Mycophenolic acid is an immunosuppressant medication used to prevent rejection following organ transplantation and to treat autoimmune conditions such as Crohn's disease and lupus.

[13] Other serious side effects include an increased risk of cancer, progressive multifocal leukoencephalopathy, anemia, and gastrointestinal bleeding.

Mycophenolate sodium has also been used for the prevention of rejection in liver, heart, or lung transplants in children older than two years.

[12] Further work addressing maintenance therapy demonstrated mycophenolate superior to cyclophosphamide, again in terms of response and side-effects.

[12][23] Walsh proposed that mycophenolate should be considered as a first-line induction therapy for treatment of lupus nephritis in people without kidney dysfunction.

[24] Compared with azathioprine it has higher incidence of diarrhea, and no difference in risk of any of the other side effects in transplant patients.

Infrequent adverse effects (0.1–1% of people) include esophagitis, gastritis, gastrointestinal tract hemorrhage, and/or invasive cytomegalovirus (CMV) infection.

[2][33] Purines (including the nucleosides guanosine and adenosine) can either be synthesized de novo using ribose 5-phosphate or they can be salvaged from free nucleotides.

Mycophenolic acid is a potent, reversible, non-competitive inhibitor of inosine-5′-monophosphate dehydrogenase (IMPDH), an enzyme essential to the de novo synthesis of guanosine-5'-monophosphate (GMP) from inosine-5'-monophosphate (IMP).

[40] It is usually used as part of a three-compound regimen of immunosuppressants, also including a calcineurin inhibitor (ciclosporin or tacrolimus) and a glucocorticoid (e.g. dexamethasone or prednisone).

[44] Although it is not commercialised as antibiotic due to its adverse effects, its modified compound (ester derivative) is an approved immunosuppressant drug in kidney, heart, and liver transplantations, and is marketed under the brands CellCept (mycophenolate mofetil by Roche) and Myfortic (mycophenolate sodium by Novartis).

He conceived an idea that if a molecule that could block the enzyme is discovered, then, it would become an immunosuppressive drug that could be used for autoimmune diseases and in organ transplantation.

In one of their experiments the Allisons used an antibacterial compound, mycophenolate mofetil, which was abandoned in clinical use due to its adverse effects.

[54][55] After successful clinical trials,[56] the compound was approved for use in kidney transplant by the U.S. Food and Drug Administration on 3 May 1995,[57] and was sold under the brand name CellCept.

[10] Professor CHAN Tak Mao, Daniel from the University of Hong Kong was the first to champion the use of mycophenolate in lupus nephritis, which has since become standard-of-care internationally.

[60] It was initially introduced as the prodrug mycophenolate mofetil (MMF, trade name CellCept) to improve oral bioavailability.

[citation needed] A combination of mycophenolate and ribavirin has been found to stop infection by and replication of dengue virus in vitro.