Does Koselugo (selumetinib) cure neurofibromatosis type 1 (NF1)?

No, Koselugo (selumetinib) [doesn’t cure NF1](https://www.cancer.gov/news-events/press-releases/2020/selumetinib-nf1-children). But it can help slow or stop the growth of tumors called plexiform neurofibromas (PNs) in people with NF1. In [studies](https://www.accessdata.fda.gov/drugsatfda_docs/label/2025/213756s006lbl.pdf), some had tumors that stayed the same size or got smaller after taking Koselugo (selumetinib) for several months. For some children, it kept working for [at least 3 years](https://pmc.ncbi.nlm.nih.gov/articles/PMC7305659/). Talk to your NF1 specialist to learn what to expect from treatment.

Can you take vitamin supplements while taking Koselugo (selumetinib)?

Talk to your care team before taking any vitamins or supplements. Koselugo (selumetinib) capsules contain vitamin E. Taking more vitamin E than the [recommended daily amount](https://ods.od.nih.gov/factsheets/VitaminE-Consumer/) can raise the risk of bleeding. Ask a healthcare professional or pharmacist to check if a supplement has vitamin E and if it’s safe for you.

Koselugo

selumetinib

Used for Neurofibromatosis

Koselugo (selumetinib) is a targeted therapy that works as a MEK inhibitor. It treats certain tumors caused by a genetic condition called neurofibromatosis type 1 (NF1). More specifically, it’s for adults and children 1 year and older with NF1 who have plexiform neurofibromas (PN), or small tumors around nerve tissue. Koselugo (selumetinib) comes as capsules and oral granules that are taken by mouth twice a day. But it can cause side effects like vomiting, diarrhea, and rash.

Reviewed by:

Julia Lee, PharmD, BCOP

Cydnee Ng, PharmD

Last reviewed on November 24, 2025

What is Koselugo (selumetinib)?

What is Koselugo (selumetinib) used for?

Neurofibromatosis type 1 (NF1) with symptomatic plexiform neurofibromas (PN) that can’t be removed by surgery

How Koselugo (selumetinib) works

Koselugo (selumetinib) is a type of kinase inhibitor called a MEK inhibitor. It blocks a protein in the body called MEK, which is part of a signaling pathway that’s too active in people with NF1. This overactive signaling causes too much cell growth, leading to tumors like plexiform neurofibromas (PN).

When Koselugo (selumetinib) blocks the MEK protein, the signaling pathway gets disrupted. This stops the tumors from growing or spreading as well.

When does Koselugo (selumetinib) start working?Time passed since treatment started:

HOURS

DAYS

WEEKS

MONTHS

Full effect

Drug facts

Common BrandsKoselugo

Drug ClassMEK inhibitor

Controlled Substance ClassificationNot a controlled medication

Generic StatusNo lower-cost generic available

AvailabilityPrescription only

Side effects of Koselugo (selumetinib)

The following side effects may get better over time as your body gets used to the medication. Let your healthcare provider know immediately if you continue to experience these symptoms or if they worsen over time.

Common Side Effects

Children:

Nausea
Vomiting
Diarrhea
Higher creatine phosphokinase levels
Dry skin
Acne-like rash
Nail infection
Fever

Adults:

Rash
Acne-like rash
Diarrhea

Less Common Side Effects

Children:

Stomach pain
Constipation
Rash or skin irritation
Itching
Muscle, bone, or joint pain
Mouth sores
Tiredness
Headache
Lower white blood cells
Hair changes (e.g., hair loss, hair color change)
Higher liver enzyme levels
Lower hemoglobin levels

Adults:

Nausea
Vomiting
Muscle, bone, or joint pain
Swelling of the legs or feet
Tiredness
Higher creatine phosphokinase levels
Higher liver enzyme levels
Lower hemoglobin levels

Koselugo (selumetinib) serious side effects

Contact your healthcare provider immediately if you experience any of the following.

Heart problems: coughing or wheezing that doesn’t go away, feeling short of breath, swelling in the ankles or feet, feeling tired, fast heartbeat
Eye problems: blurry vision, vision loss, dark spots in vision (floaters), other changes in vision
Diarrhea that won’t stop
Skin problems: widespread rash, raised bumps on your skin, acne-like bumps on your skin, itchy rash, skin peeling, blisters
Possible muscle problems: muscle aches or pain, muscle spasms, muscle weakness, dark red urine

When do Koselugo (selumetinib) possible side effects begin and end?

