Prescription

Four weight loss medications are licensed in the UK: orlistat (NHS Tier 2), liraglutide/Saxenda (NHS Tier 3), semaglutide/Wegovy (NHS Tier 3), and tirzepatide/Mounjaro (NHS Tier 3). Phentermine is not licensed in the UK. This article covers mechanisms, evidence, NHS eligibility, and the private prescribing pathway.

Topiramate is an anticonvulsant and antimigraine drug that causes weight loss as a documented side effect — not as its primary indication. In the UK, topiramate monotherapy for weight loss is not MHRA-licensed. The combination Qsymia (topiramate + phentermine) is licensed in the US but not the UK. Topiramate's weight loss mechanisms: appetite suppression via GABA-A receptor modulation and carbonic anhydrase inhibition, altered taste perception, and possible reduced caloric intake. Side effects include cognitive impairment, paraesthesia, and teratogenicity (Category D — must not be used in pregnancy without contraception).