Quick answer: Leflunomide is a disease-modifying anti-rheumatic drug (DMARD) used for rheumatoid and psoriatic arthritis. It usually takes one to three months to work. You will need regular blood tests plus blood pressure and weight checks. Common side effects include diarrhoea, feeling sick and hair thinning. Leflunomide stays in the body for a long time, so plan pregnancy carefully with your team. Never change your dose yourself.
What leflunomide does
Leflunomide is a tablet that slows down the activity of certain immune cells that drive inflammation in inflammatory arthritis. By calming this process it reduces joint pain, swelling and stiffness, and helps protect joints from long-term damage. It is used for rheumatoid arthritis and psoriatic arthritis, often when methotrexate is not suitable or has not worked well enough. It is sometimes combined with other treatments.
Like other DMARDs, it is a long-term treatment rather than a quick painkiller. Read our overview of DMARDs and biologics to see how the options compare.
Taking leflunomide
Leflunomide is taken as a tablet once a day, with or without food. Some teams start with a higher "loading" dose for a few days, but many do not, because it can increase side effects. Your team will decide what suits you. Take it exactly as your rheumatology team advises and never change the dose yourself. If you miss a dose, check your leaflet or ask a pharmacist.
How long until it works?
Most people notice a difference within four to six weeks, and the full effect can take up to three months or a little longer. During this time your team may offer steroids or anti-inflammatory painkillers to help with symptoms.
Monitoring: blood tests, blood pressure and weight
Leflunomide can affect the liver, blood cells and blood pressure, so regular checks are part of treatment. Before you start you will usually have baseline blood tests, a blood pressure reading and your weight recorded. After that, checks are frequent in the first months and then spaced out once things are stable. Your team or GP, under shared-care arrangements, will tell you your schedule. Typical checks are:
- Full blood count.
- Liver function tests.
- Blood pressure, because leflunomide can raise it.
- Weight, because some people lose weight on it.
Keeping your own record of results and blood pressure readings can help. A home blood pressure monitor is useful if your team suggests it.
Common side effects
Many people take leflunomide without problems. When side effects happen, they are often mild and more common in the early months. They can include:
- Diarrhoea, feeling sick or tummy pain.
- Raised blood pressure.
- Headaches or dizziness.
- Hair thinning, which usually improves and may reverse after stopping.
- Rash or itchy skin.
- Mouth ulcers.
- Tingling or numbness in the hands or feet, which you should report.
- Weight loss.
If diarrhoea or other side effects are bothering you, talk to your team rather than just stopping. There are often ways to help, and stopping suddenly can let your arthritis flare.
When to get urgent advice
Contact your GP or rheumatology advice line the same day, or call NHS 111, if you have:
- A fever, sore throat, chills or other signs of infection.
- Unexplained bruising, bleeding or looking very pale.
- Yellow skin or eyes, dark urine or pain in the upper right of your tummy.
- A new cough or breathlessness.
- A severe rash, blistering or mouth sores.
Call 999 if you have signs of a severe allergic reaction, such as swelling of the face or throat or difficulty breathing.
Alcohol
Because leflunomide and alcohol can both affect the liver, you will usually be advised to keep alcohol low, and your team may give you a specific limit. Follow their advice. Our guide to arthritis and alcohol explains more.
Pregnancy, fathering a child and the washout
Leflunomide is not safe in pregnancy. It also stays in the body for a long time after the last tablet, sometimes up to two years. That means family planning needs careful thought:
- Use reliable contraception while taking leflunomide and for as long afterwards as your team advises.
- If you are thinking about pregnancy, talk to your team well in advance. They can arrange a "washout", where another medicine is taken to clear leflunomide from the body more quickly, followed by blood tests to confirm levels are low enough.
- Men who are planning to father a child are usually advised to discuss stopping leflunomide and having a washout too.
- If you become pregnant unexpectedly, contact your team straight away. Do not just stop the tablets without speaking to them.
Our guide to arthritis and pregnancy covers planning in more detail. The long stay in the body also matters if you have serious side effects, as a washout can be used to speed up clearance.
Infections and vaccines
Leflunomide can make you slightly more prone to infections. Wash your hands regularly, keep up to date with the vaccines your team recommends, and seek advice early if you feel unwell with an infection. Live vaccines are generally avoided while you take leflunomide. Read our guide to vaccines on DMARDs and biologics.
Other medicines
Leflunomide can interact with some other medicines, including some that affect the liver or blood. Always tell pharmacists, dentists and doctors that you take it, and check before starting new prescriptions, over-the-counter remedies or supplements. See our guide to medicine and supplement interactions.
If it is not working, or you need to stop
Not every medicine suits every person. If leflunomide has not helped enough after a fair trial, or side effects are a problem, your team may adjust the dose, add another medicine or switch to a different treatment, such as another DMARD or a biologic. Stopping should be planned with your team, because inflammation can return quickly without treatment. Our guide to stopping arthritis medicines safely explains why. If you are worried about taking leflunomide long term, raise it at your next review or call your advice line. Your concerns matter, and there is usually more than one option.
Frequently asked questions
How long does leflunomide take to work?
Most people notice some benefit in four to six weeks, with the full effect taking up to three months or a little longer.
Can I drink alcohol on leflunomide?
You will usually be advised to keep alcohol to a low level because both can affect the liver. Follow the limit your rheumatology team gives you.
Why does leflunomide need a washout?
Leflunomide stays in the body for a long time. A washout uses another medicine to remove it faster, for example before a planned pregnancy or after a serious side effect.
Does leflunomide cause hair loss?
Some people notice hair thinning. It is often mild and usually improves over time or after stopping. Mention it to your team.
Why do I need blood pressure checks on leflunomide?
Leflunomide can raise blood pressure in some people, so it is checked before and during treatment.
Can men take leflunomide when trying for a baby?
Men are usually advised to discuss stopping leflunomide, and possibly a washout, with their team before trying to conceive.
Sources and further reading
This guide is for general education and is not a substitute for personal medical advice. Everyone's situation is different, so always follow the advice of your own GP, pharmacist or rheumatology team. If you feel very unwell, call 999 or go to A&E. For urgent advice, contact NHS 111.