Time passed since treatment started:

HHOURS

DDAYS

WWEEKS

MMONTHS

Acne-like rash

Dry skin

Risk of diarrhea

Risk of nail infection

If a line continues to the right, you'll likely keep experiencing this side effect once it starts.

Source: FDA

The following Koselugo (selumetinib) side effects have also been reported

Side effects that you should report to your care team as soon as possible:

Allergic reactions—skin rash, itching, hives, swelling of the face, lips, tongue, or throat
Bleeding—bloody or black, tar-like stools, vomiting blood or brown material that looks like coffee grounds, red or dark brown urine, small red or purple spots on skin, unusual bruising or bleeding
Blurry vision, vision loss, seeing wavy or bent objects or blind spots with dark, light, or flashing spots
Heart failure—shortness of breath, swelling of the ankles, feet, or hands, sudden weight gain, unusual weakness or fatigue
Muscle injury—unusual weakness or fatigue, muscle pain, dark yellow or brown urine, decrease in amount of urine
Redness, swelling, and blistering of the skin over hands and feet
Severe or prolonged diarrhea
Stomach pain that is severe, does not go away, or gets worse
Sudden or severe stomach pain, bloody diarrhea, fever, nausea, vomiting

Side effects that usually do not require medical attention (report these to your care team if they continue or are bothersome):

Dry skin
Headache
Pain, redness, or swelling with sores inside the mouth or throat
Nail infection—redness, swelling, warmth, or pain around the nail
Nausea
Stomach pain
Vomiting

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Avg retail price

$5891.00(Save 29.64%)

GoodRx discount

$4144.80

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Pros and cons of Koselugo (selumetinib)

Pros

Taken by mouth
Oral granules also available for people who can’t swallow pills whole
Can help shrink or keep NF1 PNs from growing when surgery can’t completely remove them

Cons

Must take twice a day
Can cause rash, dry skin, and upset stomach
Can affect how well the heart is working, so need periodic heart ultrasounds (echocardiograms)

Pharmacist tips for Koselugo (selumetinib)

Take Koselugo (selumetinib) twice a day, with or without food. But avoid grapefruit, grapefruit juice, and Seville oranges. These foods can raise the risk of side effects from the medication.
If you miss a dose of Koselugo (selumetinib), take the medication as soon as possible. But if the next dose is in less than 6 hours, skip the missed dose and wait for the next dose to take the usual amount. Don’t double up to make up for a missed dose because it can lead to more side effects.
If you vomit right after taking Koselugo (selumetinib), don’t take another dose. Just wait to take the usual dose at the next scheduled time.
Koselugo (selumetinib) can cause dry skin and rash. If your skin starts getting dry, moisturizer can help. But if it gets too uncomfortable or if you have an acne-like rash, tell your NF1 specialist. They can suggest other ways to manage this.
Koselugo (selumetinib) often causes diarrhea. To manage this side effect, your care team might suggest giving anti-diarrheal medication, like loperamide (Imodium A-D), after the first loose or watery stool. Be sure to drink plenty of fluids to stay hydrated. If diarrhea won’t stop or if you have signs of severe dehydration, get medical help right away.
Call your care team right away if you have blurry vision, see floaters, or notice other changes in your eyesight. Koselugo (selumetinib) can cause vision changes that can sometimes be serious. An eye specialist can check your eyes to see what’s going on.
Make sure you get your eye exams and heart scans on time. Your NF1 specialist will order these tests regularly to watch for possible dangerous side effects from Koselugo (selumetinib). Ask your care team what the results mean.
Tell your care team and pharmacist about all the medications you take or plan to take. Koselugo (selumetinib) can interact with many medications. Some, like St. John’s wort, can affect how well Koselugo (selumetinib) works. Others, like fluconazole (Diflucan), can make side effects more likely. Your care team can make changes to the treatment plan to keep you safe.

Tips for Koselugo (selumetinib) capsules

Swallow the capsule whole. Don’t chew, dissolve, crush, or open them because it can affect how the medication works.
Don’t take any supplements that contain vitamin E unless your care team says it’s okay. Koselugo (selumetinib) capsules contain vitamin E. Too much vitamin E can be harmful and raise your bleeding risk.

