Patient: Drug interactions between phentermine / topiramate and TriNessa. Hello, I have been taking TriNessa Birth control for almost a year now. I’m a HUGE worrier. I usually start my period on my 3rd or 4th sugar pill. I take my pills at the same time everyday. I started taking phentermine yesterday (2nd sugar pill) and I have read on several sites many different things and I’m scared this will lower my BC effectiveness. I’m freaking out because I am on my 3rd sugar pill and have not started my period. I’m terrified. I had relations yesterday before I took my first phentermine. I know stressing and worrying will delay my period but I need to know everything with these two drug interactions. I just want to put my mind at ease. I’m scared I won’t start tomorrow and I know you can miss a period because of less uterine lining but I’m very nervous and stressed. Please help? I’ve had 2 pharmacists advice and they both gave me completely opposite answers. Thank you.
Doctor: Welcome to Ask The Doctor.We are here to help you.Phentermine and Topiramate can cause menstrual irregularities.If the exposure was high risk, and you don’t want to conceive then you can take emergency contraceptive pill within 72 hours of exposure.You have not mentioned her your menstrual period date and date you had sex. So, i am unable to calculate if you were in safe period when you had sex or not.Wait for your periods. If you miss your periods, get urine pregnancy test done at home after 10 days of missing her periods.I would advise you to be cautious next time.I hope it helps.Stay Healthy.