Mounjaro works as an appetite suppressant by mimicking a hormone called GLP-1, which makes people feel fuller. It also affects metabolism and helps regulate energy balance.
The most common side effects include nausea, vomiting, bloating, constipation and diarrhoea, while some report hair loss and in rare cases gallbladder and kidney problems and depression.
Rebecca started taking the GLP-1 medication in April 2025 after weighing herself during a skiing holiday.
“I stepped on to measure the boots and the skis,” she said. “And I was the same weight as my husband, so I was like: ‘Right, I’ve got to lose the weight’.”
Rebecca lost more than two stone (12.7kg) in two months, and said the weight-loss revealed a small lump deep in her rib cage.
Scans and biopsies followed, and a week and a half later she was given a diagnosis of oestrogen receptor-positive breast cancer.
About 80 out of every 100 breast cancer cases, external are oestrogen receptor positive, which means the tumour contains receptors sensitive to the hormone, which causes the cancer cells to grow and divide.
“I went from feeling great from losing weight to ‘oh God, I’ve got cancer’,” she said.
“Hearing those three words really does shake you up. It just all felt like a bad dream.”