Ocrevus (Ocrelizumab) Side Effects

Infusion reactions, infections, and concerns about rare risks like progressive multifocal leukoencephalopathy (PML)—these are the side effects most patients want to understand before starting Ocrevus (ocrelizumab).

If your neurologist has recommended this therapy for relapsing forms of multiple sclerosis (MS) or primary progressive MS, knowing what to expect and how to respond makes the whole process significantly more manageable.

Here’s a closer look at the Ocrevus (ocrelizumab) side effects by type, timing, and severity, so you can feel prepared going in. If you’re exploring specialty infusion support for the first time, understanding your medication is a strong place to start.

How Ocrevus (Ocrelizumab) Affects the Immune System

Ocrevus (ocrelizumab) works by targeting CD20-positive B cells, a type of white blood cell that contributes to the nerve inflammation seen in multiple sclerosis. The medication signals the body to clear these cells, which helps slow disease progression.

That reduction in B cells is what makes ocrelizumab effective—and it’s also what creates the potential for certain side effects. With fewer B cells circulating, the immune system becomes less equipped to fight off some infections, which is why close monitoring is a standard part of treatment.

Acelpa Health and its affiliated specialty pharmacies—California Specialty Pharmacy (CSP), ContinuumRx (CRx), Hawaii Specialty Pharmacy (HSP), Continuum Health (CH), and Integrated Care Systems (ICS)—support patients on a wide range of biologic and biosimilar infusion therapies, coordinating the full logistics of treatment from benefits verification to infusion scheduling.

Infusion Reactions

Infusion reactions are the most immediate concern with Ocrevus (ocrelizumab). Most patients experience at least some mild symptoms during their first few treatments, and care teams give premedications, typically corticosteroids and antihistamines (diphenhydramine), before each session to reduce severity. Reactions generally become less intense over time.

Skin, Respiratory, and Cardiovascular Reactions

Skin reactions are among the most noticeable. Itching, hives, or a rash can appear during the infusion, along with flushed skin—especially on the face and neck. Respiratory symptoms like throat irritation, a scratchy sensation, or mild shortness of breath are also common. Some patients experience heart rate changes, including a faster or slower pulse than normal, or low blood pressure.

These reactions are exactly why infusion teams monitor patients closely throughout the session. If any of these symptoms appear, alerting the team right away allows them to slow the infusion rate or take other steps to help the body adjust.

Headache, Fever, Dizziness, and Nausea

Headaches are also one of the most frequently reported symptoms during and after an infusion, ranging from mild pressure to more intense throbbing. Staying well hydrated before appointments can help reduce the severity.

Fever, chills, dizziness, and nausea often accompany these reactions and typically resolve within a day or two.

If fever persists beyond 24 hours or climbs above 100.4°F, contact your provider to rule out an infection. That threshold is an important distinction between a normal reaction and something that needs evaluation.

When to Alert the Infusion Team

Mild symptoms during infusion are expected and manageable. More urgent signs need immediate attention:

• Difficulty breathing or chest tightness
• Swelling of the face, lips, or throat
• Severe hives or sudden dizziness
• Rapid heartbeat with lightheadedness

These can signal a more serious allergic response. Tell your infusion team right away—they are equipped to respond quickly and safely.

Infection Risks

Because Ocrevus (ocrelizumab) suppresses B-cell activity, the immune system becomes more susceptible to certain infections throughout the course of treatment, not just immediately after an infusion. Knowing which infections to watch for helps patients respond quickly and get treatment early.

Upper Respiratory and Urinary Infections

Upper respiratory infections—including colds, sinusitis, and bronchitis—are the most commonly reported infections in Ocrevus (ocrelizumab) clinical trials. While these are often mild and treatable, they should be reported promptly (and treated) rather than waiting out.

Signs to watch for include a persistent cough, worsening sinus congestion, painful or frequent urination, and fever. Monitoring for infections throughout treatment is an important component of Ocrevus management.

Herpes and Shingles Virus Reactivation

Herpes virus reactivation is a specific risk with ocrelizumab. This can include cold sores, genital herpes outbreaks, or shingles (herpes zoster). Anyone with a history of herpes infections should discuss this with their provider before starting Ocrevus (ocrelizumab), as preventive antiviral medication may be recommended.

Watch for tingling, burning, or blisters on the skin and report these promptly. Shingles can cause significant discomfort and complications if not treated early, and anyone with a history of chickenpox is at risk.

Vaccine Planning Before Starting Ocrevus (Ocrelizumab)

Getting the right vaccines before beginning Ocrevus (ocrelizumab) is one of the most effective ways to reduce infection risk during treatment. Live vaccines cannot be given while on Ocrevus (ocrelizumab) or until B cells recover, and non-live vaccines may be less effective while you’re on Ocrevus.

The MS Trust advises completing live vaccines at least four weeks before the first infusion, and non-live vaccines at least two weeks before. Options to discuss with your provider include shingles, influenza, and pneumococcal vaccines.

Rare but Serious Complications

While uncommon, several serious side effects are associated with Ocrevus (ocrelizumab). Knowing the warning signs helps patients catch problems early when treatment is most effective.

