If you take oral medication for chronic myeloid leukemia (CML), you know it’s more complicated than just popping a pill. For most people in the chronic phase of CML, treatment doesn’t involve traditional chemotherapy. Instead, they usually take a daily pill that belongs to a class of medications called tyrosine kinase inhibitors (TKIs). Some TKIs have special instructions regarding food, such as not eating right before or after taking a dose.

Because TKIs are often taken for many years, it’s important to plan around the timing of your doses — and sometimes that means fasting (not eating for a period of time). Adjusting your meals and medication schedule can be tricky, especially over the long term. This article explains why fasting may be part of your CML treatment and offers tips to help you take your medication safely and effectively.

What Are Tyrosine Kinase Inhibitors?

Tyrosine kinase inhibitors are a group of drugs that treat chronic myeloid leukemia. CML occurs when a mutation (change) in the BCR-ABL gene — also called the Philadelphia chromosome — causes blood cells to grow and divide too fast. TKIs work by switching off the BCR-ABL signal in cancer cells, which helps prevent CML from getting worse.

Taking Tyrosine Kinase Inhibitors Properly

It’s important to take TKI therapy exactly as prescribed by your doctor to slow disease progression and keep you as healthy as possible. Specific instructions may vary by drug and dosage, but generally, you should:

• Take the exact dose your doctor prescribed.
• Take the medication at the same time every day, as instructed by your doctor.
• Never skip a dose or double up if you miss one.
• Listen carefully to your doctor about what foods, other medications, or supplements to avoid.
• Follow the directions about whether to take your pill with food or on an empty stomach.

It’s important to take TKI therapy exactly as prescribed by your doctor to slow disease progression and keep you as healthy as possible.

Why Do Some Tyrosine Kinase Inhibitors Require Fasting?

Food can affect how your body breaks down and processes a TKI. Eating before or after taking a dose may cause your body to absorb either too much or too little of the drug, which can make it less safe or effective. In some cases, taking a TKI with food, supplements, or other medication can also raise the risk of serious side effects, such as heart rhythm changes.

Fasting instructions aren’t just suggestions. They’re important rules to help your medication work properly and safely.

Which Tyrosine Kinase Inhibitors Require Fasting?

Some TKIs for CML treatment must be taken on an empty stomach. This means that you need to fast for at least two hours before and one hour after taking your medication — a total of three hours with no food or drink except water. This can be difficult if you have a busy or unpredictable schedule or also manage other health conditions. Always follow your doctor’s directions for each medication.

Medications That Require Fasting

Some types of tyrosine kinase inhibitors require fasting to work safely and effectively, including:

• Nilotinib (Tasigna) — Taken twice a day, with doses about 12 hours apart. Each dose must be on an empty stomach, within the three-hour fasting window, which adds up to six fasting hours every day.
• Asciminib (Scemblix) — Taken once or twice daily, depending on the prescribed dose, and always without food, following the same three-hour fasting rule. This medication may be used by people who’ve tried at least two other TKIs or who have chronic phase CML or a certain gene mutation.

In one study, about 30 percent of people on TKI therapy had trouble taking their medications every day as prescribed.

Medications That Don’t Require Fasting

Other TKIs can be taken with food, which may help reduce side effects. These medications include:

• Imatinib (Gleevec) — Take with a meal and a large glass of water.
• Dasatinib (Sprycel) — Take with or without food.
• Ponatinib (Iclusig) — Take with or without food.
• Bosutinib (Bosulif) — Take with food to help avoid an upset stomach.

In 2024, the U.S. Food and Drug Administration (FDA) approved Danziten, a new version of nilotinib that doesn’t require fasting. Your body absorbs it the same way, whether or not you’ve eaten, which may make it easier to fit into your daily schedule.

Does Fasting Make CML Treatment Harder?

Taking daily medication for a chronic (ongoing) condition like chronic myeloid leukemia is already a challenge. If you also have to fast for three to six hours a day and time your meals precisely, it can be even harder to stick to your treatment plan.

For example, if you take your pill first thing in the morning, you’ll need to wait at least an hour for breakfast. If you take it before bed, you must make sure you finish dinner at least two hours earlier. This strict scheduling can be frustrating or overwhelming, especially when you’re already experiencing the stress of living with a chronic condition.

If you’re having trouble sticking with your current TKI treatment, talk to your doctor about other options.

You may need to skip family dinners or avoid food at social gatherings, which can feel isolating. Fasting can also cause side effects such as tiredness or low blood glucose (blood sugar) levels. “Everyone kept telling me that they’re tired on cancer meds, but I was so completely exhausted from fasting all the time,” one MyLeukemiaTeam member shared. “I just couldn’t live my life.”

Support from loved ones can help, reported another member: “My wife ensures our meals are healthy and at the same time every night after I take my meds.”

What the Research Shows

Some researchers have looked at how fasting and other treatment challenges affect people with CML. In one study, about 30 percent of people taking TKIs reported having trouble taking their medication every day. Dietary restrictions were among the reasons for missed doses and adherence difficulties.

A 2011 study showed that people taking the original form of nilotinib were most likely to report trouble sticking to their medication schedule compared with people taking other TKIs. Nearly 60 percent of participants on nilotinib said the fasting requirement made it harder.

How To Stay on Track With Tyrosine Kinase Inhibitors

If you’re on medication that requires fasting, don’t be discouraged — you’re not alone. Many people have found practical ways to stick to their treatment plan. Here are some tips that might help you stay consistent.

Follow a Daily Routine

Set consistent times to take your medication. For example, taking your first dose in the morning may work well since you’ve already fasted overnight. Your second dose could be timed an hour before dinner, allowing you to eat with your family, especially if you usually dine later in the evening.

Plan Meals in Advance

Build your meals around your TKI schedule. Preparing dishes in advance can help you stick to your fasting window. You could also use the one-hour wait after taking your pill to cook dinner. Knowing when and what you’ll eat may make it easier to time your doses.

Make Use of Reminders

Calendars, alarms, pillboxes, apps — all can help you stay on track. These tools remove the stress of having to remember your dose yourself.

Seek Support

Fasting around your medication can be more than just a minor inconvenience. It might change how you socialize, fuel your body, or schedule your day and may even affect your quality of life.

If you’re having trouble staying consistent, talk to your hematology/oncology doctor. Discussing your challenges with treatment can spark important conversations about whether you’re on the right treatment plan for your lifestyle. They may adjust your dose or recommend a different TKI that doesn’t require fasting.

“Since we have to be on these meds for potentially many years with CML, it’s worth it to find one that’s livable,” one MyLeukemiaTeam member noted. Reaching out for support from your healthcare team and others with CML can help you find a plan that works for your life.

Talk With Others Who Understand

On MyLeukemiaTeam, the social network for people with leukemia and their loved ones, more than 21,000 members come together to ask questions, give advice, and share their stories with others who can relate to life with leukemia.

Did your doctor tell you to fast while taking your CML treatment? How has fasting affected your ability to stick with your treatment regimen? Share your experience in the comments below, or start a conversation by posting on your Activities page.