Glandular extracts come from the hormone-producing glands of animals, usually cows, but sometimes sheep and pigs. They contain dried and ground-up raw animal glandular tissues or extracts of those tissues - from the thyroid, thymus, adrenals, pituitary, ovaries, testis, and pancreas. A prescription form of animal thyroid extract is used by a few doctors to treat hypothyroidism, but most now use synthetic hormones. However, health food stores stock many products containing glandular extracts. Manufacturers claim that they can enhance immune function, correct hormonal imbalances, treat allergies, and combat inflammation. Some are said to have rejuvenating effects. I know of no credible evidence demonstrating that these products live up to their advertised effects.
Please be wary of the notion that a hormonal imbalance is the cause of whatever problem you're hoping to affect by taking a glandular extract. Diagnoses such as "adrenal insufficiency" and "thymus depletion" made by practitioners without medical training (including nutritionists, chiropractors, massage therapists and health store clerks) are unlikely to be valid. If you actually have one of these conditions, you should be under the care of an endocrinologist and not treating yourself with glandular extracts. Taking these products in the absence of a clear diagnosis can actually upset the body's delicate hormonal balance and make matters worse. Besides, these products may contain toxic contaminants and could, theoretically, transmit diseases like mad cow disease.
Bottom line: at best, glandular extracts are a waste of money. At worst, they could be dangerous. I strongly recommend against using these products.
Andrew Weil, M.D.