Mavenclad Side Effects: What MS Patients Need to Know

Starting a new MS medication comes with questions — and concerns about side effects are often at the top of the list. If your neurologist has prescribed Mavenclad (cladribine), you’re probably wondering what to expect.

The good news? Most patients tolerate Mavenclad well, and many side effects are mild and manageable. But being informed helps you prepare, recognize warning signs, and communicate effectively with your healthcare team.

This guide covers everything MS patients need to know about Mavenclad side effects — from the most common symptoms to serious warnings that require immediate attention.

“Knowledge is power when it comes to managing your MS treatment. When patients understand what side effects might occur and what to watch for, they feel more confident and in control of their care.”
— Julia Kravtsova, PharmD, Head Patient Navigator at QuickRx

Understanding How Mavenclad Works (And Why Side Effects Occur)

To understand Mavenclad’s side effects, it helps to know how the medication works.

Mavenclad (cladribine) is an oral disease-modifying therapy for relapsing forms of multiple sclerosis. According to the National MS Society, it works by selectively targeting and temporarily reducing certain immune cells — specifically B and T lymphocytes — that are believed to play a role in the MS disease process.

Because Mavenclad affects the immune system, many of its side effects are related to:

• Lowered lymphocyte counts (which is expected and monitored)
• Increased susceptibility to infections while the immune system is suppressed
• The body’s response to immune cell reduction

Unlike medications you take continuously, Mavenclad is taken for just 20 days total over two years — about 4-5 days per treatment week, with two treatment weeks per year. This short-course dosing means side effects are typically most noticeable during and shortly after treatment periods.

Common Mavenclad Side Effects

The following side effects are the most frequently reported by MS patients taking Mavenclad, according to Cleveland Clinic. While they can be uncomfortable, they’re generally manageable and often improve over time.

Upper Respiratory Tract Infections

How common: Very common (affects more than 1 in 10 patients)

Symptoms similar to the common cold — runny nose, sore throat, cough, congestion — are the most frequently reported side effect. This makes sense given Mavenclad’s effect on immune cells.

Management tips:

• Practice good hand hygiene
• Avoid close contact with sick individuals during treatment periods
• Stay up to date on recommended vaccinations (before starting treatment)
• Contact your doctor if symptoms are severe or don’t improve

Headache

How common: Very common

Headaches are reported frequently during Mavenclad treatment. They’re usually mild to moderate.

Management tips:

• Stay well-hydrated
• Rest in a quiet, dark room if needed
• Ask your doctor about appropriate over-the-counter pain relievers
• Track headache frequency and severity to discuss with your care team

Lymphopenia (Low Lymphocyte Count)

How common: Very common — this is expected with Mavenclad

Reduced lymphocyte counts are not just a side effect — they’re part of how Mavenclad works. Your healthcare team will monitor your blood counts before, during, and after treatment.

What to know:

• Blood tests are required before starting each treatment course
• Treatment may be delayed if lymphocyte counts are too low
• Counts typically recover gradually over several months
• You may be more susceptible to infections while counts are low

Nausea and Upset Stomach

How common: Common

Some patients experience gastrointestinal symptoms during treatment weeks.

Management tips:

• Take Mavenclad with or without food (follow your doctor’s instructions)
• Eat smaller, more frequent meals
• Avoid spicy or greasy foods during treatment days
• Stay hydrated

Back Pain and Joint Pain

How common: Common

Musculoskeletal discomfort, including back pain and joint pain, has been reported.

Management tips:

• Gentle stretching and movement can help
• Apply heat or cold as comfortable
• Ask your doctor about appropriate pain relief options

Trouble Sleeping (Insomnia)

How common: Common

Some patients report difficulty sleeping during treatment periods.

Management tips:

• Maintain a consistent sleep schedule
• Limit caffeine, especially in the afternoon and evening
• Create a relaxing bedtime routine
• Discuss persistent sleep issues with your doctor

Hair Thinning

How common: Common

Some patients notice hair thinning or increased hair loss during treatment. This is usually temporary.

Serious Side Effects & Warnings

While most patients tolerate Mavenclad well, there are serious side effects that require awareness and monitoring. According to WebMD, your healthcare team will screen for risk factors and monitor you throughout treatment.

