Ritlecitinib belongs to the class of medications called Janus kinase (JAK) and tyrosine kinase (TEC) inhibitors. It is used by adults and adolescents 12 years of age and older to treat severe alopecia areata.

Alopecia areata is an autoimmune disease. This means that the body's immune system fails to recognize its own tissue and views it as a foreign invader. In the case of alopecia areata, the immune system attacks the hair follicles, causing hair loss.

Ritlecitinib changes the way your immune system works and reduces inflammation, allowing hair to regrow.

This medication may be available under multiple brand names and/or in several different forms. Any specific brand name of this medication may not be available in all of the forms or approved for all of the conditions discussed here. As well, some forms of this medication may not be used for all of the conditions discussed here.

Your doctor may have suggested this medication for conditions other than those listed in these drug information articles. If you have not discussed this with your doctor or are not sure why you are taking this medication, speak to your doctor. Do not stop taking this medication without consulting your doctor.

Do not give this medication to anyone else, even if they have the same symptoms as you do. It can be harmful for people to take this medication if their doctor has not prescribed it.

The recommended dose of ritlecitinib is 50 mg (1 capsule) taken by mouth, once a day.

It should be swallowed whole with some water. Do not crush or chew the capsule. Ritlecitinib may be taken with food or on an empty stomach.

Many things can affect the dose of medication that a person needs, such as body weight, other medical conditions, and other medications. If your doctor has recommended a dose different from the ones listed here, do not change the way that you are taking the medication without consulting your doctor.

It is important to take this medication exactly as prescribed by your doctor.

If you miss a dose, take it as soon as possible and continue with your regular schedule. If it is less than 8 hours until your next dose, skip the missed dose and continue with your regular dosing schedule. Do not take a double dose to make up for a missed one. If you are not sure what to do after missing a dose, contact your doctor or pharmacist for advice.

Store this medication at room temperature, protect it from light and moisture, and keep it out of the reach of children.

Each opaque capsule with a yellow body printed with "RCB 50" and a blue cap printed with "Pfizer" in black, contains 80.1228 mg of ritlecitinib tosylate, equivalent to 50 mg of ritlecitinib. Nonmedicinal ingredients: crospovidone, FD&C Blue No. 1, ferric oxide yellow, glyceryl dibehenate, hypromellose, lactose monohydrate, microcrystalline cellulose, and titanium dioxide.

Do not take this medication if you:

• are allergic to ritlecitinib or any ingredients of the medication
• are or may be pregnant
• are breast-feeding
• have severely decreased liver function

Many medications can cause side effects. A side effect is an unwanted response to a medication when it is taken in normal doses. Side effects can be mild or severe, temporary or permanent.

The side effects listed below are not experienced by everyone who takes this medication. If you are concerned about side effects, discuss the risks and benefits of this medication with your doctor.

The following side effects have been reported by at least 1% of people taking this medication. Many of these side effects can be managed, and some may go away on their own over time.

Contact your doctor if you experience these side effects and they are severe or bothersome. Your pharmacist may be able to advise you on managing side effects.

• acne
• diarrhea
• dizziness
• rash

Although most of the side effects listed below don't happen very often, they could lead to serious problems if you do not seek medical attention.

Check with your doctor as soon as possible if any of the following side effects occur:

• inflamed hair follicles or pores
• signs of a blood clot in the arm or leg (tenderness, pain, swelling, warmth, or redness in the arm or leg) or lungs (difficulty breathing, sharp chest pain that is worst when breathing in, coughing, coughing up blood, sweating, or passing out)
• signs of clotting problems (e.g., unusual nosebleeds, bruising, blood in urine, coughing blood, bleeding gums, cuts that don't stop bleeding)
• signs of infection (symptoms may include fever or chills, severe diarrhea, shortness of breath, prolonged dizziness, headache, stiff neck, weight loss, or listlessness)
• symptoms of herpes zoster infection (shingles; e.g., painful skin rash of fluid-filled blisters, itching, headache, fatigue, fever, chills)

Stop taking the medication and seek immediate medical attention if any of the following occur:

• signs of a serious allergic reaction (e.g., abdominal cramps, difficulty breathing, nausea and vomiting, or swelling of the face and throat)
• signs of a heart attack (e.g., chest pain or pressure, pain extending through shoulder and arm, nausea and vomiting, sweating)
• signs of stroke (e.g., sudden or severe headache; sudden loss of coordination; vision changes; sudden slurring of speech; or unexplained weakness, numbness, or pain in arm or leg)

Some people may experience side effects other than those listed. Check with your doctor if you notice any symptom that worries you while you are taking this medication.

