Carnitine for the treatment of Hyperthyroidism and obesity

This topic was originally presented at Hahnemann Medical College on November 1, 2002.


In 1965, I was training to become a clinical pharmacologist, a specialist in conducting clinical studies, at St. Vincent’s Hospital and Medical Center in New York City.  One day, my colleague and physician friend, Sheldon Gilgore who later became President of Pfizer Pharmaceuticals, 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 was experienced 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, conclude that certain clinical effects possibly couldn’t have happened 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. At that time carnitine was not available in the U.S. so we obtained our supplies from a French company.

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! I assumed that carnitine blocked the production of thyroid hormone by the thyroid gland.  Not so.  Thyroid function tests showed that the gland continued to produce excessive amounts of thyroid hormone.  I then postulated that carnitine must have-somehow, some way-blocked thyroid hormone activity peripherally.

We then decided to conduct a second study.  I gave two groups of healthy volunteers high doses of thyroid hormone. One group also received carnitine and the other a placebo. The results supported our belief that carnitine blocks thyroid hormone peripherally.2

As with the adriamycin-carnitine cancer 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 our findings  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 second clinical study, I 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 significant 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 adverse 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.It has been shown, however, that, in patients given exogenous thyroid hormone, carnitine has a beneficial effect on bone mineralization.This study also supports the weight loss hypothesis.

With the obesity epidemic in the United States coupled with the reality that exercise, diet and anti-obesity drugs have failed to stem this epidemic, it is past time that this possibility to treat this condition be clinically evaluated expeditiously.

Carnitine is available both as a drug by prescription and a dietary supplement found in the health food and other stores.

N.B. This article was published for general information. If interested, patients should consult with their physicians.


  1. DeFelice SL, Gilgore SG 1966 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


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