Carmustine causes cross-links in DNA and RNA, leading to the inhibition of DNA synthesis, RNA production and RNA translation (protein synthesis). Carmustine also binds to and modifies (carbamoylates) glutathione reductase. This leads to cell death.

Carmustine is one of the nitrosoureas indicated as palliative therapy as a single agent or in established combination therapy with other approved chemotherapeutic agents in treatment of brain tumors, multiple myeloma, Hodgkin's disease, and non-Hodgkin's lymphomas. Although it is generally agreed that carmustine alkylates DNA and RNA, it is not cross resistant with other alkylators. As with other nitrosoureas, it may also inhibit several key enzymatic processes by carbamoylation of amino acids in proteins.

Hepatic and rapid with active metabolites. Metabolites may persist in the plasma for several days.

The oral LD₅₀s in rat and mouse are 20 mg/kg and 45 mg/kg, respectively. Side effects include leukopenia, thrombocytopenia, nausea. Toxic effects include pulmonary fibrosis (20-0%) and bone marrow toxicity.