For most doctors prescribing a drug to a pregnant woman is like taking a journey through uncharted territory; navigation is made no easier by the darkness cast by “thalidomide's long shadow.”1 The usual benchmarks are absent because evidence from large clinical trials doesn't exist for drug treatment during pregnancy. Information on many drugs includes non-specific warnings along the lines of “not to be used in pregnancy unless the benefits outweigh the risks,” even though the benefits may not have been confirmed and the risks are not specified. Also, the disease being treated may affect or be affected by pregnancy. Nevertheless, at least a third of all pregnant women in the United Kingdom are prescribed at least one course of drug treatment.2 The purpose of this review is to summarise some of the important points that should be considered when prescribing drugs for pregnant women.