Researchers at the University of Messina report that supplementation with L-carnitine, a quaternary amine which occurs naturally in the body, can eliminate the side effects of thyroxine treatment and reduce the need for constant monitoring. It is estimated that goiter (enlarged thyroid gland) affects about 200 million people worldwide. It is far more common among women and is almost always the result of an iodine deficiency. It can often be corrected by increasing iodine intake. In some cases it is necessary to dampen the activity of the thyroid-stimulating hormone (TSH) in order to treat the goiter. This is usually done by prescribing thyroid hormone (levothyroxine). Levothyroxine, however, has many adverse effects and also needs constant monitoring to ensure that blood levels are adequate. The Italian randomized, double-blind, placebo-controlled, crossover trial involved 50 healthy women who had normal thyroid levels (euthyroid) at baseline. The women were allocated to a placebo group, to group A that received 2 or 4 grams of carnitine daily for two months out of the six-month trial period or to group B which received 2 or 4 grams carnitine daily for four months. All participants received 2-4 microgram per kg body weight per day of oral l-thyroxine throughout the trial.

The researchers measured a number of blood parameters and symptoms in the placebo and treatment groups. They conclude that L-carnitine supplementation significantly reduces thyroxine therapy induced weakness, breathlessness, palpitations, nervousness, insomnia, tremors, and elevated heart rate. Carnitine also increases bone mass (bone mineral density) by about two per cent after just four months of supplementation. In contrast, placebo group members lost bone mass during the trial. The researchers point out that L-carnitine is non-toxic and does not interact with any drugs. They suggest that L-carnitine supplementation (perhaps as little as 1 gram/day) can be of clinical use in goiter therapy and in the treatment of other thyrotoxicosis-related disorders such as amiodarone-related thyrotoxicosis.
Benvenga, Salvatore, et al. 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, Vol. 86, August 2001, pp. 3579-94