Doxorubicin, sold under the brand name Adriamycin among others, is a chemotherapy medication used to treat cancer. This includes breast cancer, bladder cancer, Kaposi's sarcoma, lymphoma, and acute lymphocytic leukemia. It is often used together with other chemotherapy agents. Doxorubicin is given by injection into a vein.

Common side effects include hair loss, bone marrow suppression, vomiting, rash, and inflammation of the mouth. Other serious side effects may include allergic reactions such as anaphylaxis, heart damage, tissue damage at the site of injection, radiation recall, and treatment-related leukemia. People often experience red discoloration of the urine for a few days. Doxorubicin is in the anthracycline and antitumor antibiotic family of medications. It works in part by interfering with the function of DNA.

Doxorubicin was approved for medical use in the United States in 1974. It is on the World Health Organization's List of Essential Medicines. Versions that are pegylated and in liposomes are also available; however, they are more expensive. Doxorubicin was originally made from the bacterium Streptomyces peucetius.

In the EU doxorubicin pegylated liposomal (as Caelyx) is indicated to treat breast cancer, ovarian cancer, and AIDS-related Kaposi's sarcoma. It is indicated to treat multiple myeloma in combination with bortezomib. Doxorubicin hydrochloride (as Myocet liposomal) is indicated to treat breast cancer in combination with cyclophosphamide.

Doxorubicin is commonly used to treat some leukemias and lymphomas, as well as cancers of the bladder, breast, stomach, lung, ovaries, thyroid, soft tissue sarcoma as well as aggressive fibromatosis (desmoid tumor), multiple myeloma, and others. Commonly used doxorubicin-containing regimens are AC (Adriamycin, cyclophosphamide), TAC (taxotere, AC), ABVD (Adriamycin, bleomycin, vinblastine, dacarbazine), BEACOPP, CHOP (cyclophosphamide, hydroxydaunorubicin, vincristine, prednisone) and FAC (5-fluorouracil, adriamycin, cyclophosphamide). Its activity is inhibited by certain antioxidant plant extracts, for example Tragia volubilis aqueous extract.

Doxil (see below) is used primarily for the treatment of ovarian cancer where the disease has progressed or recurred after platinum-based chemotherapy, or for the treatment of AIDS-related Kaposi's sarcoma.

The most dangerous side effect of doxorubicin is dilated cardiomyopathy, leading to congestive heart failure. The rate of cardiomyopathy is dependent on its cumulative dose, with an incidence about 4% when the dose of doxorubicin is 500–550 mg/m², 18% when the dose is 551–600 mg/m² and 36% when the dose exceeds 600 mg/m². There are several ways in which doxorubicin is believed to cause cardiomyopathy, including oxidative stress due to iron accumulation, downregulation of genes for contractile proteins, and p53-mediated apoptosis.

Doxorubicin-induced cardiomyopathy typically results in dilated cardiomyopathy, with all four cardiac chambers being enlarged. This results in both systolic and diastolic dysfunction. Eventually, heart failure can result, which carries a 50% mortality rate. There is no effective treatment against established cardiomyopathy caused by the drug as of 2010. The drug dexrazoxane, which is an iron chelator, may be used to decrease the risk of doxorubicin's cardiotoxicity in certain cases.