 [ Symptoms ] i had a motor nerve conduction study that according to my doctor is clean need second opinion [ Disease ] viagra is not known to cause late or missed periods your period could be late for many reasons including stress and psychological status… no need to worry as viagra usually causes vasodilatation so it is supposed to help period pains and increase blood flow… wait and relax your period may come a bit late if not…try a blood pregnancy test after a while … follow up with me so i can help you as possible