Progressive Multifocal Leukoencephalopathy (PML)

PML is a rare but potentially life-threatening brain infection caused by the JC virus. This virus lives dormant in many people without causing harm. But in people with weakened immune systems, it can activate and damage brain tissue. PML has been reported in patients taking ocrelizumab.

Because PML symptoms can resemble MS symptoms, it can be difficult to identify. Contact your provider immediately if you notice:

• New or worsening weakness on one side of the body
• Vision changes or eye pain
• Sudden confusion or personality changes
• Problems with coordination or speech

Hepatitis B Virus Reactivation

Providers test for hepatitis B before starting Ocrevus (ocrelizumab) because the medication can cause the virus to reactivate in carriers, potentially causing serious liver damage. If testing comes back positive, treatment may still be possible with careful monitoring and antiviral medication.

Symptoms of hepatitis B reactivation include yellowing of the skin or eyes, dark urine, and abdominal pain. Regular liver function tests help catch reactivation before it becomes severe.

Cancer Risk Monitoring

Clinical trials noted a slightly higher rate of breast cancer in patients receiving ocrelizumab compared to placebo. The overall risk remains low, and research into the long-term relationship between Ocrevus (ocrelizumab) and cancer risk is ongoing.

Staying up to date with age-appropriate screenings and reporting any new or unexplained physical changes to your provider is an important part of ongoing Ocrevus care.

Managing Ocrevus (Ocrelizumab) Treatment Day to Day

A few practical habits make the treatment experience considerably more manageable over time:

• Before infusion: eat a light meal, hydrate well, and wear loose, comfortable clothing with sleeves that roll up easily. Bring items to help pass the time during a several-hour session.
• During infusion: communicate with the care team about any symptoms as they arise. Don’t wait until something worsens.
• Between infusions: keep a simple symptom diary noting infections, fatigue changes, or neurological shifts. This information helps the team spot patterns and adjust the care plan if needed.
• Contact your provider promptly if fever exceeds 100.4°F, any new neurological symptoms appear, or signs of infection don’t resolve on their own.

Regular lab work—including immunoglobulin levels, liver function, and blood counts—is a standard part of Ocrevus (ocrelizumab) care. As treatment continues over multiple cycles, immunoglobulin levels may gradually decrease, which can increase infection risk.

If you have any questions about coordinating labs, scheduling, or managing ongoing therapy, your CSP care team can guide you through your understanding of Ocrevus and other specialty infusion therapies.

Moving Forward with Ocrevus (Ocrelizumab) Treatment

Managing Ocrevus (ocrelizumab) side effects becomes significantly more straightforward when patients know what to expect and who to call. Infusion reactions tend to ease with each cycle. Infections, when caught early, are usually treatable. And rare complications, while worth knowing about, affect a small minority of patients.

California Specialty Pharmacy supports patients through every phase of their Ocrevus treatment—from prior authorization and medication coordination to care team communication and manufacturer-sponsored and foundation financial coordination. We believe cost and stress should never stand between a patient and the care they need.

Reach out to the California Specialty Pharmacy team if you have questions or are ready to get started. We’re here to help.

Frequently Asked Questions (FAQ): 

What are the most common Ocrevus (ocrelizumab) side effects?

The most frequently reported side effects are infusion reactions, including itching, rash, flushed skin, headache, throat irritation, and nausea, followed by upper respiratory infections. Reactions are most common during the first infusion and often become milder with your next treatments. Premedication with corticosteroids and antihistamines helps reduce their severity.

How long does it take for Ocrevus (ocrelizumab) side effects to appear?

Infusion reactions typically occur during the infusion itself or within the first 24 hours. Infections can develop at any point during treatment, sometimes weeks to months after a dose. Low immunoglobulin levels tend to appear gradually after multiple doses over many months of continued therapy.

What are the long-term side effects of Ocrevus (ocrelizumab)?

Over time, risks include serious infections such as pneumonia or shingles, gradual decreases in immunoglobulin levels, hepatitis B reactivation, rare PML brain infection, and a potential signal for increased breast cancer risk. Care teams monitor labs and overall health throughout treatment to catch changes early.

What should I avoid while taking Ocrevus (ocrelizumab)?

Avoid live vaccines during treatment and until B-cell recovery. Get live vaccines at least four weeks before starting, and non-live vaccines at least two weeks before. Don’t start Ocrevus with an active infection, and minimize close contact with people who are acutely ill. Use effective contraception during treatment and for six months after the last dose.

Can Ocrevus (ocrelizumab) cause low immunoglobulin levels?

Yes. With continued treatment over multiple cycles, immunoglobulin levels—particularly IgG and IgM—can gradually decrease. Low immunoglobulins increase infection risk. Providers monitor these levels through routine lab work and will discuss management options if they drop significantly.

Is Ocrevus (ocrelizumab) safe if I have a history of infections?

This depends on the type and frequency of infections. Providers will review infection history before starting Ocrevus and may recommend additional precautions—such as antiviral prophylaxis for herpes or closer monitoring for specific infection types. In most cases, a thorough history helps the care team create a plan that supports safer treatment.