In the past, no versions of generic Synthroid were considered equivalent to the brand-name medication. However, several generic versions have since been shown to be equivalent to it. The generic versions are sold under a variety of different names and are available in several different strengths, ranging from 25 mcg to 300 mcg.
Synthroid® (levothyroxine sodium) is a prescription medication used to treat an underactive thyroid (hypothyroidism), as well as a few other thyroid problems (such as goiters, nodules, or thyroid cancer).
Synthroid is manufactured by Abbott Laboratories. In the past, there were no generic versions of levothyroxine that were considered equivalent to Synthroid, even though Synthroid is an old medication. However, several generic versions have since been shown to be equivalent to Synthroid.
Many people are unaware that many prescription medications (usually old medications) have never been approved by the U.S. Food and Drug Administration (FDA). Typically, these medications were already around before many of the laws and regulations were established. Synthroid, as well as all other levothyroxine medications, were all unapproved drugs until recently. Because they were not approved by the FDA, there was no way to know if any of these products were equivalent.
A few years ago, the FDA required all levothyroxine products to obtain FDA approval. This involved certain studies that determined whether any of these medications were equivalent (or not equivalent) to each other. The FDA has determined that many of the available levothyroxine products are equivalent to Synthroid, meaning that they should be just the same as Synthroid. You may find old information on the Internet or from healthcare providers who are behind on this information stating that Synthroid is not equivalent to other levothyroxine products, but this is not true anymore.
However, levothyroxine is a "narrow therapeutic index" medication, which means that tiny changes in the dose can result in large changes in the body. As a result, most healthcare providers recommend that you stick with one brand of levothyroxine if possible. If you do need to change brands, it is a good idea for your healthcare provider to do blood tests often to make sure that your dose does not need to be adjusted.