Do biologics have bad side effects? An in-depth look

October 9, 2025 •

4 min read

A 2011 Cochrane review found that people on biologics were slightly more likely to experience serious infections compared to those on a placebo, highlighting the reality that the question, "Do biologics have bad side effects?", requires a nuanced answer. These advanced medications, derived from living organisms, target specific parts of the immune system, leading to both significant therapeutic benefits and potential complications.

Quick Summary

Biologic medications can cause side effects ranging from common injection site reactions to rare but serious health issues like infections or heart problems. The overall risk profile is individualized based on the specific drug, patient health history, and underlying condition, requiring careful discussion with a healthcare provider.

Key Points

Increased Infection Risk: Biologics can suppress the immune system, raising susceptibility to common and serious infections, including the reactivation of latent TB or hepatitis B.
Injection and Infusion Reactions: Mild reactions like redness and swelling are common at injection sites, while IV infusions can cause systemic symptoms like fever and chills.
Rare but Serious Complications: Rare side effects include neurological disorders (like demyelinating disease), worsened congestive heart failure, and a slightly increased risk of certain cancers.
Individualized Risk Assessment: The likelihood and type of side effect vary significantly based on the specific biologic, duration of use, and the patient's unique medical history.
Balancing Benefits and Risks: For many patients with severe autoimmune disease, the profound benefits of biologics in controlling symptoms and preventing joint damage are considered to outweigh the potential risks.
Proactive Monitoring: Regular screening before starting treatment and close, ongoing communication with a healthcare provider are essential for managing potential adverse effects safely.
Targeted Action: Unlike traditional DMARDs that broadly suppress the immune system, biologics offer more targeted action, which can result in a different side effect profile, often with fewer systemic issues.

Biologic medications have revolutionized the treatment of numerous inflammatory and autoimmune conditions, including rheumatoid arthritis, psoriasis, and Crohn's disease. By targeting specific proteins or immune cells, they offer more focused and effective therapy than traditional, broad-acting immunosuppressants. However, because they modulate the immune system, side effects are a genuine concern for many patients. While mild reactions are common, more serious complications can occur, underscoring the importance of understanding and monitoring these risks.

Common Side Effects of Biologics

Many people on biologic therapy experience side effects, particularly when first starting treatment. The nature of these reactions can differ depending on the specific drug and its administration method (injection or infusion).

Injection and Infusion Reactions

Injection site reactions: For medications administered via a subcutaneous injection, such as adalimumab (Humira) or etanercept (Enbrel), localized symptoms are common. Patients may experience redness, pain, swelling, bruising, or itching at the injection site. These reactions are usually mild and tend to resolve within a few days.
Infusion reactions: Biologics given intravenously, like infliximab (Remicade), can sometimes cause reactions during or shortly after the infusion. Symptoms may include headaches, fever, chills, flushing, itching, or a rash. In some cases, pre-medication with antihistamines or other medications can help prevent these reactions.

Systemic Side Effects

Beyond administration-related issues, other common side effects can occur as the body adjusts to the medication.

Flu-like symptoms: Some patients experience fatigue, headache, fever, and muscle aches, especially during the initial phase of treatment.
Gastrointestinal issues: Nausea, vomiting, diarrhea, or stomach pain can also occur.
Increased susceptibility to common infections: Because many biologics suppress the immune system, patients may be more prone to common infections like colds, sinus infections, or urinary tract infections.

Serious and Rare Complications

While the risk of severe side effects is low for most patients, it is important to be aware of the potential for more significant complications.

Increased Risk of Serious Infections

One of the most significant concerns is an increased risk of serious or opportunistic infections. Biologics suppress parts of the immune system that would normally fight off infectious agents, including bacteria, viruses, and fungi.

Reactivation of latent infections: Before starting many biologics, particularly TNF inhibitors, doctors screen patients for latent infections such as tuberculosis (TB) and hepatitis B, as the medication can cause these to reactivate.
Fungal infections: Patients can become more susceptible to invasive fungal infections, especially those living in or traveling to specific geographic regions.

Neurological and Cardiac Issues

Though rare, some biologics have been linked to neurological and cardiac complications.

