Patient information · General health
Weight loss injections
what they do, and what they do not
GLP-1 medications are the most effective weight loss drugs ever available and they have changed what is achievable. They are also widely oversold. This leaflet sets out what the evidence shows, including the parts that are less often mentioned: muscle loss, cost, side effects, and what happens when you stop.
Stop and seek medical help urgently if you develop
- severe, persistent abdominal pain, especially spreading to the back with vomiting — this may be pancreatitis
- signs of dehydration from prolonged vomiting or diarrhoea
- severe upper right abdominal pain with fever or jaundice — possible gallbladder problem
- a lump in the neck, hoarseness, or difficulty swallowing
- vision changes, or symptoms of very low blood sugar if you also take insulin or a sulfonylurea
Nausea is expected; severe unrelenting abdominal pain is not. In an emergency call 999, or go to the Royal London Hospital Emergency Department, Whitechapel Road, London E1 1FR.
How they work
They mimic gut hormones released after eating. They slow stomach emptying, act on appetite centres in the brain, and for most people substantially reduce hunger and the constant background preoccupation with food that many describe as 'food noise'. They are given as a weekly injection, with the dose increased in steps over several months.
Those are averages. Some people lose considerably more, and around one in ten loses very little — which is worth knowing before starting, and a reason to review at three to four months rather than continuing indefinitely without benefit.
Side effects
- Nausea, vomiting, constipation, diarrhoea, reflux and burping are common, usually worst after each dose increase, and usually settle.
- Eat smaller portions, stop when full rather than when the plate is empty, avoid fatty and heavy meals, and keep fluids up.
- Gallstones are more common, partly because rapid weight loss itself causes them.
- Pancreatitis is uncommon but serious.
- Injection site reactions, fatigue and hair thinning during rapid loss.
- They interact with other diabetes medication and can affect absorption of other tablets.
Muscle loss is the part that gets least attention
Around a quarter to a third of the weight lost on these medications is lean tissue rather than fat. That matters for strength, metabolic rate and, in older people, frailty and falls. It is largely preventable: eat adequate protein at every meal — considerably more than you might expect while eating less overall — and do resistance training at least twice a week throughout. If you take nothing else from this leaflet, take that.
When you stop
This is not a course of treatment with an endpoint. Trials consistently show that most of the weight returns over the following one to two years after stopping, along with the improvements in blood pressure and blood glucose. The medication treats the condition while it is being taken, in the way blood pressure tablets do.
That has practical implications worth thinking through before you start: the likely long-term cost, whether you will be able to continue, and what your plan is if you stop. Using the period on treatment to build eating patterns, activity and strength that can persist afterwards gives the best chance of holding some of the benefit.
Who should not take them
- anyone pregnant, planning pregnancy or breastfeeding — and note these medications can reduce the effectiveness of oral contraception, so additional contraception is needed
- a personal or family history of medullary thyroid cancer or MEN2
- previous pancreatitis
- severe gastrointestinal disease or gastroparesis
- anyone with a current or past eating disorder, without specialist input
- people seeking cosmetic weight loss at a healthy weight
Buying online
These medications are prescription-only for good reason. Products bought from unregulated websites and social media sellers are frequently counterfeit, incorrectly dosed or contain something else entirely, and people have been seriously harmed. Anyone prescribing them should be checking your history, weight, blood tests and progress — not simply taking a payment.
Book an appointment if you want to discuss whether these medications are appropriate for you. We assess suitability properly, arrange baseline blood tests, prescribe and titrate with regular review, and provide the dietary and strength-training support that determines whether the weight you lose is fat rather than muscle.
Assessed, prescribed and monitored properly
Seven days a week, 9am–7pm, on Whitechapel Road.
Tower Bridge Hospital London
97–99 Whitechapel Road, London E1 1DT
WhatsApp 07903 284 189
info@mhwclinic.co.uk
Open Mon–Sat, 9am–7pm (closed Sundays until September)
In an emergency
Call 999, or go to the Royal London Hospital Emergency Department, Whitechapel Road, London E1 1FR.
When we are closed and it is not an emergency
Call NHS 111 or visit 111.nhs.uk.