Side Effects: Headache, nausea, vomiting, diarrhea, loss of appetite, skin rash, hot flushes

How to use: IM- 250-1,000 mcg on alternate days for 1-2 week, then 250 mcg weekly. Maintenance: 1,000-mcg monthly. It comes as a solution (liquid) to be injected into the muscle or under the skin, without food.

How it works: It is an essential nutrient that helps the body make healthy red blood and nerve cells.