If i took a plan b and then about an hour later smoked weed does it lower the effectiveness of the plan b?

While marijuana does not interfere with female hormones (the active ingredient in Plan B), it does lower your immune response to STD's and can increase sexual risk taking behavior.

Agree with Dr. K. weed may not affect plan B, however - Marijuana is a psychoactive drug and will mess with your brain and damage your lungs among other injury. MJ users are called stoners for good reason. Quit using it while you are ahead. Wish you good health!