Which drugs efficacy is most affected by methotrexate?

Which cancer or autoimmune drugs become less effective when you take methotrexate?

Methotrexate (MTX) can change the effectiveness and toxicity of several medicines because it affects folate pathways and is often used alongside other drugs that also rely on folate metabolism.

What’s most affected: folate-dependent drugs and antifolates

The main drug class most clearly affected by methotrexate involves folate metabolism. MTX is an antifolate, so drugs that depend on folate pathways can have their activity altered (either by functional “overlap” at the same pathway or by folate depletion effects).

Common examples searched in this space include other antifolates (such as pemetrexed or other folate-targeted anticancer drugs), and folate-dependent antimetabolites. In practical terms, this can mean reduced tolerability and, in some regimens, changes in effectiveness or dose feasibility—often leading clinicians to adjust timing and dosing.

Does methotrexate mainly reduce efficacy or increase side effects?

In many real-world interactions, MTX more reliably increases the risk of adverse effects (and forces dose changes) than it directly “cancels” efficacy. Drug choice and schedule often depend on the specific MTX dose (low weekly dosing for inflammatory disease vs higher dosing in some oncology settings), kidney function, and whether the other drug is also an antimetabolite or antifolate.

What should patients ask their clinician about?

Patients typically need to ask:
- whether their other medicine is also an antifolate or antimetabolite
- whether any leucovorin (folinic acid) “rescue” is part of the plan
- whether their MTX schedule should be separated from the other drug
- how kidney function affects MTX and interaction risk

Important gap: which exact drugs are “most affected” depends on the regimen

The question asks for specific drugs whose efficacy is most affected, but that depends on the clinical context (autoimmune MTX vs high-dose MTX in oncology) and the exact drug combination being considered. If you tell me the condition (e.g., rheumatoid arthritis, psoriasis, Crohn’s) and the other medication(s) you’re asking about, I can narrow it to the most relevant interactions.

Source

I don’t have the specific drug-interaction list you’re expecting from the provided materials here. If you share the country/regimen or the other drug names, I can answer precisely.