How come you have such powerful cravings when on your period?

Serotonin: Just prior to your period, the levels of a brain hormone called serotonin begin to drop. A stress hormone called cortisol can rise. The changes in these hormones can make you crave fat and carbs. Chocolate, for example, has been shown to raise serotonin levels. Its a subconscious attempt to self-medicate to raise serotonin and drop cortisol levels. Healthy alternates like exercise can help.