Monoclonal Antibodies: What They Are, How They Work, Uses and Side Effects
Updated: 6 days ago
Written and medically reviewed by Dr. Baraa Alnahhal, MD · Last reviewed: October 2026 · How we review
Quick Answer: What are monoclonal antibodies?
Monoclonal antibodies are lab-made treatments built from many identical copies of one antibody that recognizes a single, specific target. They help the immune system fight disease or block proteins that cause it. They mainly treat cancer, autoimmune and inflammatory conditions, and are given by IV infusion or injection under the skin. Seek urgent care for any unexpected reaction. [1]
What the research says
A single injection cut RSV chest infections in healthy babies by about three-quarters. In a trial of 1,490 late-preterm and term infants, one injection of the monoclonal antibody nirsevimab before RSV season lowered medically attended RSV lower respiratory tract infection to 1.2%, compared with 5.0% on placebo — an efficacy of 74.5% over 150 days. (Hammitt et al., N Engl J Med, 2022) [3]
Migraine-prevention antibodies reduce monthly migraine days. A meta-analysis of 21 trials with 13,367 adults found that CGRP antibodies cut monthly migraine days by 1.50 days more than placebo in episodic migraine and 2.24 days more in chronic migraine; about 66% of the benefit was linked to contextual (placebo) effects. (Forbes et al., Headache, 2020) [4]
A twice-yearly injection lowered fracture risk in osteoporosis. In 7,868 postmenopausal women with osteoporosis, denosumab given under the skin every 6 months for 36 months reduced new spine fractures by 68% (2.3% vs. 7.2%) and hip fractures by 40% (0.7% vs. 1.2%) compared with placebo. (Cummings et al., N Engl J Med, 2009) [5]
Key takeaways
Monoclonal antibodies are lab-made copies of one antibody, so every copy locks onto the same target. [1]
They are used mainly for cancer, autoimmune diseases and inflammatory conditions — and also for migraine, asthma, high cholesterol, osteoporosis, eye conditions and some infections. [1]
Most are given through an IV; some are injected under the skin, sometimes at home. [1]
Because they aim at a very specific target, they may cause fewer side effects than some other treatments. [1]
Infusion reactions can happen. Call your provider or go to the emergency room for any unexpected reaction. [1]
What are monoclonal antibodies?
Monoclonal antibodies are lab-made proteins made of many identical copies (clones) of a single antibody, and every copy recognizes the same specific target. [1]
Antibodies are proteins your immune system makes to find and stick to something specific, such as a germ. If you want a refresher on how natural antibodies work, see our guide to antibodies.
The word "monoclonal" means the copies all come from one original antibody. That is the opposite of polyclonal antibodies, which are a mix of antibodies that recognize different targets.
Scientists also use monoclonal antibodies in medical research and laboratory testing, not only as treatments. [1]
How do monoclonal antibodies work?
Monoclonal antibodies work by attaching to one specific target in the body and then either helping the immune system attack it or blocking it from doing harm. [1]
What happens after the antibody attaches depends on the medicine and the disease.
What the antibody does | What that means for you |
Marks harmful cells | Flags cells so your immune system can find and destroy them |
Triggers cancer cell death | Causes some cancer cells to die |
Blocks growth signals | Stops proteins that cancer cells need to grow |
Cuts off blood supply | Blocks the growth of blood vessels that feed tumors |
Blocks inflammation | Stops proteins that drive inflammation |
Calms the immune system | Suppresses immune activity — for example, to help prevent organ transplant rejection |
Delivers treatment | Carries radiation or chemotherapy straight to a specific target |
Source: [1]
In cancer care, this targeted approach is why monoclonal antibodies are often grouped with targeted therapy and immunotherapy. You can read more in this overview of monoclonal antibodies in cancer treatment.
What conditions do monoclonal antibodies treat?
Monoclonal antibodies mainly treat cancer, autoimmune diseases and inflammatory conditions, and they are also used for a growing list of other conditions. [1]
Source: [1]
Your provider chooses a specific monoclonal antibody based on your condition and the exact target involved. For autoimmune examples, see our guides to rheumatoid arthritis and psoriasis.
