Overview
- The NHS says tirzepatide (Mounjaro) can reduce the effectiveness of oral contraceptives and HRT by slowing gastric emptying, advising backup contraception during sickness and noting non-oral methods are unaffected.
- For semaglutide (Wegovy/Ozempic), the NHS reports no direct reduction in pill efficacy, though vomiting or diarrhoea may still impair absorption and GLP‑1 drugs must be stopped before conception.
- A University of Oxford review of 37 trials found users regain much of the lost weight within roughly 20 months after stopping, with metabolic gains trending back toward baseline in about 1.4 years.
- Deakin University research warns rapid, drug-driven weight loss without resistance training can cause loss of muscle mass, strength and bone density, with AUSactive urging structured strength and weight-bearing exercise.
- Regulators highlight common gastrointestinal side effects—nausea, vomiting and diarrhoea—with some severe cases reported, and the MHRA cautions against buying the jabs from unregulated online sellers.