This Is Your Brain On PMS.
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I seem to get brain fog around my period. Help!

You're not alone: Brain fog—a combination of feeling sluggish and forgetful—is a common symptom of premenstrual syndrome. In a typical cycle, progesterone levels rise in the two weeks leading up to your period; that has been linked to a drop in serotonin, a neurotransmitter that boosts mood and helps keep you sharp.

To beat the brain blahs, monitor your cycle so you know when you'll be most apt to feel dull. On those days, be diligent about writing things down in your day planner, and prioritize shut-eye even more—getting behind in sleep makes things much worse.

Another cause of brain fog is iron deficiency anemia, which can happen when you lose a lot of blood due to heavy periods or a gut problem like a bleeding ulcer. Anemia symptoms can appear to be more severe during your period. Vegetarians are particularly prone because most people get iron from animal products. Your doctor can check your levels with a quick blood test, and if you're anemic, she'll likely prescribe supplements. It's also a good idea to add more iron-rich foods, such as red meat, leafy greens, egg yolks and beans, to your plate.

Health's medical editor, Roshini Rajapaksa, MD, is assistant professor of medicine at the NYU School of Medicine.