The organisation that looks after the safety of prescribed medicines and other health devices and equipment in the UK is the Medicines and Healthcare products Regulatory Agency (MHRA, see Useful links). Its main job is to make sure that medicines and medical devices, from painkillers to pacemakers, work properly and are acceptably safe.
No product is completely risk free, so the MHRA uses as much information as it can to ensure that the benefits of medicines to patients justify any possible risks. It assesses results from clinical trials to decide whether or not new medicines should be licensed for use. No medicine or medical device can be used in the UK until the MHRA has given it a licence, which sets out how it should be used, including what health condition it should be used to treat and what dose should be used.
Ultimately, you and your healthcare professional have to weigh up the pros and cons of each medicine when deciding on the most appropriate treatment. The MHRA also keeps watch over the safety of medicines once they are in clinical use and takes action if a problem arises. This may mean alerting health professionals about a potential issue with a medicine and withdrawing a medicine from the market if it becomes apparent that the side effects outweigh the benefits.
The MHRA works closely with the European regulator, the European Medicines Agency (EMEA), which oversees the safety of medicines across Europe. In some cases, the EMEA takes the lead in the process of licensing medicines used in the UK, although the MHRA still has to give its approval before the medicine can be marketed in this country.