When the immune system produces antibodies to infused factor replacement therapy it is known as an inhibitor, a complication that makes treatment in a hemophilia patient very challenging.

Having hemophilia and other bleeding disorders can mean coping with various complications that can arise throughout the patient’s lifetime. Some patients have more severe complications, while others have only mild complications. Some of the complications that can occur in patients with hemophilia are discussed below.


Some patients develop an immune response to the medications used to treat hemophilia. The immune system is the primary defense system of the body against disease and foreign agents. For these patients, the immune system produces antibodies that “inhibit” clot formation by destroying the clotting factor before it has a chance to stop the bleeding. The reason for a patient developing inhibitors is still not entirely clear. The presence of an inhibitor makes treating bleeds more difficult. Standard treatment does not work, and other methods to control bleeding must be used. Here you’ll find information for both patients and providers on how inhibitors are diagnosed, treated and managed.

Unusual Bleeds

Bleeds beneath the skin can cause large bruises that take time to heal. Bleeding in certain areas—the eye, head, brain, throat or gastrointestinal tract—can be life threatening and require immediate attention.

Joint Damage

Bleeding into joints and muscles can cause swelling, pain and immobility. Bleeds in muscles can cause permanent nerve damage when the trapped blood or swollen muscles put pressure on a nerve. Some sites can become target joints, where repeat bleeds damage the lining of the joint, called the synovium. Synovitis is a condition where chronic inflammation in the joint from recurrent bleeds has thickened the synovium, reducing the joint space and limiting movement. The bones can then become arthritic and develop cysts. Eventually, there may be so much damage that a joint replacement or fusion may be needed.

Copyright National Hemophilia Foundation

Last Updated May 2022

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