Category A: This is the list of drugs that are generally considered safe during pregnancy with the possibility of fetal harm being remote, having been tested in women.

Category B: Includes drugs, which have shown no fetal risk in animals but have not been tested in women. Also includes drugs, which have shown an adverse effect in animals but not in women.

Category C: Adverse effects have been seen in animals but the drugs have not been tested on women. Also includes drugs, which have not been tested in animals or in women. These can be used only if the risk to the fetus is justified by its greater benefits.

Category D: There is definite evidence of fetal risk. Their use can be justified only in life threatening situations, or a serious illness in which safer drugs have proved ineffective or unavailable.

Category X: This comprises the list of drugs, which are completely contra-indicated in pregnancy since the risks far outweigh any possible benefits.