An ineffective thyroid gland that fails to produce enough hormone needs help. That is usually provided by a prescription for a thyroid hormone called levothyroxine. It is sold under brand names Synthroid and Tirosint.
We sometimes hear from people who had difficulties when they were switched from one formulation of the T-4 thyroid hormone levothyroxine to another. Most often, these were patients who were started on the brand-name drug Synthroid and found that their symptoms did not respond in the same way to a generic levothyroxine pill. Recently, we heard from a person whose switch went in the other direction. This person discovered that levothyroxine and Synthroid are not interchangeable.
Switching Between Levothyroxine and Synthroid:
Q. I have hypothyroidism and have been taking generic levothyroxine for a few years. My doctor and I have struggled to find the correct dosage and recently settled on 125 mcg daily.
I asked my doctor to prescribe branded Synthroid because I read it is better. He did so, at the same dosage level as the generic.
Within one day of taking Synthroid, I feel as if I am about to explode. I am anxious and my heart is racing. I also have diarrhea. Is there an explanation?
Adjusting the Dose When Changing Between Levothyroxine and Synthroid:
A. We have heard from many people that switching from branded to generic levothyroxine or vice versa can result in symptoms. Excess thyroid hormone can cause rapid heart rate, sweating, anxiety, tremors, diarrhea and irritability. Such a switch may require a dose adjustment. Please get in touch with your doctor and request titration.
Controversy Over Differences Between Levothyroxine and Synthroid:
This topic has been controversial for decades. Twenty years ago, a study determined that four different levothyroxine formulations, including Synthroid, were bioequivalent (Dong et al, JAMA, April 16, 1997). Although cost savings are the usual motivation for a switch to generic levothyroxine to Synthroid, a study of a large database of health records found higher rather than lower health care costs overall following such a change (Katz et al, American Health & Drug Benefits, March 2010).
The authors concluded:
“In the absence of cost-savings, there is no clear rationale for switching patients from brand to generic levothyroxine.”
To learn more about different forms of thyroid medicines, lab test interpretation and symptoms of too little or too much thyroid, you may wish to read our Guide to Thyroid Hormones. This 25-page guide may be purchased for $3.99 at www.PeoplesPharmacy.com.
You may also be interested in our most recent radio interview on thyroid health. In Show 1096, we discussed What You Need to Know About Treating Thyroid Disease with endocrinologist Antonio Bianco, MD, PhD, and patient advocate Mary Shomon.