What is methotrexate?

Methotrexate is one of the most effective and widely used medications in rheumatology. It’s been a cornerstone of treatment for rheumatoid arthritis since the 1980s and is also used for psoriatic arthritis, lupus, vasculitis, and other autoimmune conditions.

At the low doses we use in rheumatology (typically 7.5–25 mg once per week), methotrexate works as an immunomodulator — it calms an overactive immune system rather than suppressing it entirely.

How to take it

Once per week — always on the same day (e.g., every Saturday). This is not a daily medication.
Available as tablets or a subcutaneous injection (Otrexup, Rasuvo, or generic prefilled syringes).
Take folic acid daily (usually 1 mg) to reduce side effects. Your doctor may prescribe a higher dose or folinic acid (leucovorin) on specific days.

Important: Never take methotrexate daily. If your pharmacy label is confusing, call us before taking an extra dose.

What to expect when starting

Most patients notice improvement within 6–12 weeks, though some respond sooner. Methotrexate is a slow-acting medication — it works by gradually reducing inflammation, not by masking symptoms quickly.

During the first few months you might experience:

Mild nausea on dosing day (taking it at bedtime or splitting the dose can help)
Fatigue for 1–2 days after dosing
Mild mouth sores (usually means you need more folic acid — let us know)

These side effects often improve over time or with dose adjustments.

Managing “methotrexate fog” and fatigue

Many patients notice fatigue or a mental fog around dosing day — sometimes called “methotrexate fog.” This is real and common. A few strategies can help:

Schedule your dose strategically — take methotrexate on a Friday evening or before a lighter day so any fatigue falls on a recovery day
Take it at bedtime — you may sleep through the worst of the fog
Stay well-hydrated on dosing day and the day after
Caffeine can help with next-day grogginess
Folic acid (which you should already be taking) also helps reduce fatigue

If your physician recommends dextromethorphan (DXM) to help with methotrexate-related brain fog, the typical approach is a single 20 mg dose (available over-the-counter in cough products) taken the evening of or morning after your methotrexate dose. Use a DXM-only formulation — not combination cold products that contain acetaminophen, antihistamines, or decongestants. DXM can interact with certain medications (especially antidepressants), so only use it if specifically discussed with your doctor.

Lab monitoring

You will need regular blood work while on methotrexate, typically:

Complete blood count (CBC) — checks your blood cells
Comprehensive metabolic panel (CMP) — checks liver and kidney function

We usually check labs every 4–8 weeks when starting, then every 2–3 months once stable. This is how we ensure the medication remains safe for you.

Side effects to watch for

Persistent nausea, vomiting, or loss of appetite beyond the first dosing day
Mouth sores that don’t heal
Fever, chills, or signs of infection (methotrexate can lower white blood cell counts)
Unusual bruising or bleeding
Shortness of breath or dry cough (rare but important — can indicate lung sensitivity)
Yellowing of the skin or eyes

Things to avoid

Alcohol — limit to occasional, moderate use (1–2 drinks per week maximum). Alcohol and methotrexate are both processed by the liver.
Pregnancy — methotrexate causes birth defects and must be stopped at least 3 months before planning conception (for both men and women). Use reliable contraception.
Live vaccines — such as the live shingles vaccine (Zostavax) or live nasal flu spray. Inactivated vaccines (flu shot, COVID, Shingrix) are safe and recommended.

Injection vs. tablets

If you experience nausea with tablets, switching to the subcutaneous injection often helps significantly. The injection:

Bypasses the GI tract, reducing nausea
Has more consistent absorption
Is a small, easy-to-use prefilled syringe (similar to insulin)

Ask us if you’d like to switch forms.

Frequently asked questions

Will methotrexate weaken my immune system? At rheumatology doses, methotrexate modulates rather than broadly suppresses your immune system. You may be slightly more susceptible to infections, but most patients live normally — work, travel, and socialize without restrictions.

Can I get vaccinated? Yes — inactivated vaccines are recommended. Avoid live vaccines. Talk to us before any new vaccination.

What if I miss a dose? Take it as soon as you remember within 2–3 days of your usual day. If it’s closer to your next dose, skip the missed one. Never double up.

How long will I need to take it? This varies by condition. Many patients take methotrexate for years because it’s well-tolerated and effective long-term. We’ll discuss this as part of your ongoing care plan.

This handout is provided for educational purposes and does not replace individualized medical advice. Always follow the specific instructions given by your rheumatologist.

Methotrexate: What You Need to Know