Depression is common during pregnancy, and a considerable proportion of pregnant women take antidepressants. Modern antidepressants (e.g. SSRIs) are fairly safe to use during pregnancy. Several physiological changes occur in the pregnant state, possibly affecting the pharmacokinetics of many drugs. Metabolism via CYP enzymes are important for the elimination of antidepressants. This metabolism may increase, decrease or remain constant throughout pregnancy. The activity of CYP2D6 increases drastically with pregnancy progression, causing decreasing serum concentrations of drugs metabolised via this enzyme. Examples of such drugs are paroxetine and fluoxetine. The field of pregnancy-related pharmacokinetics of antidepressants is still in its early stages. More research will be necessary in the future, to enable evidence-based clinical decisions and optimise antidepressant treatment for pregnant women.