Got a cold while using slimming jabs? Steer clear of common flu meds, pharmacist warns, due to risk of potentially fatal side effects - here's what to take instead

It's likely to happen at least once in the coming months for most Britons: catching a wretched, miserable cold.

For most of us, this means hunkering down and putting our faith in a collection of flu remedies. 

But, for the 1.6million UK adults taking weight loss injections such as Mounjaro and Wegovy, experts warn this could result in serious harm.

According to Dr Dean Eggitt, a senior GP in Doncaster, many common remedies could make side effects of the drugs worse. 

'These medications affect absorption of medicines that are swallowed,' he explains. 'Not only does this affect how well medicines work, but it may also increase the risk of unexpected side effects.' 

What's more, respiratory infections themselves can be more dangerous to those on the jabs - which mimic the appetite-suppressant hormone GLP-1. 

'GLP-1 drugs effectively mute thirst, increasing dehydration risk,' says Dr Eggitt. 'And this combined with the dehydrating effects of illness could be a lethal combination.'

With this in mind, we asked some of the country's top experts which cold and flu medications you should avoid if you're using slimming jabs.

As temperatures drop, cold and flu season is making an unwelcome return

Nurofen could be bad news for your kidneys 

Anti-inflammatory painkillers such as ibuprofen and naproxen should be used with caution, say experts. 

This includes over-the-counter remedies that combine ibuprofen with a decongestant, like Nurofen cold and flu relief. 

The medication, known as non-steroidal anti-inflammatory drugs (NSAIDs), can increase the risk of acute kidney injury in people who are dehydrated - which is common in slimming jab users. 

This is because the drugs work by blocking compounds involved in inflammation, but those same compounds also help maintain blood flow to the kidneys.  

This effect, accompanied by dehydration that impacts the organ's ability to function, can trigger serious damage. 

Rachel Jones, pharmacy superintendent at Superdrug, said: 'Dehydration is one of the biggest risks to be aware of when taking weight loss treatments, particularly during cold and flu season.

'Weight loss treatments can cause gastrointestinal side effects, especially when someone first starts treatment.

'If you then develop flu or a stomach bug, symptoms such as fever, sweating, vomiting and diarrhoea can cause further fluid loss.'

Common signs of dehydration include dark urine, dizziness, headaches, dry mouth and passing urine less often than usual. 

Severe dehydration can also cause confusion, extreme tiredness and a rapid heartbeat.

Cold remedies that help you sleep might be a problem 

Some types of antihistamines are also not advised for those using weight loss jabs.

This includes diphenhydramine, the sedating ingredient found in products such as Benadryl, Nytol and Boots Sleepeaze, which may worsen another common side effect of GLP-1 medications - constipation.

This is because the compound blocks the natural chemical signals that tell your gut to move. 

As a result, the muscles in your intestines relax, which slows down digestion and delays bowel movements.

Complications of constipation include haemorrhoids and anal fissures. 

In rare and severe cases, hard stool can completely block the bowel or create tears in the colon wall that require emergency treatment.

Careful of Lemsip if you're eating very little 

Many cold and flu remedies contain oral decongestants like phenylephrine and pseudoephedrine alongside ingredients like paracetamol.

The drugs aim to narrow the swollen blood vessels in nasal passages and sinuses, reducing the pressure in the area. 

But they also stimulate the central nervous system, triggering an adrenaline-like response that can raise blood sugar levels.

As many slimming jab users suffer type 2 diabetes, and already struggle to keep blood sugar levels stable, experts advise these patients to monitor their sugar levels extra closely while taking decongestants - or avoid them altogether.

The pills can also exacerbate feelings of anxiety and 'jitteriness' that are common in people using fat jabs. 

Dr Deborah Lee from Dr Fox Online Pharmacy adds: 'Decongestants such as pseudoephedrine can cause a racing heart, jitters and feelings of anxiety, which may be more noticeable in people taking GLP-1 drugs, particularly if they are eating very little.' 

Many specific cold and flu remedies contain oral decongestants alongside ingredients like paracetamol

Multi-symptom sugar syrups could trigger sickness 

Doctors also advise caution with multi-symptom cold and flu products that contain multiple active ingredients in a single sachet or capsule.

These medicines often combine painkillers, decongestants, antihistamines and cough suppressants, meaning patients may end up taking ingredients they do not actually need.

For people already experiencing nausea, constipation or stomach upset from GLP-1 medications, this can increase the risk of unwanted side effects.

What's more, Dr Lee adds that syrups, powders and lozenges can contain significant amounts of sugar, which may sit in the stomach for longer because GLP-1 drugs delay gastric emptying, potentially worsening bloating or nausea. 

'Rather than reaching for an all-in-one remedy, it's often safer and more effective to treat the symptom you actually have, whether that's pain, congestion or a runny nose,' she says. 

What should you take instead?

Paracetamol is generally considered a safer option for treating fever, headaches and aches and pains.

According to the NHS, the maximum recommended dose for adults is two 500mg tablets, up to four times in 24 hours. Taking more than this can increase the risk of serious liver damage.

Ms Jones says: 'For people taking weight loss treatments, I'd generally recommend choosing simple treatments that target individual symptoms rather than automatically reaching for an all-in-one cold and flu remedy. 

'For a fever, headache or body aches, paracetamol is often a suitable first option for many people, provided it's taken according to the instructions and isn't being taken alongside other medicines containing the same ingredient.'

If you're suffering from a blocked nose, she recommends a saline nasal spray to help ease congestion without adding unnecessary medication. 

For a cough or sore throat, soothing lozenges, warm drinks and appropriate cough remedies may also help ease discomfort.

'Ultimately, I'd encourage anyone taking weight loss medication to speak to their pharmacist before choosing an over-the-counter treatment, particularly if they're experiencing side effects or taking other medicines,' she says. 

'A pharmacist can help identify the most suitable option based on their symptoms and individual health needs.'

When to skip a dose and see a GP 

'It's common practice to have sick day rules with many medications - GLP-1s included,' says Dr Eggit. 

'If you are ill and not drinking much and are therefore at risk of dehydration, omitting the medicine is useful.'

However, he says severe stomach upset whilst using a GLP-1 is a sign to seek urgent medical help.

'We are seeing that GLP-1s are associated with the life-threatening condition called pancreatitis, where the pancreas becomes irritated and leaks some very corrosive fluids,' he says.

'Anyone with abdominal pain should stop taking the medicine immediately and seek medical assistance.

'You should also seek urgent medical advice if you're unable to keep fluids down, show signs of dehydration or develop severe stomach pain.' 

If you're about to begin Wegovy or Mounjaro, experts suggest waiting until you've recovered from a cold or flu, as both illnesses and GLP-1 drugs can cause nausea and stomach upset.