Migraine is a common disease that affects about 15% of the population, most of whom are women. It generally begins after adolescence but can also affect individuals over the age of 50. It is also a costly disease as it causes major production losses in society. Latest reports states that it costs Swedish society approximately 5 billion SEK each year. In addition, it also causes great suffering for the affected individual and its relatives. 

The pathophysiology behind migraine is that it occurs sudden and rapid contraction of the blood vessels in the brain, which then rapidly dilates again. It also attracts inflammatory cells and releasement of chemical substances that increases the sensitivity in the neurons. This leads to neurologic inflammation and give symptoms such as nausea, hallucinations, tingling or numbness on one side of the body but also ringing in the ears. The reason why people get migraines is not yet fully understood. A leading cause is heredity. People whose parents have migraines have a 70% risk of passing it on, whereas only one parent has it the risk is 45%. Other factors are such as poor sleep habits, stress, certain foods and in women, hormonal changes. 

The disease is divided into to two different subgroups, chronic and episodic. Those with chronic migraines are more likely to be on sick leave as they have a higher number of monthly migraine days (MMD). There are a total of 12 different types of migraine, each with different symptoms, such as with or without aura. Aura is caused by electrical discharges in the brain and produces symptoms as visual disturbances with flickering. It is very important to know which type of migraine that has occurred to proceed the needed treatment, as there are many to choose from. To treat migraine there are a few options. First, some type of beta-blocker is prescribed to adult patients with at least three attacks per month. Patients can also use over the counter medicines such as NSAID to treat the pain. 

 In the four chosen studies that have been studied during this thesis, researchers have investigated the effects of erenumab in the prophylactic treatment of chronic migraine.  Erenumab is a monoclonal antibody that targets calcitonin related proteins, therefore, the proteins cannot bind to their receptors and the actual inflammation and pain that would occur cannot be created. The studies took place in various places, Asia, North America and Europe. Researchers compared a dosage of 70 mg or 140 mg erenumab with placebo. Most of the participants were women, which mimics the real-world statistics. The purpose behind the studies was to see how erenumab can decrease the number of MMD of the patients. 

The results from the four chosen studies showed that treatment with erenumab, both a 70 mg or a 140 mg dosage, will successfully give a decrease in the amount of MMD. Nevertheless, it needs more studies like these as the need is great. There is still no clear evidence of hoe safe erenumab is for pregnant and breastfeeding women, even though women are over representative in the migraine population.