What drug's effectiveness is most reduced by methotrexate?

Which drug’s effectiveness drops the most with methotrexate?

Methotrexate can reduce the effectiveness of the antibiotic trimethoprim, because both drugs affect folate metabolism. Using them together increases toxicity risk and can complicate how well each works clinically, which is why clinicians often avoid the combination or monitor closely.

If you’re asking about a different “reduced effectiveness” interaction (for example, with antivirals, anticoagulants, or biologics), tell me which other drug you mean and I can match the interaction to that specific pairing.