Leflunomide: what it treats, how to take it, side effects
Last updated September 3, 2026.
Leflunomide is a DMARD - a disease-modifying antirheumatic drug that decreases inflammation and slows rheumatoid arthritis itself. You may know it as Arava. Slows the disease, not just the pain - with two warnings that lead every conversation: liver and pregnancy.
What does it treat?
Rheumatoid arthritis - the autoimmune condition where the body attacks its own joints - alone or with other medications, improving physical function by slowing the disease's progress.
How do you take it?
One tablet once a day, sometimes with a larger loading dose for the first 3 days. Exactly as directed - and say how you are feeling during treatment, because certain side effects mean the dose drops or stops. The drug lingers in the body for a long time after stopping; a specific elimination treatment exists when it needs to leave fast. Missed dose: take it when you remember unless the next one is close; never double up.
Side effects to know
- Common: diarrhea, vomiting, heartburn, headache, dizziness, weight loss, back or joint pain, weakness, and hair loss.
- Serious - call your doctor immediately or get emergency care: rash with or without fever, hives, itching, swelling of face, eyes, mouth, throat, tongue, or lips, red, blistering, or peeling skin, skin sores or ulcers, mouth sores, trouble breathing, shortness of breath, new or worsening cough, chest pain, pale skin, unusual tiredness, unusual bruising or bleeding, and pain, burning, numbness, or tingling in hands, arms, legs, or feet. From the liver warning: nausea, extreme tiredness, lack of energy, loss of appetite, pain in the upper right stomach, yellowing skin or eyes, dark urine, or flu-like symptoms.
Who should not take it?
Not during pregnancy, planned pregnancy, or planned fatherhood - the boxed warning: birth control for both partners during treatment and for 2 years after, unless the elimination treatment clears the drug sooner; a pregnancy on it is an immediate call. Liver disease or heavy alcohol history can rule it out - the liver warning is real, and the blood tests are how it is policed. Flag immune problems and current infections. Vaccines: no live vaccines without your doctor's approval.
When is it an emergency?
Throat swelling, trouble breathing, a blistering or peeling rash, or yellowing eyes is a 911 call. For an overdose, call Poison Control at 1-800-222-1222. Pymander's escalation routing is built and tested specifically for this class of decision; see the safety architecture working paper.
What a Pymander AI doctor consult looks like
Illustrative example, not a real member's messages.
Common questions
Why are the pregnancy rules so strict - and for so long?
The drug can harm a fetus and it clears from the body slowly - so the label requires effective birth control during treatment and for 2 years after, for women and for men fathering a child, unless the elimination treatment (cholestyramine or charcoal) is used to clear it faster. A pregnancy on leflunomide is an immediate doctor call. Planning a family inside the 2-year window: talk to your doctor first - the elimination treatment plus blood-test confirmation is the safe path.
What is the liver warning about?
Leflunomide can cause liver damage that can be life-threatening - the risk is greatest with existing liver disease, heavy alcohol history, or interacting medications. The defense is the blood-test schedule your doctor set: the tests catch trouble before symptoms. The symptom set - nausea, extreme tiredness, loss of appetite, right-upper-stomach pain, yellowing skin or eyes, dark urine - is an immediate call. Alcohol on this drug is a conversation, not an assumption.
How long until it works?
Weeks to months - DMARDs retrain the immune attack, which is slow by design: expect the first real change around 4 to 8 weeks, building beyond. The loading dose in the first 3 days speeds the start. Judge it by morning-stiffness minutes and joint counts, not day-to-day feel. Stopping because "nothing happened" at week two is how the joint damage wins.
What is the elimination treatment?
Leflunomide's active metabolite recirculates and can persist for up to 2 years - when it must leave fast (pregnancy plans, serious side effects), a course of cholestyramine or activated charcoal binds it in the gut and clears it in days, confirmed by blood tests. It exists, it works, and it is the reason "stopped the drug" and "drug is gone" are different sentences on leflunomide.
Why do I need to report infections and avoid live vaccines?
The drug dampens the immune system by design - infections can take hold harder and longer, so fever, chills, persistent sore throat, or a cough that will not quit gets reported promptly. Live vaccines can cause the infection they are meant to prevent in a suppressed immune system: no live vaccines without your doctor's explicit approval, and household contacts' vaccines are worth a mention too.
What happens if I miss a dose of leflunomide?
Take it as soon as you remember, unless it is almost time for the next one - then skip it and never double up. Given how long the drug persists in the body, a single missed dose barely moves the level - the habit matters for the months-long arc, not the single day. Same time each morning keeps it automatic.