Like oral contraceptives, the anti-estrogens tamoxifen also possesses both cancer-causing and cancer preventive properties. There is consistent evidence that use of tamoxifen increases the risk of endometrial cancer whether given as adjuvant therapy among women with breast cancer or as preventive therapy among women at high risk of breast cancer.

Chemotherapeutic drugs used to treat cancer include drugs that may induce secondary cancer in patients who are cured for their primary cancer. However, the proportion of cancer patients receiving benefit from the use of chemotherapeutic drugs is so high in comparison with those developing secondary cancers that the use of these drugs is endorsed.

Immunosuppressants can also induce cancer. These drugs are typically used for serious conditions, such as organ transplantations, haematological diseases, and immunological conditions, and the benefits of these drugs generally outweigh their carcinogenic effects. However, a decision to prescribe and use drugs that are established, or considered likely, to be carcinogenic is more problematic in circumstances involving non-life-threatening conditions and should be based on a careful risk–benefit evaluation.