How are monoclonal antibodies given?
Monoclonal antibodies are given either through an IV into a vein or as an injection under the skin (subcutaneous). [1]
IV infusion | Injection under the skin | |
How it's given | Through a vein | Under the skin (subcutaneous) |
Where | At a clinic or hospital | At a clinic, or at home once you're taught how |
Usual injection site | A vein | Usually the belly or upper thigh |
Monitoring | A provider watches you for reactions | Your care team tells you what to watch for |
How often | Depends on your condition | Depends on your condition |
Source: [1]
Most monoclonal antibodies are given by IV. During the infusion, a healthcare provider monitors you for any reaction. [1]
How often you need treatment, and for how long, depends on the condition being treated. [1]
If your treatment is an injection under the skin, your care team may teach you to give it to yourself at home. [1]
What are the benefits of monoclonal antibodies?
The main benefit of monoclonal antibodies is precision: because they attach to a very specific target, they may cause fewer side effects than some other treatments. [1]
That precision also lets them do jobs other medicines can't, such as delivering radiation or chemotherapy directly to a target. [1]
Are monoclonal antibodies the same as chemotherapy?
Monoclonal antibodies are not traditional chemotherapy. [1]
Depending on how they work, they are often called biologics, targeted therapy or immunotherapy. [1] Traditional chemotherapy is a different kind of treatment, although some monoclonal antibodies are used to carry chemotherapy straight to a specific target. [1]
What are the side effects and risks of monoclonal antibodies?
The main risks of monoclonal antibodies are infections, because some weaken the immune system, and infusion reactions, because many stimulate it. [1]
Weaker immune defenses. Some monoclonal antibodies suppress the immune system. This can make it harder for your body to fight infections. [1]
Immune reactions. Many monoclonal antibodies stimulate the immune system. This can cause infusion reactions or serious side effects, including: [1]
Allergic reactions
Anaphylaxis (a severe, life-threatening allergic reaction)
Serum sickness
What does an infusion reaction look like?
An infusion reaction to a monoclonal antibody commonly shows up as rash, fever, chills, shortness of breath, sweating, blood pressure changes or a racing heart. [1]
Sign | What you may notice |
Rash | New redness, bumps or itching on the skin |
Fever and chills | Feeling hot, then shivery |
Shortness of breath | Trouble catching your breath |
Sweating | Sudden sweating without effort |
Blood pressure changes | Your blood pressure rises or drops |
Racing heart | A fast or pounding heartbeat |
Source: [1]
Your provider may slow the infusion or lower the dose to reduce the chance of a reaction. [1]
When should you call a doctor after monoclonal antibody treatment?
You should call your healthcare provider or go to the emergency room if you have any unexpected reaction after monoclonal antibody treatment. [1]
Before your first dose, ask your provider which side effects to watch for with your specific medicine. [1] Knowing what is expected — and what isn't — helps you act quickly.
Don't wait it out. Serious reactions such as anaphylaxis can happen, so any unexpected reaction is a reason to get help right away. [1]
Conclusion
Monoclonal antibodies are lab-made copies of a single antibody that lock onto one specific target. That precision lets them mark harmful cells, block disease-driving proteins, calm an overactive immune system or deliver treatment exactly where it is needed. [1]
They are used most for cancer, autoimmune and inflammatory conditions, and increasingly for migraine, asthma, high cholesterol, osteoporosis and some infections. [1] Most are given by IV with monitoring, and some are injected under the skin at home. [1]
They are generally well targeted, but infusion reactions and infections can happen. Know the warning signs, and don't wait to get help if something feels wrong.
Your next step: If you've been offered a monoclonal antibody, write down your questions and bring them to your next appointment — what it targets, how often you'll need it, and which side effects to watch for. Then keep learning with our guides to cancer immunotherapy, CGRP migraine medicines and RSV.
