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Can Acetyl L-Carnitine Be Taken With Levothyroxine?

author image Janet Renee, MS, RD
Janet Renee is a clinical dietitian with a special interest in weight management, sports dietetics, medical nutrition therapy and diet trends. She earned her Master of Science in nutrition from the University of Chicago and has contributed to health and wellness magazines, including Prevention, Self, Shape and Cooking Light.
Can Acetyl L-Carnitine Be Taken With Levothyroxine?
Underactive thyroid can cause thyroid enlargement. Photo Credit: JackF/iStock/Getty Images

Avoid acetyl L-carnitine if you are prescribed thyroid hormone replacement therapy with levothyroxine. There is some concern that acetyl L-carnitine may interfere with this medication. Clinical data suggests that acetyl L-carnitine naturally reduces your body's ability to absorb thyroid hormones. Consult your doctor before taking acetyl L-carnitine or any other supplements.

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Carnitine exists in several forms, including acetyl L-carnitine. However, it is collectively referred to as carnitine. It is a substance that helps your body convert fat to fuel. It transports fatty acids to your energy-producing cells for fuel use. Your body typically makes enough to meet your needs, but you get it from red meat and dairy sources as well. Research suggests that it may help prevent or alleviate overactive thyroid symptoms, though more research is needed, according to the University of Maryland Medical Center.


Your thyroid, an important endocrine gland, usually manufactures and secretes hormones that your body uses to regulate your metabolism. Your doctor will prescribe replacement hormone, such as levothyroxine, in the event that your thyroid is unable to produce enough hormone. This is called hypothyroidism, also known as an underactive thyroid. The most common cause is an autoimmune condition known as Hashimoto's thyroiditis, characterized by an abnormal immune response. Taking acetyl L-carnitine while prescribed levothyroxine may prevent your body from absorbing enough medication.


Carnitine acts as a thyroid hormone antagonist. This is confirmed in clinical research such as a study published in the November 2004 issue of the "Annals of the New York Academy of Sciences." The study found that carnitine prevents thyroxine and triiodothyronine from getting into your cells. These are your body's two primary thyroid hormones. Levothyroxine is a synthetic form of thyroxine, also known as T4.


Acetyl L-carnitine is a beneficial substance that plays an important role in energy metabolism. Forms of carnitine are used to help certain cardiovascular conditions and diabetic nerve damage. However, all forms of carnitine have the capacity to reduce the effectiveness of levothyroxine, which can complicate your condition. Avoid taking any form of carnitine if you are on levothyroxine. There is usually no need to restrict dietary intake, but consult your doctor if this is a concern.

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