Tirzepatide
Tirzepatide is a long-acting injected medicine that acts on the receptors for two gut hormones, GIP and GLP-1. It is approved for type 2 diabetes, for weight management in people with obesity, and in the US for obstructive sleep apnoea in adults with obesity.
Reference information, not medical advice. Enhanced Training Studio doesn't sell, supply or recommend any substance. Doses are left out on purpose: only a prescriber can set one. How this library is written.
What it is
Tirzepatide is a man-made peptide made by Eli Lilly. It is sold as Mounjaro (for type 2 diabetes, and in the UK and EU also for weight management) and, in the US, as Zepbound (for weight management and sleep apnoea). It is given by injection under the skin. It is a prescription-only medicine and should only be used under medical supervision.
How it works
Tirzepatide activates the receptors for two gut hormones: glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) [1]. These hormones help control blood glucose after meals, and tirzepatide also acts on appetite centres in the brain to reduce food intake [1].
A fatty acid chain attached to the molecule lets it bind to the blood protein albumin, which slows its removal [1]. Its half-life is about five days, and peak blood levels are reached between 8 and 72 hours after injection [1].
Approved medical uses
- Type 2 diabetes: to improve blood glucose control alongside diet and exercise in adults and children aged 10 and over (Mounjaro) [2, 3].
- Cardiovascular risk reduction: to lower the risk of major cardiovascular events in adults with type 2 diabetes at high risk of these events (Mounjaro, US) [2].
- Weight management: in adults with obesity, or overweight with weight-related conditions, alongside diet and exercise (Zepbound in the US; Mounjaro in the UK and EU) [1, 3, 7]. In England, NICE recommends it for some adults with obesity within the NHS [8].
- Obstructive sleep apnoea: moderate to severe sleep apnoea in adults with obesity (Zepbound, US) [1, 5].
What the research shows
- In 72-week trials involving more than 2,500 adults with obesity or overweight, people on tirzepatide lost at least 15% of body weight on average, compared with about 3% on placebo [4]. At the highest dose studied, average loss was about 21% [1].
- Over 85% of participants on tirzepatide lost at least 5% of their weight [4].
- In trials of more than 6,000 adults with type 2 diabetes, tirzepatide lowered HbA1c (a measure of long-term blood glucose) more than placebo and the comparison treatments [4].
- In two 52-week trials of 469 adults with obesity and sleep apnoea, tirzepatide reduced the number of breathing pauses per hour of sleep compared with placebo. The FDA noted that this improvement was linked to weight loss [5].
Known risks and side effects
- Common: nausea, diarrhoea, vomiting, constipation, stomach pain, indigestion and injection site reactions [1]. In the main weight trials, between about 5% and 7% of people stopped treatment because of side effects, depending on dose [1].
- Thyroid tumours: tirzepatide caused thyroid C-cell tumours in rats. The human risk is unknown, but it must not be used by people with a personal or family history of medullary thyroid cancer or MEN 2 [1].
- Pancreatitis: acute pancreatitis, including rare severe and fatal cases, has been reported with GLP-1 and GIP/GLP-1 medicines. The MHRA strengthened this warning in 2026 [6].
- Other serious risks: gallbladder disease, kidney injury from dehydration, severe stomach and bowel reactions, allergic reactions, low blood sugar when used with insulin or sulfonylureas, and worsening diabetic eye disease [1]. Doctors should be told about it before surgery, because of a risk of breathing in stomach contents under anaesthesia [1, 7].
- Contraception and pregnancy: tirzepatide can reduce how well the contraceptive pill works, particularly after starting and after each dose increase, so UK guidance advises adding a barrier method during these periods [1, 7]. It should not be used in pregnancy, and UK guidance advises stopping it at least one month before trying to conceive [7].
- Unlicensed products: the FDA says compounded tirzepatide is not reviewed for safety, effectiveness or quality, and it has received hundreds of adverse event reports linked to it, as well as reports of fraudulent products [9]. The MHRA has seized illegally made tirzepatide pens and warns that such products may contain unknown or toxic substances [10].
Blood tests commonly monitored
- Blood glucose: before and during treatment in people with diabetes, especially when combined with insulin or sulfonylureas [1, 2].
- HbA1c: the main measure of glucose control in people with type 2 diabetes [2, 4].
- Kidney function: in people with vomiting, diarrhoea or dehydration [1].
- Calcitonin: the label states that routine calcitonin testing is of uncertain value for early detection of thyroid cancer [1].
- Lipase and amylase: rises were seen in trials; the label does not recommend routine testing without symptoms [1].
If you and your doctor are monitoring treatment, Enhanced Training Studio keeps a private log on your phone: what you take and when, your blood test results over time, and how you feel. How tracking works.
Sources
- US Food and Drug Administration / Eli Lilly. Zepbound (tirzepatide) injection: prescribing information. DailyMed, US National Library of Medicine, revised 2026. DailyMed: Zepbound
- US Food and Drug Administration / Eli Lilly. Mounjaro (tirzepatide) injection: prescribing information. DailyMed, US National Library of Medicine, revised 2026. DailyMed: Mounjaro
- European Medicines Agency. Mounjaro (tirzepatide): EPAR. EMA, updated 2026. EMA: Mounjaro
- European Medicines Agency. Mounjaro (tirzepatide): an overview of Mounjaro and why it is authorised in the EU. EMA, 2026. EMA: Mounjaro medicine overview
- US Food and Drug Administration. FDA approves first medication for obstructive sleep apnea. FDA, 2024. FDA press announcement
- Medicines and Healthcare products Regulatory Agency. GLP-1 and dual GIP/GLP-1 receptor agonists: strengthened warnings on the risk of acute pancreatitis. Drug Safety Update, 2026. MHRA Drug Safety Update
- Medicines and Healthcare products Regulatory Agency. GLP-1 medicines for weight loss and diabetes: what you need to know. GOV.UK, updated 2026. GOV.UK: GLP-1 medicines
- National Institute for Health and Care Excellence. Tirzepatide for managing overweight and obesity (TA1026). NICE, 2025. NICE TA1026
- US Food and Drug Administration. FDA's concerns with unapproved GLP-1 drugs used for weight loss. FDA, updated 2026. FDA: unapproved GLP-1 drugs
- Medicines and Healthcare products Regulatory Agency. MHRA smashes major illicit weight loss medicine production facility in record seizure. GOV.UK, 2025. MHRA: illicit facility seizure
Related
Last reviewed 7 October 2026. General information, not medical advice. Found a mistake? Email [email protected].