Are weight loss injections ruining your health? 

Are you one of the 1.5 million [1] currently taking weight loss injections in the UK?  

Injections like Mounjaro (tirzepatide), Wegovy and Ozempic (semaglutide) are everywhere right now – approved by the National Institute for Health and Care Excellence (NICE) [2] for eligible adults and increasingly offered in NHS services and private clinics.

While these injections are widely acknowledged to help with weight loss, what’s less well known are the potential side effects.

We’ll explain what to watch out for, what to do about any health concerns, and how to move forward safely.

 

What are GLP-1s?

 

Glucagon-like peptides (GLP-1) are medicines that mimic the gut hormone peptide-1, helping you feel fuller for longer by slowing stomach emptying, reducing appetite, and steadying blood sugar levels. They are typically taken as a weekly injection.  

You should note that, due to slowing digestion, weight loss injections may affect the effectiveness of oral contraceptives. 
 
While these injections help curb appetites and support healthy weight loss, it’s essential to recognise when side effects may signal a more serious issue. 

To find out more about how GLP-1s work, read our guide to weight loss injections.  
 

 

Your body’s response to GLP-1s – a closer look

 

Weight loss medicine can be an effective tool, but it's also essential to understand the warning signs that require attention. We take a deeper look at potential GLP-1 issues.

Pancreatitis risk

GLP-1 weight loss injections can, in a few cases, irritate the pancreas and triggeracute pancreatitis. If you suffer from gall bladder issues, GLP-1s may slow down the rate at which the gall bladder empties, increasing the chance of gallstones – a common cause of pancreatitis [3]

If you develop severe, persistent upper-abdominal pain – often radiating to your back, accompanied by nausea or vomiting, that’s a red flag for acute pancreatitis and needs urgent medical care. A simple lipase blood test helps doctors quickly detect this condition. Lipase is a digestive enzyme released by an inflamed pancreas and is typically an early marker, making it a front-line rule-out test [4].

If pancreatitis is suspected, guidelines advise stopping the injections immediately until you’re assessed.

Liver stress

GLP-1 injections can stress the liver indirectly by raising the risk of gallbladder or biliary issues. When bile flow is blocked or sluggish, blood tests often show one of two patterns:

• Cholestatic (bile-flow) pattern: Liver enzymes alkaline phosphatase (ALP) and gamma-glutamyl transferase (GGT), rise more than alanine transferase (ALT) and aspartate aminotransferase (AST). Bilirubin may also increase if there’s a blockage, indicating a bile-duct issue such as gallstones.
• Hepatocellular (liver-cell) pattern: ALT levels rise more than ALP levels, suggesting inflamed liver cells from a range of possible causes [5].

If you start to experience pain under the right ribs or in the upper abdomen, moving to the back, dark urine, pale stools, itching, fever, or yellow eyes and skin (jaundice), seek urgent medical attention.  
 
Check your bilirubin, GGT, ALP, and ALT levels with our at-home Liver Function Blood Test.  

Kidney strain and dehydration 

GLP-1 can trigger nausea, vomiting and diarrhoea, which may lead to dehydration; this, in turn, can reduce kidney function, increase urea and creatinine, and result in acute kidney injury. Doctors will often check glomerular filtration rates (eGFR) to assess how well the kidneys are filtering your blood.

Individuals with pre-existing kidney problems are more susceptible to kidney strain.

If you experience the need to urinate less frequently, dark-coloured urine, persistent vomiting, diarrhoea, dizziness, confusion, or extreme tiredness, you should seek urgent medical advice [6]. 

Monitor your kidney function by checking for increased urea and creatinine levels with our Kidney Blood Test. 

Diabetes risk 

 GLP-1 weight-loss injections often improve long-term glucose control, and trials show meaningful HbA1c reductions alongside weight loss [7]. HbA1c is your 3-month average blood sugar, so a reduction confirms a real metabolic win. However, several risks are associated with GLP-1 for people with diabetes. 

