About this information
This NHS content is written for people in England. Medicine names, availability, prescribing and services may differ in other countries.
This NHS entry is an overview page. Its detailed guides are being refreshed.
Content supplied by the NHS website, refreshed 19 August 2026. View the original NHS article ↗
Licensed under the Open Government Licence v3.0 ↗. MyPHU is independent and is not endorsed by the NHS.