A banana bag is an intravenous nutritional supplement that commonly is prescribed to hospital patients who have nutritional deficiencies or chemical imbalances. It contains a liter of saline solution that includes a 10 milliliter ampoule of multivitamin injection (MVI); one milligram of folic acid, which is vitamin B9; 100 milligrams of thiamine, which is vitamin B1; and sometimes three grams of magnesium sulfate, depending on the circumstances and the facility where the banana bag is administered. The term “banana bag” refers to the bright yellow color of the solution, which is because the MVI contains riboflavin, which is vitamin B2.

The MVI in the solution is a balanced supplement of essential vitamins and minerals needed for normal bodily function. Folic acid, or folacin, which is found in leafy vegetables, fruits, beans, grains and nuts, is essential for the synthesis of deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), for healthy cell growth and reproduction and for the production of red blood cells. Thiamine, which can be found in meats, yeast and bran, plays a key role in the conversion of carbohydrates to energy in the body, in protein metabolism and in the function of the nerves and muscles. Magnesium sulfate, also known as Epsom salt, serves as an anticonvulsant and as an electrolyte supplement. It also is helpful in the relief of nerve pain and as a treatment for the alcohol withdrawal syndrome known as delirium tremens.

Also known as a rally pack, a banana bag often is given to those suffering from malnutrition associated with acute alcoholism. This is necessary because many alcoholics have poor diets, and alcohol inhibits the absorption of dietary nutrients. The IV solution usually is administered by a nurse according to a doctor’s orders, and it usually takes four to eight hours to be infused into the patient’s body.

In 2008, there were reports of banana bags being used by celebrities and fashionistas as a means of preventing malnutrition and dehydration during starvation diets for weight loss. This practice is not recommended by medical professionals, however. A banana bag does not contain all of the nutrients necessary to sustain healthy bodily function and should not be used as a replacement for an adequate diet.

There also are numerous nonmedical items that are referred to as banana bags. One is a bag that can be used for storing bananas in the refrigerator. Among the others are a type of ladies' handbag and a Muay Thai boxing apparatus that is used to practice punching and kicking.