Tirzepatide, branded as Mounjaro®, is the newest weight loss injection on the market and was approved by the UK Government for weight management and loss in November 2023.1 The UK Government has now authorized the use of this medication for weight management purposes in adults with a BMI of 30 kg/m2 or more, as well as a BMI between 27 and 30 kg/m2 if someone also has other health problems related to weight such as prediabetes, high blood pressure, high cholesterol or heart problems. 1 The safety and effectiveness of tirzepatide have NOT YET been established in people under 18 years of age.2 This medicine has been used in the NHS to treat type 2 diabetes since October 2023 and is expected to be available through the NHS for weight management purposes in early 2025.3, 4 private GPs can already prescribe this medicine for both conditions.
How it works (5)
Tirzepatide is a weekly injection that binds to and activates both glucose-dependent insulinotropic polypeptide (also called gastric inhibitory polypeptide or GIP) and glucagon-like peptide-1 (GLP-1) receptors in the body. This means:
- Helps the body release more insulin when blood sugar is high.
- Makes the body more sensitive to insulin.
- Stops the liver from producing and releasing too much glucose.
- Slows how quickly food leaves the stomach, reducing hunger and increasing satiety. It can help people eat less and lose weight.
Tirzepatide is available in doses ranging from 2.5 to 15 mg.
Tirzepatide versus other weight loss injections
Older weight loss injections like semaglutide and liraglutide only activate GPL-1 receptors in the body, while tirzepatide activates both GPL-1 AND GIP receptors. This dual action of tirzepatide is believed to be why it is more effective than other brands in reducing weight and blood sugar.6 Tirzepatide is therefore considered to offer better value for money. 7
For people taking tirzepatide: (8)
- 81.8% lost 5% or more of their body weight,
- 62.1% lost 10% or more of their body weight and
- 42.3% lost 15% or more of their body weight in 365 days.
- The average weight loss was 15.3% at 12 months.
For those taking semaglutide: (8)
- 66.5% lost 5% or more of their body weight,
- 37.1% lost 10% or more of their body weight, and
- 18.1% lost 15% or more of their body weight in 365 days.
- The average weight loss was 8.3% at 12 months.
When semaglutide is stopped, people tend to regain 2/3 of the weight they lost within 68 weeks. Tirzepatide hasn’t been researched in the same way, but in people who lost 21% of their body weight after 36 weeks, they then regained 14% of that weight by week 88 if they stopped to take tirzepatide. 10 Long-term use of these medications is therefore encouraged.
Effect on muscle mass (11, 12)
Although there are no specific statistics on tirzepatide, research has shown that 25-40% of the weight lost on GLP-1 weight loss drugs is fat-free skeletal muscle/mass. The clinical significance of this is not yet clear, but preliminary evidence suggests that it may be related to reduced muscle fat infiltration (which is actually beneficial). However, certain populations are at higher risk of sarcopenia and impaired muscle function and will require additional monitoring and support. For example, those who are older, get little or no exercise, have poor nutritional status, and/or have a serious illness. Changing a person’s diet in favor of moderate protein intake is therefore essential in these groups to preserve lean body mass. Endurance and resistance exercises can also help preserve muscle mass, but fatigue caused by GLP-1 receptor agonists can make this difficult.
Is tirzepatide available on the NHS?
NICE plans to publish its advice on the use of tirzepatide for weight management on 19/12/2024.4 This drug will be rolled out gradually at first, and the first recipients will need to have a BMI above 40 kg/m2 and at minus THREE of the specified values. weight-related health problems: hypertension, dyslipidemia, obstructive sleep apnea or cardiovascular disease.13
Risks and side effects (1,2, 14, 15)
Tirzepatide has side effects similar to other weight loss injections.
- Affects drug absorption – Due to the delay in gastric emptying caused by tirzepatide, it may reduce the absorption of medications taken by mouth. For this reason, women using oral contraceptives should either use an additional barrier method of contraception or switch to a non-oral form of contraception, for the first four weeks when starting tirzepatide, and for four weeks whenever the dose is changed. . Patients taking drugs that depend on a threshold concentration or require a narrow therapeutic index will need to be monitored more closely.
- Gastrointestinal symptoms – These are the most common side effects of tirzepatide and include nausea (affecting 12-20% of people), diarrhea (12-17%), decreased appetite (5-11%), vomiting ( 5 to 9%), constipation (6 to 7%), dyspepsia (5 to 8%) and abdominal pain (5 to 6%). These symptoms tend to diminish over time. Tirzepatide should not be used in clients with gastroparesis.
- Acute pancreatitis
- Hypoglycemia – if someone is also taking sulfonylureas or insulin at the same time. It should not be used in people with type 1 diabetes.
- Serious allergic reaction (e.g. itching, eczema, anaphylaxis).
- Acute kidney injury – in people with pre-existing kidney problems who then suffer from dehydration due to diarrhea, nausea and/or vomiting.
- Vision changes.
- Acute gallbladder disease (in 0.6% of patients).
- This medication causes C-cell tumors of the thyroid, including thyroid cancer. in advice. It is not known whether this medication causes the same effect in humans. Do not use in people with medullary thyroid carcinoma (MTC) or multiple endocrine neoplasia syndrome type 2 (MEN 2) or who have a family history of these conditions.
Should clients who use weight loss injections still consult a dietitian? (16)
Absolutely! Obese clients are at high risk of malnutrition, and nutritional deficiencies are common in this population (even more so after major trauma). Reduced food consumption due to taking anti-obesity drugs can therefore further increase the risk of malnutrition.
Medical nutritional therapy by a dietician is therefore necessary in addition to anti-obesity medications for:
- detect malnutrition and nutritional deficiencies,
- ensure adequate intake of proteins, fluids, fiber and micronutrients (despite a low calorie intake),
- provide specific advice to minimize muscle and bone loss,
- monitor and/or report any gastrointestinal problems, mood changes, disordered eating behavior or other complications to the GP, and
- Liaise with GP regarding medication dose adjustments as weight decreases (e.g. antihypertensives, antidiabetics, diuretics or thyroid medications).
The recommended frequency of dietary intake, alongside anti-obesity medications, is monthly appointments while the dose is adjusted, then every 3 months until goals are achieved. Intake can be further reduced during weight maintenance.
To refer a case management or dispute client for a full dietary assessment and report, contact Specialist Nutrition Rehab on 0121 384 7087 or [email protected].
For more information on the safety and effectiveness of semaglutide and liraglutide, please see our previous article: Pharmaceutical Injections for Weight Loss…Do They Work?