Hello Helen, thanks for trusting HCM with your worry, Champix has not been describe to cause menstrual abnormalities. However, the fact that its action is central that is at the level of the brain could probably affects menses. Not withstanding, the first cause of delayed or irregular menses is pregnancy. if you had sexual exposure, pregnancy is likely. Then do pregnancy test to confirm. If negative, exercise some patience and stress free. if menses doesnot come for up to three months with negative routine pregnancy tests then consider seeing a doctor. if you have more query, i will be glad to respond best regards Dr Achuo