Tips for Koselugo (selumetinib) oral granules

Open the prescribed number of capsules and sprinkle the granules onto a spoon or small cup of 1 to 3 teaspoons of soft food. This can be smooth yogurt or fruit puree (apple, banana, pear, or strawberry). Don’t mix with liquids or anything made with grapefruit or Seville oranges.
After it’s prepared, take the mixture within 30 minutes while sitting up straight. Make sure to swallow it all without chewing.
If you’re using a spoon: Take 1 capsule of oral granules at a time. Repeat the steps to prepare and take each capsule until you've taken your full dose.
If you’re using a small cup: After you first take the dose, add a little more of the same food into the cup and then eat it. This makes sure you take your full dose.
Don't swallow or chew the capsule shells. Also don’t dissolve the capsule shells. Don’t chew or crush the oral granules.
Throw away any mixture left after 30 minutes of preparing. If you don't take the full dose in time, wait until the next scheduled time to prepare and take the medication again.
Store Koselugo (selumetinib) granules at room temperature (up to 77ºF). If it’s hotter than 86ºF, keep them in the fridge (between 36ºF and 46ºF). If you need to go somewhere with the medication, place it in a cooler bag with a cool pack. Heat can make the granules stick together or to the capsule shell and affect how much medication you actually take.

Common questions about Koselugo

No, Koselugo doesn’t cure NF1. But it can help slow or stop the growth of tumors called plexiform neurofibromas (PNs) in people with NF1. In studies, some had tumors that stayed the same size or got smaller after taking Koselugo for several months. For some children, it kept working for at least 3 years. Talk to your NF1 specialist to learn what to expect from treatment.

Koselugo isn't a type of traditional chemotherapy. It’s a targeted therapy that works on a specific protein in the body called MEK. In people with NF1, MEK is too active and it leads to tumors called plexiform neurofibromas (PNs). By blocking MEK, Koselugo helps stop the PNs from growing or spreading. This is different from traditional chemotherapy, which affects all fast-growing cells in the body.

The most common side effects of Koselugo are stomach upset and rash. If these become too hard for you to handle, let your care team know. They can recommend ways to help, like medication for nausea or diarrhea and moisturizing creams for rash.

It can. In studies, some people taking Koselugo had reduced heart function. Heart scans called echocardiograms showed that their heart wasn’t pumping as well. This problem usually only shows up on the scans. So your care team will do these tests regularly during treatment. This helps them monitor your heart as you take the medication. But tell your care team right away if you feel your heart beating fast, have swelling in the feet or ankles, have trouble breathing, or feel tired often. These could be signs of heart problems.

Talk to your care team before taking any vitamins or supplements. Koselugo capsules contain vitamin E. Taking more vitamin E than the recommended daily amount can raise the risk of bleeding. Ask a healthcare professional or pharmacist to check if a supplement has vitamin E and if it’s safe for you.

Yes. If you can become pregnant, or get someone pregnant, talk to your NF1 care team. You should use effective birth control while taking Koselugo and for 1 week after stopping the medication. This is important because Koselugo can harm an unborn baby. Your care team can talk about birth control options. Let your care team know right away if you or your partner gets pregnant during treatment.

If you have a baby and want to breastfeed, tell your NF1 care team. It’s not known if Koselugo passes into breast milk. But if it does, it could cause side effects in the baby. Because of this risk, avoid breastfeeding while taking Koselugo and for 1 week after the last dose. Ask your NF1 care team about safe ways for feeding.

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Risks and warnings for Koselugo (selumetinib)

Koselugo (selumetinib) can cause some serious health issues. This risk may be even higher for certain groups. If this worries you, talk to your doctor or pharmacist about other options.

Heart problems

Koselugo (selumetinib) can affect how well the heart pumps blood. In studies, some people had lower heart function, which was found on heart ultrasounds (echocardiograms). This has happened during the first year of treatment and got better a few months later.

Before starting Koselugo (selumetinib), you'll need an echocardiogram to check how well your heart is working. During treatment, you'll also have regular heart scans. In some cases, you might need a different kind of heart scan called a cardiac MRI.

If any signs of heart problems show up on your scans, your NF1 specialist will probably have you stop Koselugo (selumetinib) until your heart improves. Then, you might be able to restart the medication at a lower dose. If the heart problem is serious, the specialist might stop treatment completely.

Tell your care team right away if you have any symptoms of heart problems. Look out for cough or wheezing that doesn’t go away, shortness of breath, swelling of your ankles or feet, tiredness, or a fast heart rate.

Eye problems

Koselugo (selumetinib) can cause eye problems like blurry vision and sensitivity to bright light. Some eye problems can be more serious. This includes higher eye pressure, cataracts, or damage to the retina.

Before you start Koselugo (selumetinib), an eye specialist (ophthalmologist) will do a detailed eye exam. You'll also need regular eye exams during treatment.

Tell your NF1 specialist and ophthalmologist right away if there are any new or worsening changes in vision. They’ll do more eye exams to check what’s going on. If needed, the specialist might pause Koselugo (selumetinib) and restart it later at a lower dose. If the eye problem is very serious, you might need to stop the medication.

