There is a theory that low serotonin levels caused by lack of oestrogen cause migraines. Low serotonin levels cause all sorts of problems like depression for example and I know from personal experience that I feel much better when taking fairly high levels of oestrogen. If I let my oestrogen levels fall too low, I get silent migraines (migraine aura without headache) but this only happens when I take synthetic progestins which suppress the oestrogen levels. It would not surprise me to find out that low serotonin causes any number of issues, it seems to be an important chemical in the brain. A well known medic who I will not name thinks that too many women are prescribed ADs when they should be on HRT.