Carnitine for the Treatment of Hyperthyroidism -and- Carnitine and Thyroid Hormone, A Potential Treatment for Obesity

By Stephen L. DeFelice, M.D.


In 1965, I was training to become a clinical pharmacologist at St. Vincent’s Hospital and Medical Center in New York City. One day, my colleague and physician friend, Dr. Sheldon Gilgore, visited my research unit and told me about some European clinical studies which reported that carnitine is effective in the treatment of hyperthyroidism or an overactive thyroid gland. He came to me because I was also trained as an endocrinologist and had much experience in treating patients with thyroid disease.

I reviewed the data and found that the studies were poorly conducted and would not be accepted by quality medical journals. I did, however, notice that, though the studies were not well controlled, certain clinical effects occurred which probably didn’t happen by chance alone.

Since carnitine is an exceptionally safe natural substance, I decided that it was reasonable to test this substance in a few hyperthyroid patients.

Three female patients with classic hyperthyroidism were selected. All had the common manifestations of tremors, weight loss, nervousness, insomnia, heat intolerance, excessive sweating and emotional instability.

I treated them with carnitine, and within a ten-day period all three were virtually without signs and symptoms. (1) Then came the surprise.

The assumption was that carnitine was blocking the production of thyroid hormone by the thyroid gland. Not so. Thyroid function tests still showed hyperactivity continuing to produce excessive amounts of thyroid hormone. I then postulated that carnitine must have-somehow, some way-blocked thyroid hormone activity peripherally.

Dr. Gilgore and I then decided to take the next step. We gave two groups of normal volunteers high doses of thyroid hormone together either with carnitine or placebo. The results supported our belief that carnitine blocks thyroid hormone peripherally. (2)

As with the adriamycin-carnitine story, very little interest was shown in these studies. There were scattered reports in the scientific literature dealing with the carnitine-thyroid hormone connection, but not until the year 2002-thirty-seven years later-was a well-controlled clinical study published which confirmed that indeed carnitine does block thyroid hormone activity. (3)

There are a number of hyperthyroid patients in whom this property of carnitine could be particularly useful such as in pregnancy and patients that are difficult to control including thyroid storm.


In the aforementioned second clinical study that Dr. Gilgore and I conducted, we stumbled upon an unexpected finding. It is well known that excessive thyroid hormone, be it produced by the thyroid gland or given as a pill, causes weight loss. Much to our surprise, though carnitine blocked thyroid hormone activity on many clinical parameters, it failed to do so in the case of weight loss. The weight loss was equally as great in the thyroid hormone-treated group as it was in the thyroid hormone-carnitine-treated group.

This raises the intriguing possibility that the combination of carnitine and thyroid hormone may be a means to clinically treat certain types of obesity where the weight loss effect of excessive thyroid hormone is maintained while its side effects are negated.

There are some legitimate concerns that must be considered and evaluated. For example, thyroid hormone increases calcium excretion which may lead to osteoporosis. (4) It has been shown, however, that, in patients given exogenous thyroid hormone, carnitine has a beneficial effect on bone mineralization. (3) This study also supports the weight loss hypotheseis.

With the obesity epidemic in the United States coupled with the reality that exercise and diet have failed to stem this epidemic, it is past time that this promising treatment be clinically evaluated expeditiously.


Contrary to what you may hear or read, American medicine is, by far, the best in the world. But like many things in life, it can be greatly improved upon.

Educating physicians about non-FDA approved therapies is extremely risky. Our system is based on strong patents that are needed to justify the extremely high costs and risks involved in obtaining FDA approval for an NDA or New Drug Application, which legally permits pharmaceutical companies to spend many millions of dollars to educate physicians about the clinical benefits and risks of an approved product.

The costs to obtain an NDA are generally prohibitive for non- patented products, and it is very difficult to obtain strong patents for most natural substances which are our greatest potential weapons against disease. The large investment required to obtain FDA approval for the carnitine — thyroid combination will not happen simply because both are generic natural substances.

My personal experience with carnitine, magnesium and other natural substances is the reason that I proposed the Nutraceutical Research and Education Act or NREA. The latter is designed to encourage companies to sponsor clinical research on the specific dietary supplements and foods and legally make medical-health claims based on the results of the clinical studies at much reduced costs.

Congressman Frank Pallone (D-NJ) introduced the NREA in Congress in 1999. There was virtually no support from any dietary supplement or food company or their associated organizations. Evidently, they prefer to make marketing medical-health claims on their specific products that they sell that are not based on the results of clinical studies on their products.

1. DeFelice SL, Gilgore SG 1996 The antagonistic effect of carnitine in hyperthyroidism. Preliminary report. J New Drugs 6:351-353
2. Gilgore SG, DeFelice SL 1966 Evaluation of carnitine an antagonist of thyroid hormone. Clinical pharmacology report. J New Drugs 6:349-350
3. Benvenga S, et al. 2001 Usefulness of l-carnitine, a naturally occurring peripheral antagonist of thyroid hormone action, in iatrogenic hyperthyroidism: A randomized, double-blind, placebo-controlled clinical trial. Journal of Clinical Endocrinology & Metabolism 86(8):3579-3594
4. Rivlin, R.S. Medical Intelligence. Therapy of Obesity in Hormones.
NEJM 292:26-29, 1975.