I used clen for about two weeks with my first cycle --- I got up to 3 pills, and couldnt take it . I am prone to migraines, and I got the worst one while taking the clen.....lasted about 4 days. Does affect some with killer headaches.....just monitor your dosage and find what will work for you.
My husband took what I couldnt, and loved it. Works for some and not for others. Best of luck.