Its pretty commonly known that modifying hormonal levels gives people migraines sometimes. Women on Estrogen get them frequently.
I religiously got a severe migraine if I would go off of Propecia for any extended period of time (1 week) and then back on it again. Lasted a day or so, or until I had a full nights sleep.
Headaches were the most common side effect I had directly related to the usage of Propecia.
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