A few days ago I took my younger sister to the doc to start birth control pills. She needed to be on it as there are no need for unplanned teen pregnancies. We both know it's very bad to smoke while using birth control, but she asked me if smoking weed would have any decrease in efficiancy or cause any issues while on the pill. I couldn't answer her question, that's why I'm asking on here. I try to give her the best advice possible that she needs to not be smoking weed and drinking. But there's not much I can do, shed do it behind my back anyway and there wouldn't be a way for me to know as she is not under my care. Any advice ?

It lowers results.

** and often causes forgotten pills, more sexual encounters, which increase odds.