There are no known harmful effects from the strong magnetic field used for MRI. But the magnet is very powerful. The magnet may affect pacemakers, implantable cardioverter-defibrillators (ICDs), artificial limbs, and other medical devices that contain iron.

If you may have metal fragments in your eyes, an MRI can cause damage to the retina. If there is a concern about metal fragments in the eye, most MRI clinics will do X-rays of the eyes before the MRI. If metal is found on the X-ray, the MRI will not be done.

Iron pigments in tattoos or tattooed eyeliner can cause skin or eye irritation problems.

An MRI can cause a burn with some medicine patches. Be sure to tell your doctor if you are wearing a patch.

Contrast material that contains gadolinium may cause a serious problem (called nephrogenic systemic fibrosis) in people who have kidney failure.

There is a small risk of having an allergic reaction if contrast material is used during the MRI scan. Most reactions are mild and can be treated with medicine. There is also a small risk of infection at the IV site.

An MRI may be more likely than other tests to report a problem in the breast when a problem is not there (false-positive). A false-positive result may lead to more tests such as a biopsy when no serious problem is really present. So MRI is not used as a screening test for women at low or average risk for breast cancer.