A clinical trial allows researchers to compare the effects of different treatments, ensuring that drugs are safe and effective before being marketed. They are split into different phases which each test for specific things. If a medicine passes these phases, it can be giving a marketing licence, which makes it available on prescription, (though the side effects and effectiveness of the drug are still monitored while it is being used). In theory, these trials should be diverse, so that many different people can effectively benefit from the drug’s use, and for researchers to know how medicines affect these different groups of people. But clinical trials are still failing to sufficiently represent one of the largest groups on the planet: women.