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Why can immunosuppressive drugs increase the risk of infection?

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Tuberculosis — disease A doctor examining chest X-rays of patients infected with tuberculosis, which remains one of the world's deadliest diseases.

Immunosuppressive drugs increase the risk of infection because they intentionally reduce the ability of the immune system to defend the body against pathogens.12

The immune system is responsible for protecting the body by identifying and destroying harmful germs, such as bacteria, viruses, fungi, and protozoa. It relies on specialized white blood cells, including phagocytes and lymphocytes, to scout out and eliminate these invaders.3

Many immunosuppressive agents, such as calcineurin inhibitors or antiproliferative drugs, work by inhibiting the activation, signaling, or proliferation of T lymphocytes. By suppressing these critical components of the immune response, the drugs prevent the body from effectively recognizing and neutralizing infectious organisms. Consequently, individuals undergoing this therapy become susceptible to infections, including those caused by opportunistic pathogens that might otherwise be kept in check by a fully functional immune system.421