"i took amoxicillin thursday feb. 2nd. I am on birth control. I wanted to know how long it takes for birth control to have its full affect again.

I. I have been advised of two different standards. The first is to use back up birth control (i.e., barrier method) for the full duration that you are on antibiotics. The second is to use back up birthcontrol or abstain for the full period you are on antibiotics plus an additional seven days.
The. The only antibiotic ever shown to definitely affect the effectiveness of bcp's is rifampin, which is rarely used today. If you're concerned use a barrier method while on the antibiotic, such as a condom. If you're taking your birth control pills a directed you likely have nothing to be concerned about.