GLP-1 is a naturally occurring hormone in the body usually released after you eat. It does 3 things: sends a signal to your brain that you are full, slows down the emptying of your stomach which leaves you fuller for longer, and reduces your blood sugar levels by improving how your body produces insulin.

Semaglutide (Wegovy) and Tirzepatide (Mounjaro) are GLP-1 receptor agonists drugs which means they mimic the actions of GLP1 hormone, and work by acting on receptors in your brain that make you feel fuller and less hungry.

Semaglutide (Wegovy) and Tirzepatide (Mounjaro) are GLP-1 receptor agonists drugs which means they mimic the actions of GLP1 hormone. They are very similar in how they work but Mounjaro is a dual agonist which means it mimics two hormones (glucose‐dependent insulinotropic polypeptide (GIP) and GLP-1).

The drugs also have different starting doses and following a different dose escalation protocol, but they both are effective in weight loss management and have similar side effects.

People who are suitable for GLP1 medication include:

• Adult >18 years old, with BMI >30, or
• Adult > 18 years old with BMI > 27 with at least one other weight-related condition, such as high cholesterol, high blood pressure, pre-diabetes, sleep apnoea, history of heart attack, stroke or blood vessel disease.

If your BMI is significantly different to the drug licence, you may not be eligible for the treatment.

You cannot take GLP1 drugs if you have any of the following conditions:

• Type 1 diabetes
• Diabetic retinopathy/diabetic eye disease
• History of pancreatitis
• Personal or family history of thyroid cancer
• Personal or family history of Multiple Endocrine Neoplasia type 2 (MEN2)
• Inflammatory bowel disease (IBD)
• Gastroparesis, or delayed emptying of the stomach
• Kidney disease
• Pregnant or trying to become pregnant
• Breast-feeding (tirzepatide is present in breast milk)
• Previous allergic reactions to GLP1 drugs

Both Wegovy or Mounjaro are taken once a week, at the same time and day. The main difference is that Mounjaro (tirzepatide) dosage starts at 2.5 mg and can be increased to a maximum dose of 15 mg. Wegovy (semaglutide) dosage starts at 0.25 mg and is increased to a maximum maintenance dose of 2.4 mg.

Both dosage schedules follow a 4-weekly plan, increasing the dose every 4 weeks if there are no serious side effects. The medications are injected under the skin (subcutaneous) usually in the stomach area, thighs or upper arms. While this might sound challenging, it is very straightforward.

All medications may cause side effects, and our consultant conducts a comprehensive assessment before prescribing GLP-1 medications. Some side effects are very common (may affect more than 1 in 10 people). These are usually mild to moderate and usually go away over time. These side effects may include:

• headache
• feeling sick (nausea)
• being sick (vomiting)
• diarrhoea
• constipation
• stomach pain
• feeling weak or tired.

Other side effects may include:

• burping
• gas
• bloating
• heartburn
• hair loss

Rarer and more serious side effects may include:

• inflammation of the pancreas (pancreatitis)
• gallbladder (cholecystitis)
• low blood sugar (hypogylycemia)
• allergic reactions.