The thymus gland is found behind the sternum in the middle of the chest. It plays a significant role in the immune system, especially in unborn and very young children. The theory behind the use of thymus extracts is that they might stimulate or normalize immunity. However, there is no reliable real evidence as yet that any thymus extracts are effective for any health condition. Furthermore, there are significant safety concerns with thymus products.


Thymus extract is produced primarily from the thymus gland of cows. This has led to concerns regarding "mad cow" disease. All the studies described below used a pharmaceutical-grade form of thymus called Thymomodulin. It is not known whether the thymus supplements available as a dietary supplement would have the same effect.

Therapeutic Dosages

The dosage of thymus extract used in studies has varied widely, depending on the particular thymus product used.

Therapeutic Uses

Two double-blind placebo-controlled trials enrolling children with frequent respiratory infections, such as colds, found that treatment with thymus extract reduced the rate of infection.1,18 In theory, this might indicate an immune-boosting effect. However, small studies cannot provide reliable proof that a treatment is effective. Weak evidence from a rather convoluted trial hints that thymus extract may also be helpful for preventing respiratory infections in adults.19

Intensive athletic training can suppress immune function and lead to colds, as well. However, a double-blind, placebo-controlled trial of 60 athletes failed to find any significant evidence of benefit with thymus extract.2

Preliminary evidence hints that thymus extracts may be helpful for food allergies,3asthma,4,20hay fever,21 and eczema. If thymus extract really does help these conditions, it may do so not by boosting the immune system, but rather by calming it down and causing it to behave more normally.

Small double-blind trials of thymus extract for hepatitis B and C found marginal benefits at most.5-8

Injectable forms of whole thymus extract or chemicals contained in it have been studied as a treatment for numerous other conditions, including cancer, cold sores, dermatomyositis, eczema, genital warts, hepatitis, HIV infection, leukopenia (low white cell count), multiple sclerosis, psoriasis, respiratory infections, rheumatoid arthritis, scleroderma, and shingles (herpes zoster).9-16

The results of these studies have been mixed. In any case, trials involving injected thymus cannot be considered applicable to oral thymus products.

Safety Issues

Thymus extracts have not been definitely associated with any side effects. However, there are real concerns that any glandular extract might contain the virus causing "mad cow disease."17 Keep in mind that there is relatively little governmental regulation of thymus products sold as dietary supplements in the US. Even when a ban is placed on importation of cow glands from a country where mad cow disease has been found, the ban does not apply to dietary supplements! For this reason, we recommend that you do not use thymus products sold as dietary supplements unless they are certified as free from risk of infection.