Understanding Cyltezo Side Effects

Starting a new biologic medication can feel overwhelming, especially when the side effects list looks long. The good news: most people who take Cyltezo (adalimumab-dbll) tolerate it well. But knowing what's normal, what's not, and when to call your doctor can help you feel more confident about your treatment.

This guide covers the common and serious side effects of the Cyltezo Pen 40 Mg/0.4 Ml Starter Pack, drawn directly from FDA labeling.

What Is Cyltezo? (Quick Overview)

Cyltezo is an FDA-approved interchangeable biosimilar to Humira (adalimumab). It's a TNF-alpha inhibitor biologic made by Boehringer Ingelheim, used to treat autoimmune conditions including rheumatoid arthritis, psoriatic arthritis, Crohn's disease, ulcerative colitis, plaque psoriasis, hidradenitis suppurativa, ankylosing spondylitis, juvenile idiopathic arthritis, and uveitis. For a full overview, see our guide on what Cyltezo is and how it's used.

Common Side Effects

These side effects are reported frequently in clinical trials and are generally manageable. They don't always require medical attention, but let your doctor know if they persist or worsen:

• Injection site reactions — Redness, swelling, pain, or itching at the injection site. This is the most commonly reported side effect. It typically improves within a few days and tends to decrease over time as your body adjusts.
• Upper respiratory infections — Cold-like symptoms including sore throat, nasal congestion, and sinus pressure.
• Headache — Mild to moderate headaches, particularly in the first few weeks of treatment.
• Rash — Mild skin reactions that may appear anywhere on the body.
• Nausea — Usually mild and may resolve as your body adjusts.
• Back pain — Some patients report new or worsening back pain.
• Urinary tract infections — Symptoms include burning during urination, frequent urination, or cloudy urine.

Tips for Managing Injection Site Reactions

Since injection site reactions are so common, here are some practical tips:

• Let the pen reach room temperature before injecting (up to 14 days at room temperature is safe for Cyltezo)
• Rotate injection sites between your thighs and abdomen
• Apply a cold pack to the area after injecting
• The Cyltezo Pen is citrate-free with a 29-gauge needle, which many patients find less painful than older formulations

Serious Side Effects

These are less common but require immediate medical attention. Cyltezo carries FDA boxed warnings — the most serious type of safety alert — for two categories:

Boxed Warning: Serious Infections

TNF-alpha inhibitors like Cyltezo suppress part of your immune system, which increases your risk of serious infections. These can include:

• Tuberculosis (TB) — You'll be tested for TB before starting Cyltezo. Report any cough, fever, or night sweats immediately.
• Invasive fungal infections — Histoplasmosis, coccidioidomycosis, and other fungal infections, especially in certain geographic regions.
• Bacterial and viral infections — Including sepsis and opportunistic infections that can lead to hospitalization or death.

Call your doctor immediately if you develop fever, chills, persistent cough, weight loss, fatigue, or any signs of infection while taking Cyltezo.

Boxed Warning: Malignancies

Lymphoma and other cancers have been reported in children and adolescents taking TNF-alpha inhibitors. Adults may also have an increased risk of certain cancers, particularly lymphoma. Discuss your individual risk with your doctor.

Other Serious Side Effects

• Hepatitis B reactivation — If you're a carrier of hepatitis B, Cyltezo can cause the virus to become active again. You'll be tested before starting treatment.
• Heart failure — Cyltezo can worsen existing heart failure. Tell your doctor about any history of heart problems.
• Lupus-like syndrome — Symptoms include joint pain, a rash on the cheeks or arms, and shortness of breath. These usually resolve when the medication is stopped.
• Demyelinating disorders — Rarely, TNF inhibitors have been associated with conditions affecting the nervous system, including symptoms similar to multiple sclerosis.
• Cytopenias — Low blood cell counts that can cause unusual bruising, persistent bleeding, or pale skin.
• Anaphylaxis — Severe allergic reactions are rare but possible. Seek emergency care for difficulty breathing, swelling of the face or throat, or rapid heartbeat after injection.

Specific Populations

Pregnancy

Cyltezo should be used during pregnancy only if clearly needed. There is limited data on adalimumab use in pregnant women. Discuss the risks and benefits with your doctor if you're pregnant or planning to become pregnant.

Breastfeeding

Adalimumab is present in breast milk in low levels. Your doctor can help you weigh the benefits of breastfeeding against the potential risks to the infant.

Children

Cyltezo is approved for juvenile idiopathic arthritis in children ages 2 and older. The boxed warning about malignancy risk in children and adolescents is especially important to discuss with your pediatric specialist.

Older Adults

Older adults may have a higher risk of infections while on Cyltezo. Your doctor may monitor you more closely.

How to Manage Side Effects

Most common side effects of Cyltezo are manageable with a few strategies:

1. Keep a side effects journal — Track what you experience and when. This helps your doctor spot patterns and adjust your treatment if needed.
2. Don't skip doses — Inconsistent dosing can actually increase side effects. Stick to your every-other-week schedule.
3. Stay up to date on vaccines — Get your flu shot, pneumonia vaccine, and other recommended immunizations before starting Cyltezo. Avoid live vaccines while on treatment.
4. Report infections early — Even minor infections deserve a call to your doctor. Early treatment is key.
5. Get regular lab work — Your doctor will schedule blood tests to monitor for cytopenias, liver issues, and other potential problems.

For information on medications to avoid while taking Cyltezo, read our drug interactions guide.

Final Thoughts

The Cyltezo Pen 40 Mg/0.4 Ml Starter Pack has a well-characterized safety profile as an interchangeable biosimilar to Humira. Most side effects are mild — injection site reactions, upper respiratory infections, and headaches are the most common. The serious risks, while real, are manageable with proper screening, monitoring, and communication with your doctor.

If you're having trouble finding Cyltezo at your pharmacy, Medfinder can help you locate pharmacies with it in stock.