Cobimetinib is used along with vemurafenib (Zelboraf) to treat certain types of melanoma (a type of skin cancer) that cannot be treated with surgery or that has spread to other parts of the body. Cobimetinib is in a class of medications called kinase inhibitors. It works by blocking the action of an abnormal protein that signals cancer cells to multiply. This helps slow or stop the spread of cancer cells.

Side Effects Of Cobimetinib

Cobimetinib may cause side effects. Tell your doctor if any of these symptoms are severe or do not go away:

  • mouth ulcers
  • hair loss
  • diarrhea

Some side effects can be serious. If you experience any of these symptoms or those in the WARNINGS AND PRECAUTIONS section, call your doctor immediately or get emergency medical treatment:

  • rash that covers a large area of your body, blisters, or peeling skin
  • changes in skin appearance
  • new wart
  • skin sore or red bump that bleeds or does not heal
  • change in size or color of a mole
  • unusual bleeding or bruising
  • tarry or black stools
  • blood in the urine
  • unusual vaginal bleeding
  • headache
  • dizziness
  • rapid, irregular, or pounding heartbeat
  • coughing or wheezing
  • shortness of breath
  • swelling of the face, arms, legs, ankles, or feet
  • tiredness
  • muscle pain or weakness
  • change in vision, including seeing halos (blurred outline around objects)
  • yellowing of the skin or eyes
  • dark-colored (tea-colored) urine
  • pain in the upper right part of the stomach
  • nausea
  • vomiting
  • loss of appetite
  • Cobimetinib may increase the risk that you will develop new skin cancers. Talk to your doctor about the risks of taking this medication.

Cobimetinib may cause other side effects. Call your doctor if you have any unusual problems while taking this medication.

Warnings & Precautions

Before taking cobimetinib:

  • tell your doctor and pharmacist if you are allergic to cobimetinib, any other medications, or any of the ingredients in cobimetinib tablets. Ask your pharmacist for a list of the ingredients.
  • tell your doctor and pharmacist what other prescription and nonprescription medications, vitamins, nutritional supplements, and herbal products you are taking or plan to take. Be sure to mention any of the following: anticoagulants (blood thinners) such as warfarin (Coumadin, Jantoven), carbamazepine (Carbatrol, Epitol, Tegretol), ciprofloxacin (Cipro), clarithromycin (Biaxin, in Prevpac), efavirenz (Sustiva, in Atripla), erythromycin (E.E.S., E-Mycin, Erythrocin), indinavir (Crixivan), itraconazole (Onmel, Sporanox), ketoconazole (Extina, Ketozole, Nizoral), nefazodone, nelfinavir (Viracept), phenytoin (Dilantin, Phenytek), rifampin (Rifadin, Rimactane, in Rifamate, in Rifater), and ritonavir (Norvir, in Kaletra, in Viekira Pak). Your doctor may need to change the doses of your medications or monitor you carefully for side effects. Many other medications may also interact with cobimetinib, so be sure to tell your doctor about all the medications you are taking, even those that do not appear on this list.
  • tell your doctor what herbal products you are taking, especially St. John’s Wort. Do not take St. John’s Wort while you are taking cobimetinib.
  • tell your doctor if you have or have ever had have skin conditions other than melanoma; bleeding problems; vision problems; any condition that affects your muscles; or heart or liver disease.
  • you should know that cobimetinib may decrease fertility in men and women. However, you should not assume that you or your partner cannot become pregnant. Tell your doctor if you are pregnant or plan to become pregnant. Use a reliable method of birth control to prevent pregnancy during your treatment and for 2 weeks after you stop taking cobimetinib. Talk to your doctor about birth control methods that will work for you. If you become pregnant while taking cobimetinib, call your doctor immediately. Cobimetinib may harm the fetus.
  • tell your doctor if you are breastfeeding. You should not breastfeed while taking cobimetinib and for 2 weeks after your last dose.
  • plan to avoid unnecessary or prolonged exposure to sunlight and to wear protective clothing, sunglasses, lip balm and sunscreen (SPF 30 or higher). Cobimetinib may make your skin sensitive to sunlight.

Dosage Of Cobimetinib

Cobimetinib comes as a tablet to take by mouth with or without food. It is usually taken once daily for the first 21 days of a 28-day cycle. Take cobimetinib at around the same time every day. Follow the directions on your prescription label carefully, and ask your doctor or pharmacist to explain any part you do not understand. Take cobimetinib exactly as directed. Do not take more or less of it or take it more often than prescribed by your doctor.

If you vomit after taking cobimetinib do not take another dose. Continue your regular dosing schedule.

Your doctor may decrease your dose of cobimetinib or permanently or temporarily stop your treatment. This depends on how well the medication works for you and the side effects you experience. Be sure to tell your doctor how you are feeling during your treatment with cobimetinib.

Ask your pharmacist or doctor for a copy of the manufacturer’s information for the patient.


Keep all appointments with your doctor and the laboratory. Your doctor will order certain lab tests to check your body’s response during and after therapy. Your doctor will check your skin for any changes before, every 2 months during your treatment, and for up to 6 months after treatment.

It is important for you to keep a written list of all of the prescription and nonprescription (over-the-counter) medicines you are taking, as well as any products such as vitamins, minerals, or other dietary supplements. You should bring this list with you each time you visit a doctor or if you are admitted to a hospital. It is also important information to carry with you in case of emergencies.


All information has been provided courtesy of MedLinePlus from the National Library of Medicine and from the FDA.