6-MP, also known as mercaptopurine, is a chemotherapy medication that belongs to the class of purine antagonists. It has been used for many decades in the treatment of certain cancers, particularly blood-related cancers. It is also used to manage some autoimmune and inflammatory diseases. Mercaptopurine is usually taken orally and is often part of long-term maintenance therapy. It works by targeting rapidly dividing cells, which is a common characteristic of cancer cells and certain immune responses.

Mechanism of Action
Mercaptopurine is a prodrug that is converted in the body into active metabolites which inhibit purine synthesis. Purines are essential components of DNA and RNA. By disrupting purine production, mercaptopurine interferes with the growth and replication of cells, especially those that divide quickly, such as leukemic cells. This leads to a reduction in abnormal white blood cell production, which is the hallmark of many types of leukemia and lymphomas.

Uses
6-MP is primarily used in the treatment of acute lymphoblastic leukemia, particularly during the maintenance phase of therapy. It may also be used in other types of leukemia or lymphomas as part of combination chemotherapy regimens. Additionally, mercaptopurine is sometimes prescribed in low doses to help control autoimmune conditions such as inflammatory bowel disease, including Crohn’s disease and ulcerative colitis, where immune suppression is beneficial.

Adverse Effects
Like many chemotherapy drugs, mercaptopurine can cause a range of side effects. The most common include fatigue, nausea, loss of appetite, and lowered blood cell counts, which can increase the risk of infections, anemia, or bleeding. Liver function can also be affected, so regular blood tests are often necessary to monitor for any signs of liver damage. Some individuals may experience increased sensitivity if they have genetic variations that affect how the drug is metabolised. Rare but serious effects can include pancreatitis or severe myelosuppression. Patients are advised to follow prescribed doses carefully and stay in close communication with their healthcare team.