Medical negligence
What are the risks of weight loss injections?
Our medical negligence experts explore the risks associated with weight loss drugs in the UK and what considerations should be made if the drug becomes available to you.
Weight loss injections such as Mounjaro and Wegovy have been available on the NHS since March 2025. The drug has marked a new chapter in weight loss, where people can further manage health issues such as obesity and diabetes.
However, since its increased availability, the drug has been subject to concerns about the risks associated with its use. Current warnings for the drug include usage alongside the conceptive pill, and the risks it can present towards pregnant women and their unborn child.
Here, our medical negligence experts explore the risks associated with weight loss drugs in the UK and what considerations should be made if the drug becomes available to you.
What weight loss drugs are available in the UK?
In the NHS, doctors can now prescribe eligible patients two types of weight loss drugs:
- Tirzepatide, sold as Mounjaro
- Semaglutide, sold as Wegovy.
Semaglutide is also used in the common treatment drug ‘Ozempic’ for people with type 2 diabetes.
Both drugs are prescribed as a self-injectable pen in a weight loss plan, to regulate blood sugar and energy levels to reduce appetite. Tirzepatide activates both GLP-1 and GIP receptors, while Semaglutide targets GLP-1 only, to encourage the body to slow down digestion and feel fuller for longer.
Through the Tier 3 NHS weight management services, the weight loss drug Saxenda is also available under specialist prescription and provision.
Contraceptive risk
Recent reports have revealed there is a higher risk of pregnancy when using weight loss drugs in conjunction with the contraceptive pill.
When using Saxenda, Wegovy and Mounjaro, reports have highlighted the weight loss drug reducing the effectiveness of the contraceptive pill. Research has suggested the risk is due to the drug affecting the body's ability to absorb the pill as the drug targets GLP-1.
Many doctors suggest that a non-oral contraceptive should be taken alongside the weight loss drug to ensure the impact of the contraceptive takes place.
Pregnant women
Concerns towards the safety of pregnant women taking medications have heightened since the harmful effects of sodium valproate towards pregnant women and their children have come to light in the last few years.
At this time, there has not been enough research provided on what risks the weight loss drugs may have for women who are pregnant, trying to get pregnant or are currently breastfeeding. Many doctors and the MHRA advise the weight loss drug must not be prescribed to patients of these criteria in consideration of these risks.
Pancreatitis
In June 2025, there was an increase in reports of acute pancreatis in patients using weight loss drugs, linking to GLP-1 medicines.
Since then, the MHRA have invited patients to take part in the Yellow Card Biobank study to understand any genetic links that may contribute to increased risk of acute pancreatitis and other side effects.
Common side effects
Due to the drugs’ impact on the digestive system, some common side effects associated with the weight loss drugs include nausea, vomiting, constipation, diarrhoea and low blood pressure.
However, both doctors and patients have reported that the drugs’ side effects are manageable, lessening over the time of the treatment. Although, some decided to stop the treatment plan due to these effects.
The risk of fakes
Since January 2023, the Medicines and Healthcare products Regulatory Agency (MHRA) has warned the presence of counterfeit and harmful Ozemptic or Saxenda pens in the UK. These pens were obtained through non-legitimate routes, without healthcare approval. Without legitimate safety standards, the drug can provide a significant risk to health.
The agency urges the weight loss drug should only be obtained through a correct diagnosis and prescription.
Lara Bennett, senior associate in the clinical negligence team, advises: "Weight loss injections work very well for some people - but they carry a raft of side effects and potential complications which are of course not advertised in social media marketing, and people risk seeing only the benefits while remaining oblivious to the very real risks.
“If you are starting or consider this form of treatment, your doctor or other healthcare provider must be clear about any potential side effects and make any necessary provisions over the course of your treatment. Never seek such medication from anywhere but a reputable source and on prescription.
“Following diagnosis, ask plenty of questions to your doctor and carry out necessary research so you can understand if this course of treatment feels right for you. Your healthcare provider has a duty to ensure that your treatment is as effective as possible; therefore, if you feel concern at any time of the treatment, be sure to speak up about your concerns to determine what the next suitable steps might be – even if you aren’t sure.”
If you have a medical negligence claim
Our team are here to help you. If you believe you or a loved one have suffered medical negligence by a healthcare provider, call us today on 0330 041 5869 or contact us online today for help with your claim.
