Initially created to treat diabetes, medications such as Mounjaro and Ozempic have gained fame for their effectiveness in promoting rapid weight loss by diminishing hunger and reducing ‘food noise’.

However, these so-called ‘miracle’ injections can pose significant health risks and may lead to severe, life-threatening side effects, a prominent doctor has cautioned.

These drugs replicate the GLP-1 hormone in the brain, helping to suppress hunger signals, prolong feelings of fullness, and decrease appetite.

Despite their weight loss benefits, studies have connected these medications to various side effects, including digestive problems, blindness, and even organ damage.

Dr. Dean Eggitt, a leading general practitioner and CEO of the Doncaster Local Medical Committee, points out that, “When prescribed through the NHS, the risk is somewhat reduced because your doctor can access your full medical history.”

“However,” he adds, “private healthcare providers often have limited access to your records. If you’re not completely transparent about your other medications, you could be endangering your health.”

‘There is a reason that not everyone can access these drugs, and that’s because it can put some people’s health in jeopardy.’ 

Jason Murphy, head of pharmacy Chemist4U, added: ‘There a number of medical conditions that will completely rule out your ability to prescribed weight loss injections because of the severe risks associated with them.

‘However, other conditions require a bit more careful consideration and may require special assessment to ensure the treatment would be safe and appropriate.’ 

With the so-called wonder drugs coming under scrutiny, we asked health care experts to break down who can’t take GLP-1s and why 

Stomach problems 

Trials of semaglutide—the active ingredient in these drugs—have long flagged gastrointestinal discomfort including nausea, diarrhoea, vomiting and constipation as a common side effect of the drug, affecting up to 75 per cent of users.

As such, Dr Eggitt says the jabs may not be appropriate for people already suffering from inflammatory bowel disease (IBD) or other conditions that affect the digestive system and cause abdominal pain, bloating and diarrhoea. 

‘If you’ve got irritable bowel, you tend to either suffer from constipation or diarrhoea or a bit of both. 

‘If you already suffer from constipation, taking a drug that slows down gut transit time could put you at risk of a physical blockage which can lead to a tear in the bowel wall, resulting in fecal matter leaking into the abdomen.’ 

This is because GLP-1 medications can cause delayed gastric emptying and slows how food moves through the gastrointestinal tract, making stools drier and harder. 

Straining more when opening the bowels, them, in turn, can cause small tears in the bowel lining. 

This can cause peritonitis, which occurs when the lining of the stomach becomes infected. Left untreated, the condition can be life threatening. 

The peritoneum covers internal organs including the kidneys, liver, and bowel, which can become damaged when the lining is infected. 

Eating disorders 

Anorexia is an eating disorder and serious mental health condition characterised by restrictive eating to keep weight a low as possible

Doctors are increasingly worried about GLP-1s being used by people with restrictive eating disorders, Dr Eggitt explained. 

The interactions between these blockbuster jabs and eating disorders are complex, but one of the main concerns is that they could facilitate disordered eating patterns, suppressing appetite and even encouraging purging. 

Because the stomach empties more slowly on these drugs, it can make it easier to expel any food that has been consumed, says Dr Eggitt. 

‘People underestimate eating disorders, and think it’s not that big of a deal but eating disorders can and do kill,’ he warned. 

‘People with restrictive eating disorders often use other medicines to catalyse the weight change. So rather than just food avoidance there’s often laxative use too which leads to dehydration. 

‘If you have someone who is fixated upon losing weight, using a weight loss drug to inhibit an appetite that’s not really there in the first place is essentially dicing with death,’ he added. 

‘This is one of the main problems with distance prescribing, which is allowing too many people to slip through the net and access weight loss drugs which essentially could kill them.’ 

Family history of certain cancers 

‘One of the more serious side effects of weight loss injections is the development of thyroid tumours,’ warned Murphy.

Concerns about thyroid cancer and GLP-1s were first raised in the pre-marketing phase, after a number of animal studies linked the drugs to an increase in thyroid C cell tumours.

Thyroid cancer is one of the 13 cancers known to be linked with obesity, but experts are hesitant to prescribe the drug to those with a family history of the disease. 

Whilst the evidence remains conflicting, one meta-analysis of over 60 studies by Italian researchers published last year found a significant increase in overall thyroid cancer risk.

Conversely, another study published this year found no substantial increase in thyroid cancer risk over an average follow up of nearly four years.

One potential reason for this difference in findings could simply be that patients on GLP-1s are more likely to have a thyroid ultrasound which could pick up existing nodules which could be cancerous. 

Either way, Murphy stressed that is crucial to be honest with your doctor or pharmacist about your history of the disease, so healthcare professionals can make an informed decision.

‘If you have a personal of family history of medullary thyroid cancer or Multiple Endocrine Neoplasia syndrome type 2 (MEN 2), you cannot take weight loss injections as it may put you at greater risk,’ he said. 

Type 1 diabetes 

‘If you are diabetic, weight loss injections can present problems,’ Murphy warned. 

Type 1 diabetes is a condition where your body cannot make a hormone called insulin – which helps the body use glucose for energy

This is because diabetes medication taken by type 1 diabetics to help reduce blood glucose levels can interact with weight loss injections and cause blood sugar levels to become dangerously low, known as hypoglycemia. 

Symptoms include feeling hungry, dizzy and anxious as well heart palpitations which can lead to seizures or fits when blood sugar levels drop severely low. 

He added: ‘It’s incredibly important that, if you are considering taking weight loss injections, your speak to a healthcare professional before doing so and are honest about personal or family history of various medical conditions.’  

Interactions with other medications 

Ozempic and Wegovy, which both contain semaglutide, work by mimicking a hormone called GLP-1 that triggers an increase in insulin production and slows the rate at which food is digested in the stomach.

‘The problem with this is that it reduces the bioavailability of other medicines that are taken orally, increasing absorption time and reducing the drug’s efficacy,’ Dr Eggitt explained.

‘One of these drugs is the combined oral contraceptive pill, which needs to be in the stomach to be absorbed.

‘But some weight loss drugs drastically slow down this process, effectively rendering the drug ineffective, which can be said for a number of other drugs like anti-epileptic medication,’ Dr Eggitt continued.

The MHRA advised women on the jabs to use barrier contraception if they are seeking to avoid pregnancy 

Earlier this year, women using weight-loss drugs were urged to use an alternative effective contraception after dozens reported becoming pregnant while taking the medications. 

The verdict

In the UK, millions of people take the drugs safely, with thousands doing so for years. 

Doctors insist that weight loss jabs will be ‘game changers’ when it comes to fighting back against the ongoing obesity crisis, which costs the economy an estimated £100bn per year.

However, no drug is without risk, experts warn.  

It comes as experts sounded an alarm over the death toll linked to blockbuster weight loss jabs, which surpassed 50 deaths since the beginning of 2024. 

In total, the Medicines and Healthcare products Regulatory Agency (MHRA), which polices the safety of every drug used in Britain, has received 173 ‘reports with fatal outcomes’ from GLP-1 injections. 

Tam Fry, chair of the National Obesity Forum, claimed that although the drugs were hugely effective for those who need them, they were being used ‘inappropriately’ by slimmer adults who ‘fancy losing a bit of weight.’ 

He added: ‘If you take them and you don’t need them, and you break the rules, you run the risk of serious complications – or death.

‘People think “it’s not going to happen to me” but it will happen to them. So they take them and they get severe complications.’

The data, kept by a Government body, does not state whether any of the people who died while using the jabs had been using them inappropriately.

Meanwhile, there are concerns that illegal knock-off versions of the drugs are being increasingly used—often advertised on social media.