Neurological disorders: Certain anti-TNF biologics have been associated with a small risk of central nervous system (CNS) disorders, including vision problems, numbness, tingling, and demyelinating conditions like multiple sclerosis.
Heart failure: For patients with existing heart problems, particularly moderate-to-severe congestive heart failure, some anti-TNF inhibitors can worsen their condition and are generally avoided.

Other Rare Effects

Lupus-like syndrome: In rare cases, patients may develop drug-induced lupus, which can manifest as a rash on the face and arms that worsens with sun exposure, accompanied by new joint and body pain.
Cancer risk: While studies have yielded mixed results, some older research and specific circumstances have linked certain biologics to a slightly increased risk of certain cancers, including lymphoma and non-melanoma skin cancer. The risk is generally considered low, but consistent monitoring is advised.

Comparison: Biologics vs. Traditional DMARDs


Feature	Biologics	Traditional DMARDs (e.g., Methotrexate)
Mechanism	Highly targeted, acting on specific immune cells or proteins.	Broad-acting immunosuppression.
Side Effects (Generally)	Fewer systemic side effects overall, as they are more targeted.	More common systemic side effects like liver abnormalities and blood count changes.
Infection Risk	Potential for higher risk of serious infections and reactivation of latent infections.	Also increases infection risk, but different profile.
Administration	Injected (subcutaneous) or infused (intravenous).	Typically oral tablets.
Specific Risks	Small risk of neurological issues, heart failure, and certain cancers.	Higher risk of liver damage and bone marrow suppression.

Managing Side Effects and Balancing Risks

Effectively managing side effects starts with proactive screening and monitoring by a healthcare provider.

Pre-treatment screening: Before starting a biologic, a doctor will screen for latent infections like TB and Hepatitis B and review overall health, including cardiac function. Vaccinations for certain infections may also be recommended.
Patient communication: Open communication with your doctor about any new or worsening symptoms is crucial. For mild injection site reactions, cold compresses or OTC antihistamines can help, but more severe or persistent symptoms should be reported.
Personalized treatment: The choice of biologic and the management of its side effects are highly personalized. For some, the significant improvement in quality of life and disease management from biologics far outweighs the risks. If a particular biologic isn't tolerated, switching to another agent within the same class or a different class may be necessary.

For more information on managing conditions treated with biologics, the Arthritis Foundation offers comprehensive resources and patient guides on their website.

Conclusion

While biologics are powerful tools that have transformed the management of chronic autoimmune diseases, they are not without side effects. The risks range from common and manageable injection site reactions to rare but serious complications, including an increased susceptibility to serious infections. However, the severity and likelihood of these side effects are highly dependent on the specific medication, the patient's individual health profile, and consistent medical oversight. For many patients, the therapeutic benefits of controlling a debilitating disease significantly outweigh the potential risks. A thorough discussion with your doctor, including pre-treatment screening and ongoing monitoring, is the best way to ensure that biologic therapy is a safe and effective option for you.

Frequently Asked Questions

The most common side effects depend on the administration method. For injected biologics, pain, redness, or swelling at the injection site is very common. For infused biologics, headache, fever, and flu-like symptoms are frequently reported.

Yes, many biologics can increase the risk of infection by suppressing parts of the immune system. This includes a higher risk for both common infections like colds and more serious infections, such as the reactivation of latent tuberculosis or hepatitis B.

The data is mixed, but overall, the link between biologics and cancer risk is not strong, and any increased risk is considered very low. Some studies have suggested a slightly increased risk of certain types of cancer, like non-melanoma skin cancer or lymphoma, but more research is needed.

Individuals with a history of certain medical conditions may need to avoid biologics. This includes those with latent tuberculosis, moderate-to-severe congestive heart failure, demyelinating disease, or chronic hepatitis B.

Mild injection site reactions can often be managed with a cold compress, over-the-counter antihistamines, or steroid creams. Changing the injection site regularly can also help reduce irritation. If reactions are severe or persist, contact your healthcare provider.

No, most side effects, particularly mild ones like injection site reactions or flu-like symptoms, are temporary and may decrease or resolve over time. However, rare, serious side effects can be persistent or have lasting effects, requiring prompt medical attention.

Safety depends on the specific drug and patient. Biologics have fewer broad systemic side effects than traditional DMARDs because they are more targeted. However, they may carry a different risk profile, with a higher potential for serious infections in some cases.