Necon 1/35 - will azithromycin [Zpack] make my pill less effective [1/35] and if so, for how long?

There is an interaction that suggests that the effectiveness of estrogen-containing oral contraceptives such as Necon 1/35 may be impaired by antimicrobial agents such as azithromycin.

The risk appears to be small, but to be on the safe side it is recommended that alternative or additional methods of birth control should be considered during and for at least one week beyond the last dose of antimicrobial therapy.

You can check drug interactions at http://www.drugs.com/drug_interactions.html