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Why Do Medical Doctors Not Want to Give B12 Shots?

author image Maria Warren, R.N.
A registered nurse, Maria Warren has worked as a professional health writer since 2006. She holds a Bachelor of Science in nursing from Salem State College and a Master of Public Health in nutrition from Tufts University. Warren is currently working toward a nurse practitioner license.
Why Do Medical Doctors Not Want to Give B12 Shots?
Avoid receiving vitamin B-12 shots if you are allergic to any ingredients in the vitamin supplements. Photo Credit: IPGGutenbergUKLtd/iStock/Getty Images

Vitamin B-12 helps maintain the health of your metabolism, red blood cells and nerves. When you have a vitamin B-12 deficiency, your doctor might prescribe vitamin B-12 shots, especially if you have an intestinal disorder that prevents the proper absorption of the vitamin. Your doctor might avoid giving you vitamin B-12 shots if you have allergies or certain medical conditions.

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If you are allergic to cobalamin, cobalt or any ingredients in vitamin B-12 shots, inform your doctor before the vitamin is prescribed. Your doctor most likely will avoid prescribing vitamin B-12 shots to prevent a severe life-threatening allergic reaction. Seek immediate medical attention if you develop symptoms of an allergic reaction while on vitamin B-12 therapy, including breathing problems, wheezing, shortness of breath, hives, or swelling of the face, tongue and throat.

Leber's Disease

Your doctor might avoid prescribing vitamin B-12 shots if you have Leber's disease, an inherited eye disorder that causes damage to nerves in the eye, according to If you take vitamin B-12 when you have Leber's disease, you might develop permanent optic nerve damage and blindness. Avoid taking OTC vitamin B-12 without consulting your doctor.

Polycythemia Vera

Your doctor also might avoid prescribing vitamin B-12 shots if you have a blood disorder called polycythemia vera, according to Polycythemia vera occurs when there is an increased production of red blood cells in your body, which leads to increased blood thickness. Vitamin B-12 might worsen polycythemia vera because it stimulates production of red blood cells.


Vitamin B-12 injections are available as a liquid that usually is injected into deep muscles in your body. The shots usually are administered at the doctor's office. If B-12 deficiency is severe, you will receive B-12 shots once a day for six to seven days. When you begin to improve, the shots might be administered every two weeks or once a month. Attend all your doctor's appointments to receive vitamin B-12 shots to prevent developing complications such as permanent spinal cord damage.

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