Hello
Thanks for posting your query at DoctorSpring.com
Topiramate does reduce the efficacy of low dose estrogen pills.
Portia is a low dose estrogen pill.
So you should switch over to a higher dosage of estrogen - containing birth control, or use backup methods till you are on Topiramate.
Alternatively, discuss with your doctor regarding a possible alternative medication to Topiramate.
All the best
Please feel free to discuss further.
Regards