Tirzepatide

What it is

Tirzepatide is the dual-action drug from Eli Lilly that activates both GLP-1 and GIP receptors. It is approved as Mounjaro for type 2 diabetes (2022) and Zepbound for obesity (2023).

In trials it produces ~22% body-weight loss at 72 weeks at the top dose — the most for any approved obesity medication.

History

Disclosed publicly by Lilly in 2018, Phase III SURPASS (diabetes) trials 2021, SURMOUNT (obesity) trials 2022. Approved by FDA for diabetes 2022, for obesity 2023.

How it works

GLP-1 receptor activation reduces appetite and slows stomach emptying. GIP receptor activation has a less-understood role but appears to improve insulin sensitivity and may reduce the nausea associated with GLP-1 alone.

Dosage

• Starting dose: 2.5 mg once weekly for 4 weeks.
• Titration: 5 mg → 7.5 mg → 10 mg → 12.5 mg → 15 mg, every 4 weeks if tolerated.
• Maximum: 15 mg weekly. Most people get good results at 5–10 mg and never go higher.
• Maintenance after weight loss: lowest dose that holds the result, often 2.5–5 mg.

How it is taken

• Subcutaneous injection — abdomen, thigh, or back of upper arm.
• Rotate sites week to week to reduce lipohypertrophy (lumpy fat under skin).

How to reconstitute

• A 10 mg vial with 2 ml of BAC water gives 5 mg/ml. A 2.5 mg starter dose is 50 units.
• For very small starting doses, use more water (e.g. 4 ml) for finer measurement.

How it should arrive

Sealed glass vial, white powder or thin puck, intact cap. Ship cold or with a cold pack.

How it should look once reconstituted

Clear and colourless to slightly straw-tinted, no cloudiness or particles.

What to expect, and when

• Appetite suppression: within 24–48 hours of first dose.
• 12 weeks: typical loss is 5–10% of starting weight.
• 40 weeks: 15–20% loss in trials.
• 72 weeks: ~22% at top dose, plateau-ing.

Side effects

• Nausea, especially during dose increases.
• Constipation/diarrhoea, indigestion.
• Sulphur burps.
• Fatigue in the first 2–4 weeks.
• Reduced appetite is the point, but some find it crosses into not wanting to eat at all, which is a problem for protein and micronutrient intake.

Risks

• Pancreatitis — rare but documented.
• Gallstones — risk rises with rapid weight loss.
• Thyroid C-cell tumours seen in rodents; relevance to humans unclear.
• Muscle loss without adequate protein and resistance training.

Potential gains

• ~22% body weight loss at top dose over 72 weeks in trials.
• Significant blood glucose improvements; many type 2 diabetics achieve normal HbA1c.
• Reductions in blood pressure, lipids, liver fat.
• Reduced cardiovascular event risk (SURPASS-CVOT data).

Other useful information

The most rigorously studied GLP-1-class drug for weight loss. If you want strong evidence behind what you are taking, tirzepatide is the safest bet in this category.