Wanting to start alli program but wonder if taking a diet pill will affect the efficiency of birth control?

I have looked into that and largely diet pills do not have an effect on birth control, but you may want to check next to a doctor just to be sure. And to be extra risk-free you could use a back-up method of birth control, such as a condom. Good luck.
Read the directions on the box or since your already on the internet research it to see if it is safe.