Serious Infections

Because Mavenclad reduces immune cells, serious and potentially life-threatening infections can occur. These include:

• Herpes zoster (shingles) — Patients with low lymphocyte counts are at increased risk
• Tuberculosis (TB) — Screening is required before starting treatment
• Hepatitis B reactivation — Screening is required before treatment
• Progressive multifocal leukoencephalopathy (PML) — A rare but serious brain infection
• Opportunistic infections — Including fungal infections

Risk reduction: Your doctor will screen for infections before treatment, may recommend vaccinations, and will monitor you during and after treatment.

Liver Problems (Hepatotoxicity)

Mavenclad can cause liver injury. Symptoms may include:

• Yellowing of the skin or eyes (jaundice)
• Dark urine
• Severe nausea or vomiting
• Upper right abdominal pain

Monitoring: Liver function tests are required before treatment and as needed during treatment.

Increased Cancer Risk

The prescribing information includes a warning about potential increased risk of malignancies (cancers). Your healthcare provider will:

• Review your cancer history before prescribing
• Recommend appropriate cancer screenings
• Monitor for signs of malignancy during and after treatment

Patients with active cancer should not take Mavenclad.

Pregnancy Risks

Mavenclad can cause serious harm to an unborn baby. Important requirements:

• Pregnancy testing is required before each treatment course
• Women must use effective contraception during treatment and for at least 6 months after the last dose
• Men must use contraception during treatment and for at least 6 months after the last dose
• Do not breastfeed during treatment and for 1 week after the last dose

Bone Marrow Suppression

In addition to lymphopenia, Mavenclad can affect other blood cell counts:

• Neutropenia (low neutrophils) — increases infection risk
• Anemia (low red blood cells) — can cause fatigue
• Thrombocytopenia (low platelets) — increases bleeding risk

Monitoring: Complete blood counts are monitored before and during treatment.

Cardiac Effects

Heart failure has been reported in patients receiving injectable cladribine for cancer treatment. While the oral MS formulation is different, cardiac function should be monitored in patients with heart conditions.

Managing Mavenclad Side Effects: Practical Tips

Being prepared can make a significant difference in how you experience Mavenclad treatment. Organizations like MS Focus emphasize the importance of patient education and preparation. Here are practical strategies from our specialty pharmacy team:

Before Treatment

• Complete all required screenings — Blood tests, TB screening, hepatitis screening, pregnancy testing
• Update vaccinations — Live vaccines should be completed at least 4-6 weeks before starting
• Stock up on supplies — Have throat lozenges, tissues, acetaminophen (if approved by your doctor), and comfort items ready
• Plan your schedule — Some patients prefer to start treatment before a weekend in case they need rest

During Treatment

• Stay hydrated — Drink plenty of water
• Rest as needed — Listen to your body
• Track symptoms — Keep a simple log of any side effects, their severity, and duration
• Avoid sick contacts — Your immune system is working hard
• Handle tablets carefully — Use dry hands, take immediately after removing from packaging

After Treatment

• Continue monitoring — Keep all follow-up appointments and lab work
• Report new symptoms — Even weeks after treatment, let your doctor know about concerning changes
• Practice infection prevention — Your lymphocyte counts may stay low for several months

“We always tell patients: you’re not alone in this. Our team is available to answer questions, help manage side effects, and coordinate with your neurologist. That support makes a real difference.”
— Julia Kravtsova, PharmD

Required Monitoring & Blood Tests

Regular monitoring is essential for safe Mavenclad treatment. According to Drugs.com, here’s what to expect:

Before Starting Treatment

• Complete blood count (CBC) with differential
• Lymphocyte count (must be within normal range)
• TB screening
• Hepatitis B and C screening
• HIV screening
• Pregnancy test (for women of childbearing potential)
• Liver function tests
• Varicella zoster (chickenpox) antibody testing

During and After Treatment

• Lymphocyte counts at 2 and 6 months after each treatment course
• Additional blood tests as directed by your healthcare provider
• Monitoring for signs of infection
• Cancer screening as recommended

Important: Treatment for Year 2 can only begin if lymphocyte counts have recovered to acceptable levels. Your neurologist may delay treatment if counts are too low.

When to Call Your Doctor Immediately

Contact your healthcare provider right away if you experience:

When in doubt, call. It’s always better to check in with your healthcare team than to wait and worry.

