Methotrexate: what it does and what to watch
Also known as: DMARD, Antifolate · Disease-modifying antirheumatic drug (DMARD) and antifolate agent · Updated 2026-08-19 · Educational — not medical advice
In plain language: This medicine blocks an enzyme the body needs to recycle folate, a vitamin essential for making new DNA, which slows down cells that divide quickly, including the overactive immune cells driving autoimmune inflammation. At the low weekly doses used for arthritis and psoriasis, the main benefit comes from this immune-calming, anti-inflammatory effect rather than from killing cells outright the way much higher cancer-treatment doses do. Because folate is also needed by many normal, healthy cells, a folic acid supplement is typically prescribed alongside it to protect those cells while leaving the anti-inflammatory effect largely intact.
What it's used for
- Rheumatoid arthritis and certain other autoimmune joint and skin conditions
- Psoriasis that hasn't responded to milder treatments
- Certain cancers, at very different doses and monitoring intensity than autoimmune use
Common side effects
- Nausea or stomach upset
- Fatigue, sometimes concentrated on the day after taking it
- Mouth sores
- Hair thinning
- Headache
- Mild hair or skin changes
Get medical help if…
Unusual bruising, bleeding, unexplained fever, or sore throat, which can point to a serious drop in blood cell counts
Persistent cough or shortness of breath, which can signal a rare but serious lung reaction
Yellowing of the skin or eyes, or persistent nausea, which can point to liver involvement, especially with cumulative long-term use
Signs of kidney problems, such as a marked reduction in urination, since reduced kidney clearance can raise this medicine to toxic levels
Lab values it can move
Few guides tell you this part: medicines show up in blood work. If you take Methotrexate and a value below looks off on your report, this may be part of the story — never stop a medicine without your doctor.
White blood cell counts are checked regularly, since this medicine can suppress bone marrow production, and a low count raises infection risk.
WBC / Total Leukocyte CountPlatelet counts are monitored alongside white cells, since bone marrow suppression can affect all blood cell lines together.
Platelet CountLiver enzymes are checked on a regular schedule, since this medicine can cause liver inflammation that builds up with cumulative exposure over months to years.
SGPT (ALT)Kidney function is checked before starting and periodically afterward, since reduced clearance allows the medicine to build up to toxic levels in the blood.
CreatinineGood to know
- This is prescribed once weekly, not daily; taking it every day by mistake is a well-documented, life-threatening dosing error, and any confusion about the schedule should be clarified with a prescriber or pharmacist before taking a single extra dose
- A folic acid supplement is typically prescribed alongside this medicine to reduce certain side effects, and taking it as directed is part of the overall safety plan
- This medicine is absolutely avoided during pregnancy because of a well-established risk of serious birth defects and pregnancy loss, and reliable contraception is discussed for anyone who could become pregnant, for both the person taking it and, in some cases, their partner
- Regular blood count, liver, and kidney monitoring is scheduled at intervals set by the prescriber and should not be skipped, since problems often show up on labs before symptoms appear
- Alcohol is generally minimized or avoided, since it adds to the strain this medicine already places on the liver
Questions people ask
Why is the once-weekly schedule for this medicine so important?
For autoimmune and inflammatory conditions, this medicine is deliberately prescribed as a single weekly dose, not a daily one, because daily dosing at the same tablet strengths delivers a cumulative amount far beyond what the body can safely process. Mistaking it for a daily medicine is a well-documented, life-threatening error, which is why any uncertainty about the schedule deserves an immediate call before taking another dose.
Why is a folic acid supplement given alongside this medicine?
This medicine works partly by blocking how the body uses folate, which is also needed by many ordinary, healthy cells like those lining the mouth and gut. A folic acid supplement, taken on a separate schedule from the methotrexate itself, helps protect those normal cells and reduce side effects like mouth sores and nausea, without meaningfully undoing the anti-inflammatory benefit the medicine provides for arthritis or psoriasis.
Why is pregnancy avoidance treated as absolute with this medicine?
This medicine interferes directly with the rapid cell division that a developing pregnancy depends on, and it's strongly linked to serious birth defects and pregnancy loss when taken during pregnancy. Because of this well-established risk, it's considered an absolute contraindication in pregnancy, reliable contraception is discussed before starting, and the medicine is typically stopped well in advance of any planned pregnancy, under a prescriber's specific guidance.
Taking Methotrexate? See what your blood work says.
Upload your lab report — every value checked and explained. Free — no account needed.