What happens when you take methotrexate with folate?
Methotrexate is a folate antagonist. Inside cells, it blocks an enzyme called dihydrofolate reductase, which is required to recycle inactive folate back into the active tetrahydrofolate form needed for DNA synthesis and amino acid metabolism. By depleting active folate, methotrexate slows the proliferation of rapidly dividing cells, which is the basis of its use in autoimmune disease (rheumatoid arthritis, psoriasis, psoriatic arthritis, juvenile idiopathic arthritis, inflammatory bowel disease) and in cancer chemotherapy.
The downside of folate depletion is that it produces predictable side effects in normal tissues that depend on folate for cell turnover. Patients commonly experience nausea, vomiting, diarrhea, mouth sores, hair thinning, and elevated liver enzymes. Bone marrow suppression and macrocytic anemia can also occur, particularly with higher doses or kidney dysfunction.
Folic acid supplementation replenishes folate stores in normal tissues. Because the rheumatologic doses of methotrexate (usually 7.5-25 mg once weekly) are far lower than the cancer doses, supplementing folate at the doses used in autoimmune practice does not bypass enough of the methotrexate blockade to compromise efficacy. The Cochrane review of folic and folinic acid in rheumatoid arthritis found a 26% relative risk reduction in GI side effects and a 77% relative risk reduction in transaminase elevations without loss of disease control.
Why is this important?
Methotrexate is the anchor drug for rheumatoid arthritis and is used long-term for many other autoimmune conditions. Side effects are the most common reason patients stop the medication, and discontinuation often means losing disease control and turning to more expensive or higher-risk alternatives. Folate supplementation roughly halves the rate of treatment discontinuation due to side effects in RA, which makes it one of the most cost-effective interventions in rheumatology.
Timing matters. If folic acid is taken on the same day as methotrexate, particularly within a few hours, it can compete with methotrexate for cellular uptake and theoretically reduce efficacy. Most rheumatology guidelines avoid co-administration on the methotrexate day for this reason, even though the practical magnitude of efficacy loss at low folic acid doses is small.
A separate consideration is dose. Standard supplementation in RA is 1 mg daily or 5 mg once weekly. A recent observational analysis suggested that very high doses of folic acid (5 mg daily or more) may be associated with increased cardiovascular events compared with lower doses; this finding is not yet settled but argues against escalating folic acid beyond what is needed to control symptoms.
For cancer chemotherapy, the picture is reversed. High-dose methotrexate regimens for leukemia, lymphoma, osteosarcoma, and other malignancies depend on full folate antagonism for efficacy. Routine folic acid supplementation would compromise the treatment. Instead, leucovorin (folinic acid) rescue is given on a strict schedule after the methotrexate infusion to limit toxicity without canceling the therapeutic effect.
What should you do?
If you take methotrexate for an autoimmune condition, talk to your prescriber about folic acid supplementation if you are not already on it. The most common regimens are folic acid 1 mg daily (skipped on the methotrexate day) or folic acid 5 mg once weekly taken 24 to 48 hours after the methotrexate dose. Some clinicians use folinic acid (leucovorin) 2.5-5 mg once weekly for patients who do not tolerate folic acid.
Do not take folic acid on the same day as methotrexate. Spacing the doses by at least 24 hours preserves the methotrexate effect while still providing the protective benefit. If you are on subcutaneous methotrexate, the same rule applies: take folic acid the next day or later.
Do not start folic acid above 1 mg daily without your prescriber's input, and do not exceed 5 mg daily without strong reason. Higher doses may not add benefit and have been associated with cardiovascular concerns in observational data.
If you are receiving methotrexate as cancer chemotherapy, do not start folic acid supplementation on your own. Your oncologist will prescribe leucovorin rescue at the appropriate times. Casual folic acid use could blunt the chemotherapy.
Watch for ingredients in multivitamins. Most prenatal and many general adult multivitamins contain 400-800 mcg of folic acid (less than the supplementation dose), which is generally compatible with weekly methotrexate when taken on non-methotrexate days. Some B-complex products and methylated folate (L-methylfolate) supplements at higher doses may need to be adjusted; ask your prescriber.
Which specific products are affected?
The interaction applies to all methotrexate formulations including Rheumatrex, Trexall, Otrexup, Rasuvo, and generic methotrexate tablets, oral solution, subcutaneous injection, and IV/IM injection. The folate timing rules are the same regardless of how methotrexate is administered.
On the folate side, the interaction concerns folic acid (pteroylmonoglutamic acid, the synthetic form found in supplements and fortified foods), folinic acid (leucovorin, 5-formyl tetrahydrofolate), and L-methylfolate (5-methyltetrahydrofolate, often sold as Deplin or Metafolin). All three can interact with methotrexate, though the timing recommendations and dose ranges differ slightly.
Be aware of folate-fortified foods. In countries that fortify grain products (United States, Canada, much of Latin America), routine dietary intake provides several hundred micrograms daily. This level is compatible with weekly methotrexate and is not generally a concern, but it is reasonable to avoid heavy intake of fortified cereals on the methotrexate day.
The bottom line
Folic acid supplementation reduces methotrexate side effects substantially in autoimmune patients without compromising efficacy at the doses used in rheumatology. The standard regimen is folic acid 1 mg daily (skip the methotrexate day) or 5 mg once weekly 24-48 hours after the methotrexate dose. Do not take folic acid the same day as methotrexate, and do not exceed 5 mg daily without prescriber input. If methotrexate is being used for cancer, do not add folic acid on your own; your oncologist will direct leucovorin rescue.