Diarrhea, nausea, vomiting, and mouth sores

Koselugo (selumetinib) can often cause nausea, vomiting, mouth sores, and diarrhea. In studies, diarrhea usually happened within the first 2 months of treatment and sometimes lasted for about 5 to 7 days.

If you have diarrhea, call your NF1 specialist right away. They can tell you how to help stop diarrhea, such as using medication like loperamide (Imodium A-D) after the first loose stool. Make sure to drink plenty of fluids to prevent dehydration.

If the side effects are severe, the specialist might have you take a break from Koselugo (selumetinib) and restart later at a lower dose. In more severe cases, the specialist might decide to stop treatment completely.

Get medical help right away if you have severe stomach pain, swelling, nausea, vomiting, constipation, diarrhea, or bloody stools. These can be signs of a serious stomach problem that needs medical attention.

Skin problems

Koselugo (selumetinib) can often cause rashes. These rashes can be acne-like, raised, or itchy. Tell your NF1 care team if you notice any new or worsening rash, peeling skin, or blisters.

Depending on the type of rash, the specialist might suggest using moisturizers or other topical medications to help. They might also lower the Koselugo (selumetinib) dose, pause treatment, or stop the medication altogether.

Higher creatine phosphokinase levels

Koselugo (selumetinib) can cause higher creatine phosphokinase (CPK) levels. This lab result can sometimes be a sign of muscle injury.

In studies, these lab changes were usually mild. But it sometimes led prescribers to lower the dose of Koselugo (selumetinib) or stop the medication. Also, most people didn’t have symptoms from higher CPK levels, but some also had muscle pain.

Your NF1 specialist will check your CPK levels with blood tests before starting Koselugo (selumetinib) and during treatment. If levels are high, they’ll try to figure out why. Also tell the specialist if you have muscle pain while taking this medication. The specialist might lower the dose, pause treatment, or stop the medication completely.

Higher vitamin E and bleeding risk (capsules only)

Koselugo (selumetinib) capsules contain vitamin E as one of the inactive ingredients. But too much vitamin E can interfere with how well your blood can clot. This can raise the risk of bleeding.

Talk to a healthcare professional before taking or giving any extra vitamin E, such as supplements. Also, tell your prescriber if you take blood thinners before starting Koselugo (selumetinib). These medications can raise the risk of bleeding even more. Your prescriber might need to monitor your bleeding risk or adjust your medications.

Koselugo (selumetinib) oral granules don’t contain vitamin E, so they don’t have this risk.

Harm to an unborn baby

Based on animal studies and the way it works, Koselugo (selumetinib) could harm an unborn baby if taken while pregnant. If you can become pregnant, or can get someone pregnant, you should use effective birth control during treatment. Continue to use birth control for 1 week after your last dose of Koselugo (selumetinib). If you or your partner gets pregnant during treatment, tell the prescriber right away.

Koselugo (selumetinib) dosage

Bottle

Dosage	Quantity	Price as low as	Price per unit
60 capsules of oral granules of 5mg	1 bottle	$4,144.80	$4,144.80
60 capsules of oral granules of 7.5mg	5 bottles	$31,008.00	$6,201.60

Typical dosage for Koselugo (selumetinib)

Your NF1 specialist will help determine your dose. It’s based on your body surface area (BSA), which takes into account your height and weight.

Capsules
- BSA of 0.55 m² to 0.69 m²: The typical dose is 20 mg by mouth in the morning and 10 mg in the evening.
- BSA of 0.7 m² or greater: The dose ranges from 20 mg to 50 mg by mouth twice a day.
Oral granules
- BSA of 0.4 m² or greater: The dose ranges from 12.5 mg to 50 mg by mouth twice a day.

The dose might be different if you have liver problems or if you take certain medications that interact with Koselugo (selumetinib).

How much does Koselugo (selumetinib) cost?

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Koselugo (brand)

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Koselugo (selumetinib) images

This medicine is White Bottle Imprinted With "Sel 10".White Sel 10 - Koselugo 10mg Capsule

References

Best studies we found

American Cancer Society. (2025). Chemotherapy.

American Cancer Society. (2025). Targeted therapy.

American Heart Association. (2025). Cardiac magnetic resonance imaging (MRI).

GoodRx Health has strict sourcing policies and relies on primary sources such as medical organizations, governmental agencies, academic institutions, and peer-reviewed scientific journals. Learn more about how we ensure our content is accurate, thorough, and unbiased by reading our editorial guidelines.

Koselugo