There is not enough evidence to safely recommend popular weight loss injections to cancer patients without a specialist prescription, a leading cancer charity has warned.
Macmillan Cancer Support reported a sharp increase in enquiries about so-called “skinny jabs” and urged people to speak to their doctors before using any unprescribed medication.
“While ‘quick fixes’ may seem attractive, we simply do not know enough about the long-term impact of these weight loss medications to recommend them if they’re not prescribed by a specialist,” said Dr. Owen Carter, national clinical adviser at Macmillan.
The charity warned that more research is needed, and weight loss drugs may affect how other medications are absorbed by the body, including some anti-cancer drugs.
Macmillan urged caution among patients with a history of thyroid cancer, pointing to animal studies linking the drugs to thyroid tumours. While this link hasn’t been confirmed in humans, it remains a subject of ongoing research.
Some patients are seeking to lose weight before surgery or treatment to improve outcomes.
“It is understandable that lots of people are interested in new drugs which accelerate weight loss, particularly if they want to manage their weight before or after treatment for cancer,” said Carter.
Impact on Contraception
The guidance follows a recent alert by the Medicines and Healthcare products Regulatory Agency (MHRA), which highlighted that weight loss injections may interfere with the effectiveness of hormonal contraception.Patients are advised to use reliable forms of contraception while taking these medications, and in some cases to continue doing so for up to two months after stopping treatment before attempting to conceive.
These medications should not be used during pregnancy, while trying to become pregnant, or while breastfeeding.
Concerns Over Unsafe Access
Weight loss drugs such as Ozempic, Wegovy, and Mounjaro are available via the NHS, but access is limited.Ozempic, primarily licensed for type 2 diabetes, isn’t offered on the NHS for weight loss.
Wegovy (semaglutide) became available on the NHS in September 2023, but only to adults with obesity or significant weight-related health problems, and only through specialist weight management services after a GP referral.
The rollout of Mounjaro (tirzepatide) is being phased in, with eligibility initially limited to those with a high BMI and multiple obesity-related conditions, and prescriptions restricted to specialist-led services, not GPs
Patients must also participate in structured lifestyle support alongside any prescription.
With NHS access limited, some people are turning to local pharmacists or unregulated online sellers to get hold of weight loss drugs.
Obesity’s Role in Cancer
In the UK, cancer remains a major health challenge. In 2021, there were 168,873 cancer-related deaths—roughly 460 per day—with lung, bowel, breast, and prostate cancers together accounting for almost half (45 percent) of all cancer deaths in 2017–2019.Meanwhile, obesity and being overweight have become the nation’s second-largest preventable cause of cancer after smoking, responsible for causing 6 percent of cases.
After four years, patients using GLP-1 medications had a 7 percent lower risk of developing 14 types of obesity-related cancer, and an 8 percent lower risk of dying from any cause, compared to those taking a different kind of medication.
The biggest benefits were seen in bowel cancers, with 16 percent fewer colon cancer cases and 28 percent fewer rectal cancer cases.
Effective weight management in both cancer prevention and ongoing care is crucial, but health experts warn that weight loss injections should not be viewed as a first-line solution.
Instead, they should be used in conjunction with sustainable lifestyle changes—such as improving diet and increasing physical activity—to support long-term results and reduce the likelihood of regaining weight once medication is discontinued.
