Drugs often exist as chiral molecules, which means they have non-superimposable mirror images. The two mirror images, or enantiomers, can interact differently with biological systems. For example, the drug thalidomide exists in two enantiomeric forms: one form is effective as a sedative, while the other caused severe birth defects. This tragic example highlights the need for careful consideration of stereochemistry in drug development and safety evaluation.
