Many people have heard of vitamin B-12 injections and wonder if they are a worthwhile way of fending off fatigue.

My answer: Yes. For years, both holistic and conventional medical doctors have been prescribing vitamin B-12, also known as the energy vitamin, to patients with otherwise unexplained low energy. Vitamin B-12 is essential to the body’s production of red blood cells, immune system function and nervous system function.

Receiving the vitamin via injection ensures that it is quickly disseminated into the body, bypassing the digestive tract. These injections are typically given in a doctor’s office—or the patient can do it at home. The injections can be given in the buttock, thigh or arm.

Who it is for: Vitamin B-12 injections seem to work best for patients who have had chronic fatigue for at least several weeks and those who have fatigue from extreme stress. They also help patients with pernicious anemia, a condition in which vitamin B-12 cannot be absorbed properly… malabsorption problems, due to a digestive disorder, such as Crohn’s or celiac disease… and chronic trigeminal neuralgia, a painful condition that affects one of the nerves in the head.

Because people lose the ability to absorb vitamin B-12 as they age, about 20% of those over age 60 are deficient in it. Vitamin B-12 injections seem to help patients whether or not they have low blood levels of vitamin B-12 (the blood test is not always able to pick up mild deficiencies).

Effectiveness: In one landmark study published in British Journal of Nutrition several decades ago, researchers found that a vitamin B-12 injection gave people suffering from fatigue enhanced mood and well-being that lasted for several weeks after the injection was given. Typical regimen: My patients begin with an injection of 2,500 micrograms (mcg) of vitamin B-12 twice a week for four weeks and then once weekly for four weeks. After that, they receive the injection every few weeks or once a month. Even though the effects of the injections last for a while, I find that patients do best with repeated dosing.

Note: For a stronger effect, vitamin B-12 can be combined with other B vitamins in the same injection. Rare side effects may include diarrhea and nausea. Look for a holistic physician who provides these injections. Most charge about $25 to $50 per injection.