Dual GIP/GLP-1 Receptor Agonist — Type 2 Diabetes / Obesity Pregnancy: Weight loss offers no benefit in pregnancy and may cause fetal harm; advise against weight loss in pregnancy and discontinue when pregnancy is recognised. Human data insufficient; animal studies showed fetal growth reductions and abnormalities. Pregnancy exposure registry exists.

Tirzepatide

Brand names: Mounjaro, Zepbound

Tirzepatide is a once-weekly injectable incretin therapy used in type 2 diabetes mellitus and in weight management, improving glycaemic control and promoting weight loss. It is administered by subcutaneous injection.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: Starting 2.5 mg once weekly for 4 weeks, then increase to 5 mg once weekly; maintenance 5 mg, 10 mg or 15 mg once weekly

Route: Subcutaneous injection (abdomen, thigh, or back of upper arm; rotate sites)

Frequency: Once weekly, any time of day, with or without meals

Max: 15 mg once weekly (maximum for all indications)

US label (ZEPBOUND, Eli Lilly) — no UK SPC posology in the bundle; verify against UK SPC. Escalate in 2.5 mg increments after at least 4 weeks on the current dose to reduce GI adverse reactions; the 2.5 mg dose is for initiation only and is not a maintenance dose. Consider treatment response and tolerability when selecting maintenance dose; if a maintenance dose is not tolerated, consider a lower one. Obstructive sleep apnoea: maintenance 10 mg or 15 mg once weekly. Missed dose: give within 4 days (96 hours), otherwise skip; at least 3 days (72 hours) between doses. Give with reduced-calorie diet and increased physical activity. Paediatric: safety and effectiveness not established.

Dose auto-extracted from US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

Personal or family history of medullary thyroid carcinoma (MTC), or Multiple Endocrine Neoplasia syndrome type 2 (MEN 2)
Known serious hypersensitivity to tirzepatide or any excipient (anaphylaxis and angioedema reported)

Side effects

Nausea
Diarrhoea
Vomiting
Constipation; abdominal pain; dyspepsia
Injection site reactions; fatigue

Interactions

Insulin or insulin secretagogues (e.g. sulfonylureas): increased hypoglycaemia risk — consider reducing their dose
Oral medications: delayed gastric emptying may affect absorption — caution with narrow-therapeutic-index drugs (e.g. warfarin)
Oral hormonal contraceptives: switch to a non-oral method or add a barrier method for 4 weeks after initiation and after each dose escalation

Clinical monograph

How it works

It is a dual agonist of both the glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) receptors, enhancing glucose-dependent insulin secretion, suppressing glucagon, slowing gastric emptying, and reducing appetite.

Prescribing in practice

When combined with a sulfonylurea or insulin it increases the risk of hypoglycaemia, so a dose reduction of the insulin or sulfonylurea should be considered.
Gastrointestinal effects such as nausea, vomiting, and diarrhoea are common, especially during dose escalation, and acute pancreatitis has been reported, so persistent severe abdominal pain should be investigated.
It is not a treatment for type 1 diabetes or diabetic ketoacidosis, and is generally avoided in pregnancy.

Monitoring

Monitor HbA1c and glycaemic response, body weight, and gastrointestinal tolerability, and review for symptoms suggestive of pancreatitis or gallbladder disease.

Counselling the patient

Inject under the skin once weekly, on the same day each week, rotating injection sites.
Nausea is common at first and usually settles; report severe or persistent abdominal pain.
Tell your clinician if you become pregnant or are planning pregnancy.

Evidence & guidelines

Glycaemic and weight-loss efficacy were demonstrated in a large randomised controlled trial programme supporting its approval in type 2 diabetes and weight management.

Reference: MHRA Approval Mounjaro May 2023; Frias et al. NEJM 2021 (SURPASS-2); Jastreboff et al. NEJM 2022 (SURMOUNT-1); SPC Mounjaro; NICE TA924 (Tirzepatide for T2DM); Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways