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FDA approval of Synthroid



More than seven years ago I read that synthroid had never been approved by the FDA. I emailed the company that makes synthroid and asked them about this. They replied saying that is was true that they had never been approved, but that they stood behind their product. Just recently I emailed the FDA about the approval of synthroid and they said that it was approved Sept. 2002. I`ve been on synthroid since 1982. For twenty years I was on an unapproved medication. Who do we trust?


It seems that we’ve answered a similar question about Synthroid in the past – probably around 8-10 years ago. Synthroid is a brand name for levothyroxine. Levothyroxine is the main hormone produced by the thyroid gland. Levothyroxine is indicated for replacement therapy for thyroid hormone in patients who cannot produce adequate amounts of this hormone on their own.

The issues are complicated and involve the history of scientific medicine and governmental regulation of the pharmaceutical industry. First of all, levothyroxine has been known to effectively treat the signs and symptoms of hypothyroidism for much longer than 30 years. In fact, the first use of a thyroid preparation for hypothyroidism is documented as far back as 1891. By the 1920s, this treatment was well established. Back then, patients with hypothyroidism were treated with processed desiccated pig thyroid glands.

Baxter Labs patented levothyroxine in 1959. Synthroid was first marketed shortly thereafter. In 1962 the Kefauver Harris Amendment to the U.S. Food and Drug Act required that pharmaceutical manufacturers provide scientific proof that their products were effective for the diseases they were meant to treat before they could be marketed. Prior to the amendment, drug manufacturers only had to provide evidence that their medicines were safe. Safety had been mandated by an earlier amendment in 1938.

The key phrase is “before they could be marketed”. Drugs that were already on the market, like Synthroid, were “grandfathered in”. Thus the drug manufacturer was not required to go through the rigorous drug approval process that was created by the amendment and currently exists. Strictly speaking, the drug was approved by administrative agreement, since it was already on the market and had the more or less proven track record that comes with successful treatment of hundreds of thousands probably millions of patients.

One thing that has been clear about levothyroxine over the years is that small changes in dose can make the difference between success and failure when treating hypothyroidism. One has only to look at the numerous incremental tablets strengths to begin to understand the situation. Other small, but important, differences can occur if a patient is stabilized on one product and then switched to another. There can also be batch to batch differences within the same brand.

The manufacturers of levothyroxine products made use of this fact to discourage switching between available levothyroxine products. For years, Synthroid was the de facto drug of choice for treating hypothyroidism largely because so many physicians had large numbers of patients stabilized and happy on the drug.

Around 1999-2000, the FDA determined that they had received enough consumer complaints about thyroid preparations over the years to warrant a thorough re-evaluation of these products. The method they chose to do this was to make levothyroxine a new drug. By doing this they forced interested drug manufacturers to provide evidence of safety and efficacy. The question of efficacy had been clearly established by long use, but the complaints related to adverse effects related to small differences in bioavailability and batch to batch consistency needed to be resolved. The FDA required the manufacturers of levothyroxine to provide proof that their product provided consistent delivery of the drug over time.

The manufacturers of Synthroid provided this information to the FDA in 2002 and the drug was approved as a new drug at that time.

You should feel comfortable that the medicine you have taken for nearly 30 years is safe and effective. Who should you trust? First, your own body: apparently you are doing well enough taking your Synthroid; second, your health care providers who have considered the issues and opted to prescribe Synthroid for you.

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