Before you begin using a medication, be sure to inform your doctor of any medical conditions or allergies you may have, any medications you are taking, whether you are pregnant or breast-feeding, and any other significant facts about your health. These factors may affect how you should use this medication.

Bleeding:  Ritlecitinib may cause a reduced number of platelets in the blood, which can make it difficult to stop cuts from bleeding. If you notice any signs of bleeding, such as frequent nosebleeds, unexplained bruising, or black and tarry stools, notify your doctor as soon as possible. Your doctor will order routine blood tests to make sure potential problems are caught early.

Blood clots: This medication may increase the chance of blood clot formation, causing reduction of blood flow to organs or the extremities.

If you experience symptoms such as sharp pain and swelling in the leg, difficulty breathing, chest pain, blurred vision or difficulty speaking, contact your doctor immediately.

Cancer: Rarely, people taking ritlecitinib and similar medications have developed cancer, including lymphoma, non-melanoma skin cancer, and lung cancer. People with rheumatoid arthritis taking similar medications over long periods of time may also have a higher risk of developing lymphoma. Discuss any concerns you have with your doctor.

Heart attack and stroke: Ritlecitinib may increase the risk for major heart problems such as heart attack and stroke. If you have risk factors for heart disease such as high blood pressure, high cholesterol, or are a smoker or have a history of smoking your risk may be increased.

If you experience symptoms such as chest pain, difficulty breathing, pain extending through shoulder and arm, nausea and vomiting, sweating, weakness on one side of the body, or slurred speech, get immediate medical attention. 

Infection: This medication reduces your body's response to infection. People taking ritlecitinib are at an increased risk of developing serious infections that can be difficult to treat and may cause hospitalization or death. These infections include tuberculosis and fungal infections, as well as infections caused by bacteria and viruses. These infections are more likely to occur if you are taking another medication that reduces the activity of the immune system.

If you have been exposed to tuberculosis, have a history of serious or recurrent infections or have medical conditions that may increase the likelihood of developing infections, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Other conditions that may be reactivated while taking ritlecitinib include shingles, herpes zoster infections, or hepatitis B.

If possible, avoid contact with people with contagious infections. Tell your doctor immediately if you notice signs of an infection, such as fever or chills, severe diarrhea, shortness of breath, prolonged dizziness, headache, stiff neck, weight loss, or listlessness.

Liver function:  Decreased liver function or liver disease may cause this medication to build up in the body causing side effects. If you have a history of liver problems, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

People who have had hepatitis B in the past may experience a flare-up of the disease while taking ritlecitinib.

Your doctor will recommend regular liver tests while you are taking this medication. If you have a history of hepatitis B infection, it is possible that this infection may flare up while taking ritlecitinib.

Vaccinations: Vaccines that are given during treatment with ritlecitinib may not be as effective as expected. Also, people taking this medication should not receive certain vaccines. Talk to your doctor about whether any vaccines you are scheduled to take should not be used with this medication.

Pregnancy: This medication should not be used during pregnancy unless the benefits outweigh the risks. If you become pregnant while taking this medication, contact your doctor immediately. People who could become pregnant should use appropriate birth control while taking ritlecitinib and for at least 1 month after taking the last dose of medication.

Breast-feeding: It is not known if ritlecitinib passes into breast milk. If you are breast-feeding and taking this medication, it may affect your baby. Talk to your doctor about whether you should continue breast-feeding.

Children: The safety and effectiveness of using this medication have not been established for children under 12 years of age.

For a full list of interactions, use the Drug Interaction Checker available on the Drugs.com website.

If you are taking other medications, speak with your doctor or pharmacist. Depending on your specific circumstances, your doctor may want you to:

• stop taking one of the medications,
• change one of the medications to another,
• change how you are taking one or both of the medications, or
• leave everything as is.

An interaction between two medications does not always mean that you must stop taking one of them. Speak to your doctor about how any drug interactions are being managed or should be managed.

Tell your doctor or prescriber about all prescription, over-the-counter (non-prescription), and herbal medications you are taking. Also tell them about any supplements you take. Since caffeine, alcohol, the nicotine from cigarettes, or street drugs can affect the action of many medications, you should let your prescriber know if you use them.