Weight-loss medications, particularly GLP-1 agonist drugs like Wegovy and Mounjaro, have emerged as powerful tools for weight management, but they frequently come with a challenging and often embarrassing side effect: chronic diarrhoea. Clinical trials indicate that up to 30 percent of patients experience this issue, leading to significant distress and disruption in their daily lives.

Patients' experiences highlight the severity of this problem. Bethany Powley, a 34-year-old mental health nurse using Wegovy, reported developing terrible diarrhoea within 24 hours of her first dose. While the medication led to an impressive 10lb weight loss in a month, the chronic bowel issues caused anxiety about leaving home and impacted her work punctuality. Facing a lack of support from her GP due to sourcing the medication online, Bethany chose to remain on the starter dose and adjusted her diet, avoiding refined sugar, fatty, and greasy foods which she found exacerbated her symptoms.

Online support groups for weight-loss jabs are rife with accounts of urgent bathroom dashes, near-misses, and even public accidents, causing considerable shame and discomfort. Sally Jones, a 69-year-old retired shop assistant on Mounjaro, described experiencing severe, week-long diarrhoea after increasing her dose, which confined her to her home. Despite taking anti-diarrhoea tablets every two hours, they offered little relief, and she suffered dehydration. On one occasion, she had a panicked rush home in the car to reach a toilet in time. Yet, like many, she considers the significant weight loss—four stone to date—a worthwhile trade-off for the side effects.

Samantha Caris, 51, a clerical assistant, also faced crippling diarrhoea after restarting Mounjaro. Her experiences included abruptly leaving a work meeting and having to jump off a bus early to find a public toilet. Despite these distressing incidents, she continues her treatment, prioritizing the weight-loss benefits over the unpleasant side effects.

Dr. Hal Brindley, a consultant gastroenterologist and hepatologist, elucidates the physiological reasons behind this common side effect. GLP-1 agonist drugs function by substantially slowing the stomach's emptying rate, which is beneficial for blood sugar control and promoting satiety. However, these medications can simultaneously accelerate movement in the intestines. This creates a digestive