During their periods, women felt their worst and reacted their fastest

Flaminia Ronca and colleagues (Neuropsychologia, 2025) had 105 women with regular cycles take a set of online tests twice, 14 days apart. Click the moment two balls collide. Hit the space bar for a smiley face and leave the winking one alone. Spot the mirror image of a 3D shape. During their periods the women reacted about 10 milliseconds faster than in other phases, a hundredth of a second, and made fewer mistakes. Between ovulation and the next period they slowed by about 10 milliseconds and were worse at timing the collision.

Mood and physical symptoms were at their worst during the period itself. A sizeable share of the women felt their symptoms were dragging down their thinking on test day, and their scores didn't bear that out. "How we feel doesn't always reflect how we perform," Ronca says.

Periods don't make anyone smarter: Ronca herself pointed out that this is only about reaction times and the timing of movements. The authors call the work a proof of principle. Cycle phase came from what participants reported, and the researchers were asking about sport, where milliseconds count. These are averages too, and yours may look different. A bad day for the body isn't always a bad day for the mind.