Humira Pen 40 Mg/0.4 Ml Starter Pack - Side Effects: What to Expect and When to Call Your Doctor

Understanding Humira Side Effects

If you've been prescribed Humira Pen 40 Mg/0.4 Ml Starter Pack, it's natural to wonder about side effects. Like all medications, Humira (Adalimumab) can cause side effects — some mild and manageable, others that need immediate medical attention.

This guide covers what to expect when starting Humira, which side effects are common, which are serious, and when you should contact your doctor right away.

What Is Humira?

Humira is a biologic medication made by AbbVie. It belongs to a class of drugs called TNF (Tumor Necrosis Factor) blockers. It's used to treat autoimmune conditions including rheumatoid arthritis, Crohn's disease, ulcerative colitis, plaque psoriasis, hidradenitis suppurativa, ankylosing spondylitis, psoriatic arthritis, and uveitis. For a complete overview, see our guide on what Humira is and how it's used.

Because Humira works by suppressing part of your immune system, many of its side effects are related to your body's reduced ability to fight off infections.

Common Side Effects

Most people who take Humira experience at least one of these side effects, especially during the first few weeks. These are generally mild and often improve as your body adjusts:

• Injection site reactions — redness, swelling, itching, or pain where you injected. This is the most common side effect and affects up to 20% of patients.
• Upper respiratory infections — cold-like symptoms including sore throat, sinus congestion, and runny nose
• Headache
• Rash
• Nausea
• Back pain
• Urinary tract infections (UTIs)
• Abdominal pain
• Fatigue

Injection site reactions tend to be most noticeable with your first few doses. The citrate-free formulation in the 40 mg/0.4 mL pen (which is what this starter pack contains) was specifically designed to reduce injection pain compared to the older formulation.

Serious Side Effects

Humira carries a boxed warning — the most serious type of FDA safety alert — for two major risks: serious infections and certain cancers. While these are rare, they are important to understand.

Serious Infections

Because Humira suppresses TNF-alpha, a key part of your immune defense, it increases your risk of:

• Tuberculosis (TB) — including reactivation of latent TB. This is why you'll be tested for TB before starting treatment and monitored during therapy.
• Bacterial sepsis — a life-threatening blood infection
• Invasive fungal infections — including histoplasmosis and aspergillosis
• Opportunistic infections — infections that healthy immune systems would normally fight off

Malignancies (Cancer)

• Lymphoma — slightly increased risk, particularly in children and young adults
• Hepatosplenic T-cell lymphoma (HSTCL) — a rare but often fatal type of cancer. This has occurred primarily in adolescent and young adult males with inflammatory bowel disease who were also taking Azathioprine or 6-Mercaptopurine alongside a TNF blocker.
• Other cancers — skin cancers (melanoma and non-melanoma) have been reported

Other Serious Side Effects

• Heart failure — new or worsening symptoms
• Demyelinating disorders — conditions like multiple sclerosis or Guillain-Barré syndrome
• Cytopenias — significant drops in blood cell counts (pancytopenia, aplastic anemia)
• Hepatotoxicity — liver damage or liver failure
• Lupus-like syndrome — symptoms include joint pain, chest pain, rash, and shortness of breath
• Severe allergic reactions (anaphylaxis) — rare but possible

Specific Populations

Pregnant or Breastfeeding Women

Humira is classified as Pregnancy Category B. Animal studies have not shown harm, but there are limited studies in pregnant women. Use Humira during pregnancy only if clearly needed and discussed with your doctor. The effects on breastfeeding are not fully known — talk to your doctor before nursing while on Humira.

Older Adults (65+)

Elderly patients may be at higher risk for infections while taking Humira. If you're 65 or older, your doctor may monitor you more closely.

Children

Humira is FDA-approved for several pediatric conditions (juvenile idiopathic arthritis age 2+, pediatric Crohn's disease age 6+, pediatric uveitis age 2+, pediatric ulcerative colitis age 5+). However, the boxed warning about malignancy risk specifically highlights children and adolescents.

Patients with Hepatitis B

If you carry hepatitis B, Humira can cause reactivation of the virus. You should be tested before starting treatment and monitored closely throughout therapy.

How to Manage Common Side Effects

Here are practical tips for dealing with the most frequent side effects:

Injection Site Reactions

• Let the pen reach room temperature for 15-30 minutes before injecting
• Rotate injection sites between your thigh and abdomen
• Apply a cold pack to the area before and after injection
• Don't rub the injection site afterward

Upper Respiratory Symptoms

• Stay hydrated and rest when you feel cold-like symptoms coming on
• If symptoms persist for more than a week or worsen, contact your doctor — it could be a sign of a more serious infection

General Tips

• Keep all scheduled follow-up appointments and lab work
• Get recommended vaccines before starting Humira when possible — avoid live vaccines during treatment
• Tell your doctor about any new symptoms, even if they seem minor
• Be aware of drug interactions that could increase side effects

When to Call Your Doctor Immediately

Contact your doctor or seek emergency care if you experience:

• Fever, chills, or flu-like symptoms that don't go away
• Cough that doesn't improve or produces blood
• Shortness of breath
• Signs of infection — burning with urination, skin wounds that won't heal, unusual fatigue
• Unusual bruising or bleeding
• Numbness or tingling in your hands or feet
• Vision changes
• Yellowing of skin or eyes (jaundice)
• Chest pain or swelling in legs
• Severe allergic reaction — difficulty breathing, swelling of face/throat, severe rash

Final Thoughts

Most people tolerate Humira well, and the common side effects — like injection site reactions and mild cold symptoms — tend to improve over time. But because Humira affects your immune system, staying alert to signs of serious infection or other complications is important.

The best thing you can do is maintain open communication with your doctor, keep up with regular lab work, and report any new or unusual symptoms promptly. If you're just getting started with Humira and want to learn more about the medication, read our complete guide on what Humira is and how it works. And if you need help finding it in stock, Medfinder can help you locate a pharmacy near you.