Methotrexate — Arthritis & Autoimmune Guide | KiwiMeds
✅ Reviewed by a Registered Pharmacist NZ | Last updated: May 2026 | This information is for educational purposes only and does not replace advice from your doctor or pharmacist.
What is methotrexate?
Methotrexate is a disease-modifying antirheumatic drug (DMARD) used to treat rheumatoid arthritis, psoriasis, and other autoimmune conditions. At the low doses used for arthritis (typically 7.5–25mg weekly), it is quite different from the high doses used in cancer treatment. It is one of the most commonly prescribed DMARDs in New Zealand.
What is it used for? (NZ context)
In New Zealand, methotrexate is widely prescribed for rheumatoid arthritis, psoriatic arthritis, and psoriasis. It reduces inflammation and joint damage. It takes 6–12 weeks to see full benefit. Pharmac funds methotrexate tablets.
How does it work?
At low doses for arthritis, methotrexate modifies immune system function, reducing the inflammatory processes that attack joints. It inhibits the enzyme dihydrofolate reductase, affecting rapidly dividing immune cells. Folic acid is always given alongside methotrexate to reduce side effects.
How to take it
IMPORTANT: Methotrexate for arthritis is taken ONCE A WEEK, not daily. Taking it daily is dangerous and has caused deaths. Take it on the same day each week (e.g., every Monday). Always take folic acid on the other days as prescribed. Never take two doses to make up for a missed dose.
Common side effects
- Nausea — most common, reduced by taking in the evening or with food
- Fatigue
- Mouth sores
- Temporary hair thinning
Serious side effects to watch for
Methotrexate can affect the liver (regular liver function tests are required) and bone marrow (blood tests required). Rarely, it can cause lung inflammation (methotrexate pneumonitis) — report new breathlessness immediately. Never take methotrexate during pregnancy — it causes serious birth defects. Use reliable contraception.
Important drug interactions
NSAIDs (ibuprofen, naproxen) — increase methotrexate toxicity and should be used cautiously. Trimethoprim (in co-trimoxazole antibiotics) — severe interaction, can cause methotrexate toxicity. Folic acid (folinic acid, leucovorin) — given to reduce side effects. Alcohol — increases liver damage risk; minimise or avoid.
NZ-specific information
Pharmac funding: Methotrexate 2.5mg tablets are funded by Pharmac for approved indications. For rheumatoid arthritis, a Special Authority application may be required depending on the specific funding criteria at the time of prescribing.
Frequently asked questions
Is methotrexate a chemotherapy drug?
Methotrexate is used in chemotherapy at high doses, but the weekly low doses prescribed for arthritis and skin conditions are fundamentally different. At these doses it works as an immune modifier rather than killing cancer cells. The dose and safety profile are very different.
Why do I take folic acid with methotrexate?
Methotrexate partially blocks folate metabolism. Taking folic acid on the days you do not take methotrexate reduces side effects like nausea and mouth sores without reducing methotrexate’s effectiveness against arthritis.
What monitoring do I need on methotrexate?
Regular blood tests (full blood count, liver function, kidney function) are required — usually monthly when starting, then every 3 months once stable. Your doctor will also ask about breathlessness at each visit.
💬 Talk to your pharmacist or doctor for personalised advice about methotrexate.
Reviewed by a Registered Pharmacist NZ | BPharm, Pharmacy Council of New Zealand
References & Further Information
The following New Zealand and international resources were used to inform this page: