There are several generic levothyroxine products available. A few years ago, the FDA required that all levothyroxine products obtain FDA approval. As a result, levothyroxine underwent certain tests to determine which levothyroxine products were equivalent to each other. Some levothyroxine brands and generics are equivalent to each other, while others are not. Your pharmacist is a good resource if you have questions on which ones are equivalent.
Levothyroxine sodium is a medication approved for the treatment of hypothyroidism (an underactive thyroid) and a few other thyroid problems (such as thyroid cancer, nodules, or goiters). Levothyroxine is only available with a prescription.
There are many different levothyroxine products, and, in the past, it was impossible to know if any of these products were equivalent to each other. As a result, it was not known whether any of the generic levothyroxine products were as good as the brand-name products (and whether brand-name levothyroxine products were equivalent to each other).
Past Problems With Generic Levothyroxine
Some people are unaware that the U.S. Food and Drug Administration (FDA) has never approved many prescription medications (usually older medications). These medications were already around before many of the laws and regulations were established.
Levothyroxine products were all unapproved drugs until recently. Because the FDA did not approve them, 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. Importantly, Levoxyl® and Synthroid® are considered to be equivalent to each other (as well as to several other products), although this was a controversial issue in the past.
Keep in mind that 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 he or she does not need to adjust your dose.