Different antidepressant drugs are currently used for the treatment of depression in cancer patients, such as second-generation antidepressants and, recently, the extracts of Hypericum perforatum. These agents are susceptible to metabolically-based drug interactions with anticancer drugs. The aim of the present article is to provide an updated review of clinically relevant metabolic drug interactions between selected anticancer drugs and antidepressants, focusing on selective serotonin reuptake inhibitors (SSRIs) and Hypericum extract. SSRIs can cause pharmacokinetic interactions through their in vitro ability to inhibit one or more cytochrome P450 isoenzymes (CYPs). SSRIs differ in their potential for metabolic drug interactions with anticancer drugs. Fluoxetine and paroxetine are potent inhibitors of CYP2D6 and administration of these SSRIs reduces the clinical benefit of an anticancer drug, such as tamoxifen, by decreasing the formation of active metabolites of this drug. Women with breast cancer who receive paroxetine in combination with tamoxifen are at increased risk for death. Other SSRIs, including citalopram, escitalopram, are weak or negligible inhibitors of CYP2D6 and are less likely to interact with anticancer drugs, while sertraline causes significant inhibition of this isoform only at high doses. Hypericum extract, by inducing both the CYP3A4 and the P-glycoprotein (P-gp), can reduce the plasma concentrations of different antineoplastic agents such as imatinib, irinotecan and docetaxel, thus reducing the clinical efficacy of these drugs. Although these interactions are often predictable, the use of fluoxetine, paroxetine and Hypericum extract should be avoided in cancer patients.