My girlfriend started taking diet pills a week ago and she experienced light period 1 day. ultrasound didn't detect abnormalities. shall we be worried?

Diet Pills: "Diet pills" come in many types and dosages. I would need to know more about the medication. That said, some diet pills have hormones in them. Hormones can effect a woman's menstrual cycle. Since she had an ultrasound, I assume she was seen by a doctor. Also, if she hasn't had a pregnancy test, she should. Lastly, if her weight problem is severe, she should try to get help from a nutritionist.