Tioguanine, also known as thioguanine or 6-thioguanine (6-TG) is a medication used to treat acute myeloid leukemia (AML), acute lymphocytic leukemia (ALL), and chronic myeloid leukemia (CML). Long-term use is not recommended. It is given by mouth.Common side effects include bone marrow suppression, liver problems and inflammation of the mouth. It is recommended that liver enzymes be checked weekly when on the medication. People with a genetic deficiency in thiopurine S-methyltransferase are at higher risk of side effects. Avoiding pregnancy when on the medication is recommended for both males and females. Tioguanine is in the antimetabolite family of medications. It is a purine analogue of guanine and works by disrupting DNA and RNA.Tioguanine was developed between 1949 and 1951. It is on the World Health Organizations List of Essential Medicines. Medical uses
Acute leukemias in both adults and children
Chronic myelogenous leukemia
Inflammatory bowel disease, especially ulcerative colitis
Psoriasis

Side effects
Leukopenia and neutropenia
Thrombocytopenia
Anemia
Anorexia
Nausea and vomiting
Hepatotoxicity: this manifests as:

Hepatic veno-occlusive disease
The major concern that has inhibited the use of thioguanine has been veno-occlusive disease (VOD) and its histological precursor nodular regenerative hyperplasia (NRH). The incidence of NRH with thioguanine was reported  as between 33 and 76%. The risk of ensuing VOD is serious and frequently irreversible so this side effect has been a major concern. However, recent evidence using an animal model for thioguanine-induced NRH/VOD has shown that, contrary to previous assumptions, NRH/VOD is dose dependent and the mechanism for this has been demonstrated.
Functional biliary sphincter of Oddi disorder
If all of the above criteria are met, individuals are classified as having a functional biliary sphincter of Oddi disorder, if the testing of pancreatic enzymes (amylase and lipase) is normal.The old Milwaukee classification of biliary sphincter of Oddi dysfunction (SOD) used to divide the condition into three subtypes: but it is no longer in use. Type I included patients with biliary-type abdominal pain, with all of altered liver enzymes on blood testing, dilated biliary ducts on ultrasound or ERCP, and delayed bile clearance on HIDA scan. Type II included patients with biliary-type abdominal pain associated with at least one of the following: altered liver enzymes on blood testing, dilated biliary ducts on imaging tests, and delayed bile clearance on HIDA scan. Biliary-type pain in the absence of any sign of biliary or pancreatic alteration was the so-called Type III biliary SOD. The hypothesis that this pain could be linked to SOD has been studied in a large trial published in JAMA (2014)  where patients were randomized to sphincterotomy or sham surgery. Contrary to expectations, patients who were not subjected to sphincterotomy fared better. Overall, the investigators found that only 23% of the patients who underwent sphincterotomy  improved versus 37% of the control group. The EPISOD trial has substantiated the ineffectiveness of endoscopic sphincterotomy in patients with these symptoms and SOD Type III is no longer considered to be a clinical entity.