GLP-1 receptor agonists and tirzepatide: an overview of the class

What incretin-based medicines are

After a meal, the intestine releases hormones called incretins, chiefly GLP-1 (glucagon-like peptide-1) and GIP (glucose-dependent insulinotropic polypeptide). They tell the pancreas to release insulin when glucose is high, suppress glucagon, slow the emptying of the stomach and act on appetite centres in the brain. Natural GLP-1 is broken down within minutes. The medicines in this guide are engineered versions that resist that breakdown and remain active for a day or, in most cases, a week.

The four medicines

Active substance	Class	Brand names	Dosing
Semaglutide	GLP-1 receptor agonist	Ozempic, Wegovy (injection); Rybelsus (tablet)	Once weekly (injection); once daily (tablet)
Liraglutide	GLP-1 receptor agonist	Victoza, Saxenda; Xultophy (with insulin degludec)	Once daily
Dulaglutide	GLP-1 receptor agonist	Trulicity	Once weekly
Tirzepatide	Dual GIP/GLP-1 receptor co-agonist	Mounjaro, Zepbound	Once weekly

Semaglutide, liraglutide and dulaglutide act on the GLP-1 receptor only. Tirzepatide activates both the GLP-1 and the GIP receptor, which is why it is called a co-agonist rather than a GLP-1 receptor agonist; it is grouped with the class because its mechanism, dosing pattern and warnings overlap so closely.

What they are approved for

The approved uses differ by product and by country, and they have been expanded several times in recent years. In broad terms:

• Type 2 diabetes: all four are approved to improve glycaemic control in adults with type 2 diabetes, alongside diet and exercise, alone or in combination with other glucose-lowering medicines.
• Chronic weight management: semaglutide (as Wegovy), liraglutide (as Saxenda) and tirzepatide (as Zepbound in the US, Mounjaro in the EU) are approved as an adjunct to diet and physical activity in adults with obesity, or overweight with a weight-related condition; some are also approved in adolescents.
• Cardiovascular risk reduction: semaglutide, liraglutide and dulaglutide carry indications to reduce the risk of major cardiovascular events in defined patient groups.
• Further indications for semaglutide include chronic kidney disease in type 2 diabetes and, since 2025, metabolic dysfunction-associated steatohepatitis (MASH). Tirzepatide is additionally approved in the US for obstructive sleep apnoea in adults with obesity.

The medication page for each product lists the current indications in detail, together with its source and the date it was last reviewed.

How they are taken

All four injectable products are supplied in pre-filled pens for subcutaneous injection into the abdomen, thigh or upper arm. Treatment starts at a low dose that is not itself therapeutic and is increased in steps of several weeks so that the digestive system adapts; the escalation schedules are printed in the product information and differ between the diabetes and the weight-management products. Rybelsus, the oral form of semaglutide, is taken once daily on an empty stomach with a small amount of water at least 30 minutes before the first food, drink or other medicine of the day.

Storage and shipping

Unopened pens are stored at 2–8 °C and are shipped under cold-chain conditions. Once a pen is in use, the product information allows a limited period at room temperature: for semaglutide 4 to 6 weeks below 30 °C depending on the formulation, for liraglutide 30 days at or below 30 °C, for dulaglutide 14 days below 30 °C and for tirzepatide 21 days below 30 °C. Pens must not be frozen and should be kept with the cap on to protect them from light. Rybelsus tablets are stored at room temperature in the original blister.

Side effects and warnings shared by the class

The most common side effects are gastrointestinal: nausea, diarrhoea, vomiting, constipation and abdominal pain. They are usually mild to moderate, most frequent during dose escalation and tend to lessen over time. Other effects listed in the product information include decreased appetite, headache, fatigue, injection-site reactions, gallstones and a small increase in heart rate. On their own these medicines rarely cause low blood sugar, but the risk rises when they are combined with insulin or a sulfonylurea, and the dose of those medicines may need adjusting.

Warnings that apply across the class include acute pancreatitis, which requires the medicine to be stopped if suspected; gallbladder disease, more common with substantial weight loss; and a temporary worsening of diabetic retinopathy when glucose control improves rapidly, which calls for caution in patients with existing eye disease. The product information advises against use in pregnancy and breastfeeding. Because GLP-1 receptor agonists caused thyroid C-cell tumours in rodent studies, a personal or family history of medullary thyroid carcinoma or multiple endocrine neoplasia type 2 is a contraindication in some jurisdictions and a warning in others.

Compounded and salt-form products

In 2023 the US Food and Drug Administration warned about compounded semaglutide products following adverse event reports, noting that salt forms such as semaglutide sodium or semaglutide acetate have not been shown to be safe or effective. Only finished products from authorised manufacturers carry the evidence summarised above, and only those are handled through our service.

Prescription and sourcing

All four medicines are prescription-only. A valid prescription from a licensed physician is required, and the destination country’s rules on prescription medicines are verified before dispatch. Because several brands of each substance exist and the approved indications differ between them, a request should name the active substance, the brand, the strength and the number of pens.