I am on 150mg topirmate wondering if it will effect my birth control nexplanon?

Topiramate can lower the effects of nexplanon. See your doctor

Topiramate , like some other anticonvulsants , can reduce the level of hormones in certain birth control medications , including nexplanon. According to the manufacturer, less than 200 mg of topiramate may not decrease the efficacy of nexplanon, but often the physician will advise another form of contraception for patients on topiramate , because of the risk of birth defects if pregnancy occurs.