CVD outcomes data yet.
• You're nearing your target weight. The marginal benefit of switching at the maintenance phase is small. Stay on Wegovy if it's working.

The recommended washout period

Wegovy and Mounjaro share overlapping mechanisms (both hit the GLP-1 receptor). Taking them simultaneously would significantly increase side effects without proportional weight-loss benefit, and isn't licensed.

The safe approach: take your final Wegovy injection on your usual day, wait one full week (so your next Wegovy dose would have been due), then start Mounjaro 2.5mg the day after. This gives Wegovy's effective concentration time to fall while keeping appetite suppression continuous.

If you've been off Wegovy for longer (e.g. you stopped a few weeks ago), no washout is needed — start Mounjaro 2.5mg whenever's convenient.

What dose to start Mounjaro on

The standard answer is: start at 2.5mg — the same starting dose as a Mounjaro-naive patient. This is because:

• Mounjaro has the additional GIP receptor activity that your body hasn't been exposed to on Wegovy
• The 2.5mg starting dose is a tolerance-building dose, not a therapeutic dose
• Skipping to a higher starting dose dramatically increases side effects

Some clinicians will start at 5mg if a patient has been on Wegovy 2.4mg with no side effects for several months. This is off-label and not what we'd recommend as a default — but case-by-case, it's possible. The free consultation covers your specifics.

What to expect in the first 4 weeks of Mounjaro

The first 2–3 weeks are typically the hardest:

• Hunger may briefly return as Wegovy's effect wanes and Mounjaro's 2.5mg dose builds up. This is normal and temporary — don't panic-eat your way through it.
• Nausea is more likely in the first 2 weeks than it is restarting Wegovy, because of the GIP component your body hasn't encountered before.
• Bowel habits may change again — usually back to whatever they were when you first started Wegovy, then settle.
• Weight may plateau briefly before resuming the downward trajectory. Most patients restart losing weight by week 4–6.

By month 2 (when you escalate to Mounjaro 5mg), most patients are comfortable and seeing weight loss again.

Common pitfalls when switching

• Starting Mounjaro before the washout completes. Doubles up the GLP-1 effect for a week — significant side effects guaranteed.
• Starting at too high a dose. Skipping the 2.5mg starter is a common cause of intolerable nausea and people quitting the switch.
• Expecting the switch to fix lifestyle issues. If you've been compensating for Wegovy with high-calorie low-volume foods, Mounjaro won't override that.
• Not telling your GP. Particularly important if you're on medications that interact with GLP-1s (insulin, sulfonylureas) — needs careful management.

Switching back if Mounjaro doesn't suit you

Yes, this happens — about 1 in 10 patients switch to Mounjaro and find side effects intolerable. The reverse switch (Mounjaro back to Wegovy) follows the same protocol: take your last Mounjaro injection, wait one full week, restart Wegovy at 0.25mg. No shame in this, and we manage both directions at Preston Clinic.