Hi!
USUALLY contractions cause dilation. That is most commonly the way it works, although some people can dilate without contractions, and others won't dilate even with the strongest contractions. The nifedical should slow down the contractions, or at least make them milder. It may give you headaches or make you retain water. Depending on how far along you are though, it could be pretty important to keep them stopped, so follow your doctor's good advice. Congratulations in advance.