3.2 The GLP-1s

Length of treatment and likely responders

Licensed indications do not specify a maximum period of use. NICE guidance specifies a maximum period of two years for NHS use. SPCs advise considering stopping a GLP-1 medicine if less than 5% of the person’s weight has been lost after six months of treatment — this might be 10-15% of people who start treatment.

Experience to date suggests a number of factors that might be involved including:

• Cost of buying treatment privately may mean that the person cannot afford to use the GLP-1 at the recommended dose or sufficiently regularly
• Undiagnosed conditions including hypothyroidism, sleep apnoea/chronic insomnia and eating disorders. In patients with type 2 diabetes, the ability of the pancreas to respond to the GLP-1 is reduced, resulting in a less potent effect than in people who do not have diabetes
• Concurrent medicines may be contributing to less weight being lost
• Unaddressed emotional and psychological aspects could also be having powerful effects and may need appropriate referral
• The six-month period assumes that dosage increases have proceeded according to the intended four-weekly change and for some people this may not have been possible or has taken place over a more extended period due to side effects.

Concerns to be aware of when safely delivering a medicated weight loss service

Muscle loss

Studies suggest that weight loss with GLP-1s over a 36-72 week period may lead to a decrease in non-fat mass of 25-39%, much greater than from weight loss using calorie-restriction alone. The importance of muscle for health and longevity is now well established and pharmacy support helps to ensure protein intake and strength-building physical activity to avoid muscle loss.

Unintended pregnancy

The MHRA issued an alert in June 2025, saying that 40 unintended pregnancies in women taking GLP-1s had been reported to them, 26 of whom were using tirzepatide. 

Malnutrition

Energy dense but nutrient poor foods contribute to a ‘double burden’ of malnutrition in people with obesity. People using GLP-1s may be at risk of malnutrition, particularly if they are significantly restricting their food intake in the hope of speeding up weight loss, and are not being supported and monitored during their treatment.

‘GLP-1 face’ and premature facial ageing 

Rapid weight loss is associated with reduction in both fat and muscle in the face with hollowing, sagging, increased facial wrinkles and a gaunt appearance. Slower and more gradual weight loss (1-2lb per week) is advised as well as keeping up adequate protein intake.