Immunosuppressant drugs are a class of drugs that suppress, or reduce, the strength of the body’s immune system. Some of these drugs are used to make the body less likely to reject a transplanted organ, such as a liver, heart, or kidney. This chapter covers the azathioprine along with their indication, dose, contraindication, precaution, adverse effect, and drug interaction. Renal transplant rejection, adjunct, prophylaxis, rheumatoid arthritis, and autoimmune diseases are the indications of azathioprine. Hypersensitivity, previous treatment with alkylating agents, pregnancy, and lactation are the contraindications of azathioprine.