GLP-1 and metabolic medicine

Zepbound

Also called: tirzepatide weight loss, Zepbound pen

Zepbound is the US brand name Eli Lilly uses for tirzepatide when it is licensed for weight loss. It is the same drug as Mounjaro, just badged for a different licensed use. It activates both GLP-1 and GIP receptors and produces the largest average weight loss of any approved GLP-1 medication in trials.

Zepbound vs Mounjaro

Both are tirzepatide. Same molecule, same pen design, same dose ladder. The only differences are the brand name and the licensed indication. Mounjaro is licensed for type 2 diabetes (and, in the UK, for weight management as well). Zepbound is the US brand specifically for weight management and is not used outside the United States.

How it works

Tirzepatide activates GLP-1 and GIP receptors at the same time. Both are gut hormones released after meals. Activating both slows gastric emptying, raises insulin sensitivity, and signals fullness to the brain. The combined effect lowers appetite and total calorie intake without conscious effort.

What the trials showed

  • SURMOUNT-1: about 22.5 percent average weight loss at 72 weeks on the 15 mg dose, against 2.4 percent on placebo.
  • SURMOUNT-5 (head-to-head with semaglutide): 20.2 percent on tirzepatide vs 13.7 percent on semaglutide at 72 weeks.
  • Across SURMOUNT-1 doses, the share losing at least 5% of body weight was 85% on 5mg, 89% on 10mg, and 91% on 15mg (Jastreboff 2022). Around 36 percent on 15mg lost at least 25 percent.

Side effects

  • Nausea, especially after each dose increase. Usually settles within 1 to 2 weeks.
  • Constipation. SURMOUNT-1 reported around 12 to 17 percent across the dose range.
  • Diarrhoea, in a smaller number of users, often early in treatment.
  • Reflux, burping, fatigue.
  • Rare but serious: pancreatitis, gallstones, severe gastroparesis.

If you are in the UK

Zepbound is a US-only brand. The same drug is sold in the UK as Mounjaro for both diabetes and weight management. NICE TA1026 covers tirzepatide for adults with BMI 35 or over plus a weight-related condition. Per NICE: 'Tirzepatide can be used in primary care or specialist weight management services', NHS England is rolling it out in phases, starting in specialist services, but the NICE guidance does not restrict it to Tier 3.

Common questions

Is Zepbound the same drug as Mounjaro?
Yes, both are tirzepatide. Same molecule, same pen, same dose ladder. Different brand name and different licensed use. Zepbound is the US weight-loss brand. Mounjaro is the diabetes brand globally and the weight-management brand in the UK.
Is Zepbound stronger than Wegovy?
In direct comparison (SURMOUNT-5), tirzepatide produced more weight loss than semaglutide at the same time point: 20.2 percent vs 13.7 percent at 72 weeks. The trade-off is that tirzepatide is newer with less long-term safety data.
Can I get Zepbound in the UK?
Not under that brand name. The UK has tirzepatide under the Mounjaro brand for both diabetes and weight management. The drug is the same.
Why does Zepbound work better than diet alone?
It changes the underlying signalling. Diets fail because hunger and reward signals from the gut and brain push back hard against calorie restriction. Tirzepatide quiets those signals, so the calorie deficit feels sustainable instead of like a willpower fight.

Sources