No, the antiviral drug Valtrex (valacyclovir) should not make birth control less effective.

Valtrex treats herpes virus infections, such as herpes zoster (shingles) and genital herpes simplex. I could not find any reports of drug interactions with hormone-based medications used for birth control. This includes oral contraceptives, the patch, the ring, skin implants or injections.

In fact, Valtrex has no significant drug-drug interactions.

You may have heard an older concern that oral antibiotics might decrease the effectiveness of birth control pills and increase the risk of unwanted pregnancy. More recent studies do not support this conclusion. If a woman takes her birth control pills as prescribed, taking an antibiotic such ampicillin and tetracycline should almost never be a problem. However, many doctors, including myself, recommend backup birth control during that cycle. Since this is a short-term issue, condoms are usually the most convenient backup method.