7-hydroxy Methotrexate is primarily used in medical research and clinical settings to study the metabolism and pharmacokinetics of methotrexate, a widely used chemotherapy agent and immunosuppressant. It serves as a key metabolite in understanding how methotrexate is processed in the body, particularly in patients undergoing treatment for cancers like leukemia, lymphoma, and certain autoimmune diseases such as rheumatoid arthritis. Monitoring its levels helps assess patient response, optimize dosing, and minimize toxicity. Additionally, it plays a role in developing analytical methods for drug monitoring and in studies exploring drug interactions and resistance mechanisms in cancer therapy.