levothyroxine and Synthroid

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.”

Learn More:

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.

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  1. Marilyn

    After going on a small dose (25mcg) of levothyroxine my blood pressure has constantly increased to too high. My PC has put me on medicine for that as well. I’m on my second medication, and it’s not keeping the bp consistent. Any suggestions or ideas if with thyroid medication this is ever a problem?

  2. KIMI A
    san diego

    Hello, the problem is that we need stricter guidelines to be able to keep getting the same synthroid from same manufacturer to have our levels controlled and balanced, not switching them every 6 weeks! We need our synthroid to be EXACT MEASUREMENTS OF 100 PERCENT POTENCY EVERY TIME WE TAKE ONE, not under 100 percent one day and the next 80 potency the next and GOD FORBID 70%!There is no responsibility in pharma or fda in making sure our drugs have 100 % potency and same pill taken each day! The reason there is so much concern is the drugs are NOT MADE EFFECTIVELY AND DRS KEEP PATIENTS IN BLUE BOOK RANGES THAT ARE NOT CORRECT! A thyroid patient should be treated at 1 tsh level and be able to stay in that level while being treated on thyroid medication for optimal health. WE NEED FDA STRICTNESS IN MAKING PHARMA MAKE SYNTHROID THE EXACT SAME WAY EVERY TIME AND EACH PILL BEING 100 POTENCY OR THERE IS NO TREATING ANY THING AND Y OUR ALL WASTING YOUR TIME AND OURS! WE NEED MODERN SYTHROID AND TO BE ABLE TO TAKE THE SAME ONE THAT WORKS FOR THE PATIENT, NO ONE ELSE! DRUG COMPANIES NEED TO BE RESPONSIBLE IN MAKING THEM POTENT ENOUGH TO WORK! AND STOP CHANGING THEM!

  3. Jackie
    North carolina

    Well, I thought all this heart rapidity and sweating was old age. I had no idea Levothyroxine dosage could be the cause. I have had to change Drs., and she has not addressed a change. I have cut down to a former dosage and am waiting to see a change. I appreciate your knowledge so much, and the answers have helped as I had no idea anything could be attributed to thyroid meds. Thanks, friends.

  4. cindy
    Pacific Northwest

    I have taken thyroid medicine for years. At first, I had “thyroid storms” with sweating and heart palpitations. My doctor was forever changing the dosage to keep my THS level. When I started seeing an endocrinologist, she put me on Synthroid. She said the dosage was too important to trust to a generic. I never had another problem and my dosage has stayed the same for years.

  5. Colette S

    You cannot go off any drug one day —-& then start a new one next day. It has to be a very slowly . like take your new pill once a week then your regular the other six days then the following week take new meds twice a week ——this way it is a gradual . I learned this from Peoples Pharmacy about 20 years ago. I’ve always followed this rule & never had a problem switching drugs

  6. Lucy

    I took Levothyroxine for years. My BCBS changed my pharmacy from CVS to Walgreens. At first I felt better with more energy but then started feeling edgy. I had TSH done at doctor and they said I needed a higher dose. Unfortunately the numbers on the lab results got transposed. After having a panic attack I realized the problem. I asked to switch back to the lower dose I’d taken for years and to Synthroid. I feel better now. I’m 64 years old and now know that the elderly need to be more closely monitored for thyroid conditions. I bought you pamphlets on thyroid and gerd. Thanks for all your invaluable information.

  7. Nan

    I was diagnosed with. hypothyroidism nine years ago. I did a relentless pursuit of what, when, how, etc. with regard to my “diagnosis”. I found a study on the NIH website where L-Tyrosine and Selenium were used with great success as supplements along with prescribed Levotyroxine/Synthroid. Being a person who believes in vitamin and mineral supplementation I thought “why not?” and began a daily regimen with my Levothyroxine which for nine years has remained at the minimal dosage. Don’t know if this would work for everyone but sure has for me.

  8. dzrlib

    I took Synthroid after Armour Thyroid (from pigs) was no longer available. I never felt right and was very pleased when Armour Thyroid again was again made available. I switched immediately and feel much better.

  9. Karen M.

    About 25 years ago, a pharmacist told me that Levoxyl was superior to Synthroid. I followed his advice and took it successfully for years. Then it became difficult for my pharmacy to stock and generic levothyroxine was substituted. Only in retrospect could I see it wasn’t the same, and I went back to Levoxyl.

  10. June

    I have hypothyroid disease and took synthesis for years, then my insurance company forced me to switch to levothyroxine which, now, I think works better. But there is a big difference and a transition that disrupted my system.

    I had a big price increase in my levothyroxine it went from $4 to $14 for 30 days?????

  11. Sami
    South Carolina

    Sadly, I cannot afford the Synthroid brand. I took it for years when my insurance covered it. The past 5 years my insurance does not cover it so I switched to levothyroxine. I have found that IF you stay with the SAME manufacturer of the levothyroxine you are okay. It is when you switch mfr.’s that dosage is different. This has worked for me and is my opinion.

  12. Paulette
    New Mexico

    I have needed thyroid replacement for many years and responded well to Synthroid until three years ago. I was having episodes of vertigo that seemed to correspond to my taking the hormone. I was then prescribed Tirosint. The vertigo improved, but only for a few months. I was then prescribed the generic equivalent which not only gave me vertigo, but migraines. I then understood that I was allergic to the binders, fillers, and dyes in the pills. I all but stopped taking my medication, which made my doctors very unhappy, but I saw no alternative. I was unable to function taking any pre-made pill. I thought there was a good possibility I was going to die. It was that extreme. I then found an endocrinologist who came up with a very simple solution: Levothyroxine and sodium bicarbonate compounded in a capsule. I take 100 mcgs. a day and have had no vertigo or migraines for three years. The cost is $22.00 a month. I literally got my live back.

  13. Barbara

    I can’t take Synthroid brand. It makes me nauseated, shaky and I feel like I’m about to pass out. I noticed this after switching back from generic. My headaches returned and I literally had no energy. I felt the difference after three days. I immediately switched back to generic.

  14. Barbara

    After taking Synthroid for several years, my insurance switched me to generic levothyroxine. I developed red skin blotches over a 4 year period. I did not make the connection until a biopsy determined it was a drug eruption. The only drug I was taking was levothyroxine. My Dr switched me to Armour Thyroid, and the blotches are now fading.

  15. Joan
    Getzville, N.Y. 14068

    An expert physician who was taking Levothyroxine himself advised me to change from Synthroid to it myself & I now have been able to lower the dose under an excellent geriatric physician’s advice to 88mcgm daily – the only medication I take except for vitamins!

  16. Bonnie

    When I was first diagnosed with hypothyroidism I was prescribed Levoxthyroxine, and it didn’t do a lot to help with my symptoms. So I discussed being switched to the brand name with my Dr., and she readily agreed. I felt so much better and have been on 100 mg for several years now. I support using the brand name even though it is a bit more expensive.

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