Methotrexate 2.5 mg Tablets: Prescription DMARD for Rheumatoid Arthritis and Psoriatic Arthritis — Weekly Dosing, Folic Acid Supplementation

Reviewed by the Lucas Clinic Medical Team | Updated May 2026

Methotrexate is a folate antagonist antimetabolite with a remarkably broad range of clinical applications — spanning oncology, rheumatology, and dermatology. Originally developed as an anticancer agent in the 1940s (when it was known as amethopterin), methotrexate was found in subsequent decades to be effective as a disease-modifying antirheumatic drug (DMARD) at much lower doses than those used in chemotherapy. This lower-dose, typically once-weekly rheumatological regimen is now the most common form of methotrexate use globally — it is the anchor DMARD and first-line treatment for rheumatoid arthritis (RA), psoriatic arthritis, and several other inflammatory conditions.

As a DMARD in rheumatology, methotrexate is used for: rheumatoid arthritis (first-line DMARD; reduces synovitis, slows radiographic progression of joint erosion); psoriatic arthritis; juvenile idiopathic arthritis; inflammatory myopathies; and in combination with biological DMARDs (TNF inhibitors, JAK inhibitors) in RA — where methotrexate co-administration significantly improves biologic efficacy and reduces immunogenicity. In oncology, higher-dose or intermediate-dose methotrexate regimens are used for acute lymphoblastic leukaemia, osteosarcoma, lymphomas, and some CNS tumours. A single IM dose is used medically to terminate ectopic pregnancy.

What Is Methotrexate?

Methotrexate inhibits dihydrofolate reductase (DHFR), the enzyme that converts dihydrofolate to tetrahydrofolate — a critical step in one-carbon metabolism required for synthesis of purines and thymidylate, which are essential for DNA and RNA synthesis and cell division. In rapidly dividing cells (cancer cells, activated immune cells in inflammation), this disruption of folate metabolism inhibits cell proliferation. In RA, the anti-inflammatory effect is partly related to adenosine pathway activation and inhibition of inflammatory cytokine production, in addition to its antiproliferative effects on lymphocytes and synoviocytes.

The DMARD dosing schedule for RA is once-weekly oral dosing, typically starting at 7.5 mg/week and titrating up to 15–25 mg/week based on response and tolerability. This weekly regimen is fundamentally different from daily dosing — patients and carers must be clearly informed that methotrexate for RA is a once-weekly medicine, not daily. Medication errors from accidental daily ingestion (particularly in elderly patients) have been fatal. Prescriptions should clearly state "once weekly on [specify day]" and UK dispensing guidelines require specific weekly labelling for methotrexate dispensed in rheumatology.

Prescription vs. Over-the-Counter Status

Methotrexate is prescription-only in all markets without exception. It is a high-risk ("black box") medicine in the US — the FDA has issued multiple black box warnings covering hepatotoxicity, pulmonary toxicity, immunosuppression, embryotoxicity/teratogenicity, and mucositis/haematological toxicity. UK Medicines and Healthcare products Regulatory Agency (MHRA) also designates it as a high-risk medicine requiring specific monitoring protocols. Methotrexate requires baseline and regular monitoring: full blood count (FBC), renal function, and liver function tests (LFTs) — typically before initiation and every 3 months thereafter in stable patients. It is not available without a prescription, and dispensing it without appropriate warnings and monitoring protocols constitutes a serious clinical governance failure.

Available Strengths and Forms

For rheumatological indications: oral methotrexate 2.5 mg tablets are the standard form, with patients takin multiple tablets once weekly to achieve the target dose (e.g., 6 tablets = 15 mg). Some prescriptions use 10 mg tablets to reduce tablet burden. Injectable methotrexate for rheumatology (2.5 mg/mL or 25 mg/mL solution) is used when GI tolerance of oral tablets is poor or when higher doses are required — subcutaneous injection has higher bioavailability than oral at doses above 15 mg. For oncology: higher-concentration injectable formulations (25 mg/mL, 100 mg/mL) are used for IV infusion or intrathecal administration. Folic acid 1–5 mg/day (taken on non-methotrexate days) is co-prescribed universally to reduce methotrexate toxicity (mucositis, nausea, hepatotoxicity) without significantly compromising efficacy.

Price of Methotrexate

Generic methotrexate 2.5 mg tablets are among the least expensive prescription medicines for rheumatology. A 30-tablet supply (two to three weeks' supply at DMARD dosing) costs approximately $10–$30 at US pharmacies without insurance. With GoodRx, prices at many pharmacies fall below $10 for a 30-count. In the UK, methotrexate is dispensed on NHS prescription at standard charge (or free for patients with chronic disease exemption). Given its extremely low acquisition cost, methotrexate is considered highly cost-effective. Injectable methotrexate solution for subcutaneous use costs somewhat more but remains low-cost compared to biological DMARDs.

Frequently Asked Questions

Why is folic acid taken with methotrexate?

Methotrexate's mechanism involves disrupting folate metabolism. This disruption, while useful for its anti-inflammatory and antiproliferative effects, also causes adverse effects in normal rapidly-dividing cells (gastrointestinal mucosa, bone marrow, hair follicles) — manifesting as nausea, mouth ulcers (mucositis), and haematological side effects. Co-administering folic acid 1–5 mg daily (on different days from methotrexate) — or folinic acid (leucovorin) in higher-dose chemotherapy protocols — replenishes folate stores in normal tissues and significantly reduces these side effects without compromising methotrexate's therapeutic efficacy in RA. Current NICE and ACR guidelines recommend folic acid supplementation as standard practice with methotrexate DMARD therapy.

Why must methotrexate be avoided in pregnancy?

Methotrexate is FDA Pregnancy Category X (absolute contraindication in pregnancy). It is a potent teratogen — it causes neural tube defects, skull and facial abnormalities, limb defects, and fetal death when taken during early pregnancy. Because it inhibits folate metabolism at critical stages of fetal organogenesis, even low DMARD doses carry high teratogenic risk. Both women and men taking methotrexate for RA must use effective contraception during treatment and for at least 3–6 months after stopping (women) or 3 months after stopping (men — sperm maturation cycle). Pregnancy planning and methotrexate cessation should be discussed with the rheumatologist well in advance.

What monitoring is needed while taking methotrexate for rheumatoid arthritis?

Regular monitoring is mandatory and non-negotiable for safe methotrexate use. Baseline: FBC, U&E (renal function — methotrexate is renally cleared; impaired renal function increases toxicity), LFTs, hepatitis B and C serology, chest X-ray. During treatment: FBC + LFTs every 2 weeks for the first 3 months, then every 6–12 weeks once stable. Patients should be advised to stop methotrexate immediately and seek review if they develop unexplained fever, cough, shortness of breath (potential pneumonitis — a rare but serious pulmonary toxicity), or marked nausea/mouth ulcers. Renal function is particularly important — methotrexate is cleared via kidneys, and renal impairment causes accumulation and dramatically increased toxicity.

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