While hypoglycemia (low blood sugar) is uncommon with GLP-1s on their own, the risk increases if you also use insulin or sulfonylurea. Watch for symptoms such as sweating, shaking, palpitations, and confusion, and adjust your diabetes medications as needed [8]. You should treat any symptoms promptly with fast-acting carbs and seek help if they persist. 

In people with existing diabetic retinopathy, rapid HbA1c improvements are linked with retinopathy complications [9]. If you experience blurred vision or increased floaters, seek prompt medical advice. 

Our Diabetes (HbA1c) Blood Test checks your average blood sugar levels over the previous 3 months and helps detect pre-diabetes and type 2 diabetes. Monitoring these levels is essential, especially if you’re using weight loss injections.  

Heart-health impact 

Weight loss injections can reduce the risk of heart disease by promoting weight loss. In people who are overweight or have cardiovascular disease, weekly semaglutide injections reduced major adverse cardiovascular events [10].

However, there are potential heart-related downsides to be aware of. 

GLP-1s can nudge resting pulse rates up by around 1–4 bpm on average, and some individuals experience nausea, vomiting, or diarrhoea, leading to dehydration. These can all stress your cardiovascular system. If you experience a sustained racing or pounding heartbeat at rest, or feel dizzy or lightheaded, seek medical advice. 

Even with weight loss, non-HDL cholesterol or triglycerides may remain high. A full lipid profile, including total cholesterol, LDL, non-HDL, HDL, and triglycerides, can help assess potential risks and determine the best course of action – dietary changes, lifestyle modifications, or statin therapy [11].

Our Cholesterol Blood Test provides a full lipid profile, enabling you to monitor your levels and make informed decisions. Additionally, our article on non-HDL cholesterol offers a deeper understanding.

Iron levels

GLP-1 injections can indirectly worsen iron status for some people. They suppress appetite and slow stomach emptying, so total intake of iron-rich foods may drop, and absorption reduced. Add commonly seen GI side effects – nausea, vomiting, diarrhoea, or constipation, and the risk of dietary shortfalls rises. 

Persistent fatigue, shortness of breath, palpitations, pale skin, or frequent headaches are classic signs of iron deficiency, which can lead to anaemia.

Our Iron Blood Test checks for deficiencies using several markers, including ferritin, a protein that stores iron in your cells and tissues. 

 

Nutrient deficiencies

As GLP-1 weight loss injections prevent you from feeling hungry and slow stomach emptying, many people eat less protein and micronutrients than they require. Rapid weight loss also reduces lean muscle mass alongside fat. Over time, that can raise the risk of sarcopenia – an age-related, degenerative disease characterised by a progressive loss of muscle mass, strength, and function. 

The risk climbs further if someone simply eats smaller portions of ultra-processed foods (UPFs). UPFs are nutrient-poor, so eating small meals of UPFs won’t address any protein, fibre, iron, or vitamin shortfalls [12].

If you’re suffering from persistent fatigue, hair loss, brittle nails, skin issues, frequent infections, slower recovery from exercise, or strength loss, you could have protein or micronutrient gaps.

Read our guide to naturally improving your GLP-1 levels through nutrition to discover more.

 

Weight loss injections can be effective and safe for the right person, but they’re not a set-and-forget solution. Know the red flags, stay vigilant with simple checks, and pair the medicine with solid fundamentals – protein, whole foods, regular movement, and quality sleep. If something feels off, pause your injections and speak to your doctor.  

If you want to look after your health while on weight loss injections, but feel overwhelmed by all the options, we’ve got your back. Our Weight Loss Injection (GLP-1) Monitoring Blood Test tracks the right biomarkers to turn guesses into a clear, safe plan.

 

 

Weight loss injection FAQs

 

1. Are weight loss injections safe long-term?

Evidence suggests that GLP-1 weight-loss injections can be safe and effective in the long term for the right individuals, when prescribed and monitored by a doctor. Ongoing follow-ups are important because long-term data is still evolving. 
 

2. Can weight loss injections damage your gut?

Weight loss injections commonly cause tummy side effects, such as nausea, vomiting, diarrhoea, or constipation and slow stomach emptying. Most issues improve with slow dose increases and diet tweaks, but seek urgent care for severe, persistent stomach pain, vomiting, or inability to keep fluids down. 
 

3. What happens when you stop Wegovy/Mounjaro/Ozempic?

When you stop receiving weight loss injections, your appetite usually returns, and weight can creep back without a well-established diet, exercise plan, and sleep routine in place. Blood sugars may rise again if you have diabetes. Most side effects subside, but consult your doctor about discontinuing or switching medications, and continue to monitor your weight, HbA1c/glucose levels, and lipids. 
 

4. Can I drink alcohol on GLP-1 weight loss injections?

Alcohol can worsen nausea, dehydration, and pancreatitis risk (and trigger hypoglycaemia if you use insulin/sulfonylureas). Limit or avoid it during dose increases or if you experience tummy symptoms. Hydrate well and consult your doctor if you are unsure. 
 

5. Do weight loss injections affect fertility?

Research is underway to determine the effect of weight loss injections on fertility as this is unknown at present [13]. However, there is evidence to suggest that the injections may affect the effectiveness of oral contraceptives [14], and they are not suitable to be taken while pregnant or breastfeeding. Discuss with your doctor when to stop taking your injections before trying to conceive. 
 

References

 

1. Triggle, N. and Roxby, P. (2025)Weight-loss injections: How do drugs like Wegovy and mounjaro work?, BBC News (Accessed 21 September 2025).  

2. NICE (2024) Tirzepatide for managing overweight and obesity, (Accessed 21 September 2025).  

3. He L, Wang J, Ping F, Yang N, Huang J, Li Y, Xu L, Li W, Zhang H. (2022) ‘Association of GLP-1 receptor agonist use with risk of gallbladder or biliary disease’, JAMA Internal Medicine. (Accessed 22 September 2025).

4. NHS (2022) Acute pancreatitis. National Health Service. (Accessed 22 September 2025).

5. Specialist Pharmacy Service (2024), Assessing liver function and interpreting liver blood tests. (Accessed 22 September 2025).

6. NHS (2018) Acute kidney injury (AKI) — symptoms and when to seek help. (Accessed 22 September 2025). 

7. Capehorn, M. (2020) Once-weekly semaglutide reduces HbA1c and body weight, Diabetes Therapy, summary of SUSTAIN programme. (Accessed 23 September 2025). 

8. Diabetes UK (n.d.) What is HbA1c? (Accessed 23 September 2025)

9. FDA (2025) Wegovy (semaglutide) Prescribing Information — warnings on hypoglycaemia with insulin/sulfonylurea and monitoring retinopathy. (Accessed 23 September 2025). 

10. A. Michael Lincoff, M.D., Kirstine Brown-Frandsen, M.D., Helen M. Colhoun, M.D., John Deanfield, M.D., Scott S. Emerson, M.D., PhD, Sille Esbjerg, M.Sc., Søren Hardt-Lindberg, M.D., PhD, G. Kees Hovingh, M.D., PhD, Steven E. Kahn, M.B., Ch.B., Robert F. Kushner, M.D., Ildiko Lingvay, M.D., M.P.H., Tugce K. Oral, M.D., Marie M. Michelsen, M.D., Ph.D., Jorge Plutzky, M.D., Christoffer W. Tornøe, PhD, and Donna H. Ryan, M.D., (2023) Semaglutide and cardiovascular outcomes in obesity without diabetes, New England Journal of Medicine, 389, pp. 2221–2232. (Accessed 23 September 2025).

11. BHF (2024) Understanding your cholesterol levels. British Heart Foundation. (Accessed 23 September 2025).

12. Neff, T., (2025) Nutrition is vital when taking GLP-1 weight loss drugs. UCHealth. (Accessed 23 September 2025).

13.  NHS (2025) New research to explore weight loss injections pre-pregnancy (Accessed 25 September 2025).

14. Roxby, P., Bailey, E., Women warned weight-loss jabs may affect the pill, BBC News, (Accessed 25 September 2025)