Don’t Let Cost Concerns Add to Your Stress

Managing side effects is easier when you’re not also worrying about how to afford your medication. Many MS patients are surprised to learn that copay assistance programs can reduce their Mavenclad costs to $0.

QuickRx Specialty Pharmacy helps patients access:

• Manufacturer copay cards (for commercially insured patients)
• Foundation grants (for Medicare patients)
• Patient assistance programs (for uninsured/underinsured patients)

We handle all the paperwork and enrollment — at no cost to you.

“Worrying about medication costs shouldn’t be another burden on top of managing MS. We take care of the financial side so patients can focus on their health and their treatment.”
— Julia Kravtsova, PharmD

Frequently Asked Questions About Mavenclad Side Effects

1. How long do Mavenclad side effects last?

Most common side effects like headache and nausea occur during treatment weeks and resolve within days. Lymphopenia (low lymphocyte counts) is expected to persist for several months as your immune system gradually recovers. Your doctor will monitor your blood counts and let you know when they’ve returned to acceptable levels.

2. Will I lose my hair on Mavenclad?

Hair thinning is a reported side effect, but complete hair loss is uncommon. Some patients notice increased shedding during or after treatment, which is usually temporary. If you’re concerned about hair changes, discuss them with your healthcare provider.

3. Can I take other medications while on Mavenclad?

Some medications can interact with Mavenclad or increase side effect risks. Always tell your doctor about all medications, supplements, and over-the-counter drugs you take. Avoid other immunosuppressive medications, and don’t receive live vaccines during treatment or while lymphocyte counts are low.

4. Is fatigue a side effect of Mavenclad?

While fatigue isn’t listed among the most common side effects, many MS patients experience fatigue as part of their condition. Some patients report feeling tired during treatment weeks. If you experience new or worsening fatigue, discuss it with your neurologist.

5. Can Mavenclad cause weight gain?

Weight gain is not a commonly reported side effect of Mavenclad. If you notice significant weight changes during treatment, discuss them with your healthcare provider to rule out other causes.

6. What happens if I get sick while taking Mavenclad?

Contact your doctor if you develop signs of infection (fever, chills, cough, sore throat that doesn’t improve). Because Mavenclad affects your immune system, infections need to be taken seriously and may require prompt treatment. Don’t wait to see if symptoms improve on their own.

7. Can I drink alcohol while taking Mavenclad?

There’s no specific prohibition against alcohol with Mavenclad, but both alcohol and Mavenclad can affect the liver. Ask your doctor about alcohol consumption, especially if you have any liver concerns. Moderation is generally advisable.

8. Are Mavenclad side effects worse than other MS medications?

Side effect profiles vary between MS medications. Mavenclad has a unique dosing schedule (20 days over 2 years) compared to daily pills or monthly infusions, which affects when and how side effects occur. Some patients prefer Mavenclad’s short treatment courses. Discuss the pros and cons of different options with your neurologist.

9. Should I be worried about the cancer warning?

The cancer warning reflects findings in clinical data that require disclosure. Your doctor will evaluate your individual risk factors, review your medical history, and recommend appropriate cancer screenings. Many patients take Mavenclad safely, but this risk should be part of your informed decision-making with your healthcare team.

10. How does QuickRx help patients manage side effects?

QuickRx provides comprehensive support for Mavenclad patients, including medication counseling, refill coordination timed to your treatment schedule, and 24/7 pharmacist access for questions. We also help ensure you can afford your medication through our free copay assistance enrollment services. Call (917) 830-2525 to learn more.

References

1. Cladribine (Lexi-Drugs). Lexicomp. UpToDate. Accessed December 2025.
2. U.S. Food and Drug Administration. Mavenclad (cladribine) Prescribing Information. EMD Serono, Inc.
3. National Institute of Neurological Disorders and Stroke. Multiple Sclerosis Information. Accessed December 2025.
4. National Multiple Sclerosis Society. Mavenclad Medication Information. Accessed December 2025.
5. Cleveland Clinic. Cladribine Tablets Drug Information. Accessed December 2025.
6. MedlinePlus. Cladribine Drug Information. U.S. National Library of Medicine. Accessed December 2025.
7. Mayo Clinic. Multiple Sclerosis Treatment. Accessed December 2025.
8. WebMD. Mavenclad Oral Drug Information. Accessed December 2025.
9. Drugs.com. Mavenclad Information. Accessed December 2025.