If you have ever taken a medicine that didn't work, you may have wondered why that happens sometimes. There are several possibilities:

  • It's the wrong medication for your condition.

  • Your condition will not respond to any medication — that is, there is no known effective medication therapy for your particular medical problem.

  • Your problem needs a different dose of the medication or a longer duration of treatment.

  • The lack of effect was a normal physiological response for you.

One other reason I've often heard from patients is that a medication does not work well because they have become "used to it" or "immune to it." Can you really become immune to a medication or is that a medical myth? The answer depends in part on how you define "immune," but, for the most part, it is a myth. Then again, as with most myths, there is some element of truth to it.

Rare, But True

Though rare, there are clearly times when a person takes a medication and his or her immune system responds to it by making antibodies. These antibodies can then cancel the effects of the medication. The person has truly become "immune" to the medicine, and continued treatment is unlikely to accomplish much (and may even be harmful). Such is the case for the occasional patient taking infliximab (brand-name Remicade). This intravenous medication is injected every one to two months for rheumatoid arthritis that has not responded well to other medicines.

Because infliximab itself is a protein that is created in part from a mouse, there was concern during its development that the immune system would see it as a "foreign" invader and create antibodies that would attack it (so-called "neutralizing" antibodies). This process could eliminate its benefit. In fact, for this reason an additional immune-suppressing medication, methotrexate, is routinely given along with infliximab to people with rheumatoid arthritis. There are other, though relatively few, examples of this phenomenon, especially with agents that are derived from animal sources.