FAQ
What are monoclonal antibodies?
Monoclonal antibodies are lab-made treatments made of many identical copies of one antibody that recognizes a specific target. They either help the immune system fight disease or block proteins that cause it.
What conditions are treated with monoclonal antibodies?
Monoclonal antibodies mainly treat cancer, autoimmune diseases and inflammatory conditions. They are also used for asthma, allergies, eye conditions, high cholesterol, neurological conditions, migraine, osteoporosis and some infections, such as RSV and Ebola.
How are monoclonal antibodies given?
Most monoclonal antibodies are given through an IV into a vein while a provider monitors you for reactions. Some are injected under the skin, usually in the belly or upper thigh, either at a clinic or at home after you're taught how.
Are monoclonal antibodies a type of chemotherapy?
Monoclonal antibodies are not traditional chemotherapy. Depending on how they work, they are often called biologics, targeted therapy or immunotherapy.
What are the side effects of monoclonal antibodies?
Monoclonal antibodies can cause infusion reactions and serious side effects such as allergic reactions, anaphylaxis, cytokine release syndrome and serum sickness. Some also suppress the immune system, which can make it harder to fight infections.
What are the signs of an infusion reaction?
Common signs of an infusion reaction to a monoclonal antibody are rash, fever, chills, shortness of breath, sweating, blood pressure changes and a racing heart. Your provider may slow the infusion or lower the dose to reduce reactions.
Do monoclonal antibodies weaken the immune system?
Some monoclonal antibodies suppress the immune system, which can make it harder to fight infections. Others do the opposite and stimulate the immune system to attack disease.
When should I get emergency help after monoclonal antibody treatment?
Call your healthcare provider or go to the emergency room if you have any unexpected reaction after monoclonal antibody treatment. Ask your provider beforehand which side effects to watch for.
Why do monoclonal antibody drug names end in -mab?
The ending -mab stands for monoclonal antibody. Examples include rituximab, adalimumab and pembrolizumab.
How long does a monoclonal antibody infusion take?
It depends on the medicine and the dose, and can range from under an hour to several hours. First infusions are often given more slowly so your care team can watch for a reaction.
Related Reading
Convalescent Plasma: How It Works, Uses and Effectiveness explains convalescent plasma.
Biosimilars: What They Are, Safety and How They Compare to Biologics explains biosimilar medicines.
Antibody-Drug Conjugates (ADCs): How They Work and Side Effects explains antibody-drug conjugates for cancer.
Biologics: What They Are, Types, Uses and Side Effects explains biologic medicines and how they're used.
References
Cleveland Clinic. Monoclonal Antibodies. Cleveland Clinic. Last updated December 10, 2025. https://my.clevelandclinic.org/health/treatments/22246-monoclonal-antibodies
National Cancer Institute. Monoclonal Antibodies. National Cancer Institute. Posted September 24, 2019. https://www.cancer.gov/about-cancer/treatment/types/immunotherapy/monoclonal-antibodies
Hammitt LL, Dagan R, Yuan Y, et al. Nirsevimab for Prevention of RSV in Healthy Late-Preterm and Term Infants. N Engl J Med. 2022;386(9):837-846. PMID 35235726. https://doi.org/10.1056/NEJMoa2110275
Forbes RB, McCarron M, Cardwell CR. Efficacy and Contextual (Placebo) Effects of CGRP Antibodies for Migraine: Systematic Review and Meta-analysis. Headache. 2020;60(8):1542-1557. PMID 32668023. https://doi.org/10.1111/head.13907
Cummings SR, San Martin J, McClung MR, et al. Denosumab for prevention of fractures in postmenopausal women with osteoporosis. N Engl J Med. 2009;361(8):756-765. PMID 19671655. https://doi.org/10.1056/NEJMoa0809493
Medical disclaimer
This article is for general education only and does not replace professional medical advice, diagnosis or treatment. Always talk with your healthcare provider about your own health and before starting, changing or stopping any treatment. If you think you are having a medical emergency, call your local emergency number right away.
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