A chemotherapy drug that became a cornerstone of modern autoimmune disease treatment

Health · Published 3 October 2026 · Updated 25 October 2026 Swipe more like this →

In short: Originally developed in 1947 to fight cancer, methotrexate has evolved into a versatile, essential medicine. While it remains a potent chemotherapy agent, its ability to suppress the immune system makes it a first-line therapy for conditions like rheumatoid arthritis, proving that a drug's purpose can shift dramatically over time.

Methotrexate, originally known as amethopterin, was born from the discovery that folic acid could worsen leukemia. Researchers realized that folic acid deficiency might actually improve the condition, leading to the development of folic acid analogues. By 1956, methotrexate had replaced its predecessor, aminopterin, due to a superior therapeutic index. It achieved the first cures of metastatic cancer that same year, thanks to the work of Min Chiu Li and his collaborators, who demonstrated complete remission in choriocarcinoma.

The drug's mechanism depends on the condition being treated. In cancer, it acts as an antimetabolite, competitively inhibiting the enzyme dihydrofolate reductase. This blocks the synthesis of DNA and RNA, effectively stopping rapidly dividing cancer cells. However, in autoimmune diseases like rheumatoid arthritis, the mechanism is more complex. It is thought to involve the accumulation of adenosine, the inhibition of T-cell activation, and the down-regulation of B-cells, rather than simple folate inhibition.

Despite its utility, methotrexate requires careful management. Because it is teratogenic, it must be avoided during pregnancy and breastfeeding. Patients often take it weekly rather than daily to limit toxicity, and regular monitoring of blood counts and liver function is standard. It also interacts with numerous common medications, including NSAIDs and certain antibiotics like trimethoprim, which can lead to life-threatening organ toxicity. Today, it remains on the World Health Organization's List of Essential Medicines, with over 4 million prescriptions filled in the United States in 2023 alone.

The drug's impact on autoimmune disease is profound. For rheumatoid arthritis, it can slow or stop disease progression, with some patients seeing the process completely halted. While it can cause side effects like nausea or fatigue, it is generally well-tolerated at the lower doses used for chronic conditions. Ongoing research continues to explore its role in combination therapies, such as pairing it with biologics to improve efficacy in early-stage rheumatoid arthritis and ulcerative colitis.

General information, not professional advice. Spotted an error? Flag the card or see corrections and complaints.

Intellect Plus is a visual educational discovery platform for exploring fascinating facts and ideas. Brain Food, Not Brain Rot. What is Intellect Plus?

Related

• The gold standard for arthritis is an antimetabolite with many faces
• A potent cancer drug discovered in the lab is also found in nature.
• A Croatian antibiotic that lingers in tissue for days
• How a specific enzyme block prevents your body from attacking itself
• Why a potent cancer drug discovered in Italian soil earned the name Red Devil.
• How a common heart medication works by blocking your body's stress signals
• Once a celebrated insomnia cure, this sedative became a symbol of 1970s excess.
• How a simple antibiotic turns into a DNA-shredding weapon inside your body
• Is this century-old diabetes medication the most versatile drug in modern medicine?
• Beyond the delivery room: why the midwife is the ultimate expert on maternal health
• Was Rome's most notorious empress a political victim or a genuine monster of depravity?
• A throbbing neurology problem shadows one in seven people

More in Health, medicine and disease · More in Health · Latest · A–Z · All topics