The People's Perspective on Medicine

Levothyroxine and Synthroid Are Not Interchangeable

Many people have no difficulty switching between levothyroxine and Synthroid, but others develop distressing symptoms suggesting a difference in dose.

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

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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About the Author
Terry Graedon, PhD, is a medical anthropologist and co-host of The People’s Pharmacy radio show, co-author of The People’s Pharmacy syndicated newspaper columns and numerous books, and co-founder of The People’s Pharmacy website. Terry taught in the Duke University School of Nursing and was an adjunct assistant professor in the Department of Anthropology. She is a Fellow of the Society of Applied Anthropology. Terry is one of the country's leading authorities on the science behind folk remedies. .
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I was taking .5 mg of the generic Levothyroxine. A coworker said that the brand name Synthroid was better so I had my pcp make the switch at the same .5 mg dose. I don’t know if it is related, but in the month that I have taken the Synthriod I feel extremely fatigued & have gained 7 lbs. Any advice or suggestions would be greatly appreciated.

I had been taking levothyroxine for over 19 years. I came across an article that had very interesting information on the difference of the generic brand and the name brand synthroid. It mentioned that if you are taking the generic brand levothyroxine and still experiencing cold intolerance, weigh gain and fatigue, you may want to switch to the brand name synthroid, it does a better job of supporting the T3 then the generic does, and it also absorbs better in the system.

I just started taking the brand name today, so hoping it will help me with the cold intolerance. I was wearing a thermal shirt with another shirt on top of it, and also running my heater that sits under my desk, and was still freezing.

When my daughter was diagnosed with Hashimotos at age 11, the doctor at the children’s hospital gave us the advice to stick with brand name Synthroid because we would know the dose would be consistent. He said generic levothyrixine was good but that the pharmacy can switch their generic brand and even a slight change in formula can cause problems. So, if we always got the same generic brand we would be OK, but the pharmacy might get a different generic brand. He went on to say that in most drugs the slight variance would not matter, but in this drug it can matter a lot. She’s been on it for ten years now with no problems.

I’ve taken Synthroid for almost 40 years. I was also told by my doctor to stick with this one because the generic does not have the same strict guidelines (no idea if that’s true). For example, he said one day I may be taking 200, the next 180, and the next 190,etc. I also had a goiter so I was on an elevated dose to keep the goiter down.

However, about 5 years ago my daughter went on the generic and started developing rashes/welts all over. Her doctor prescribed claritin, which helped.

Then my pharmacy gave me the generic brand by mistake, and I started to develop welts within 3 days of taking it. The welts started at my neck and went to my knees. I knew the only thing I changed was this medication. I stopped and went back to Synthroid, and the welts went away in a couple days.

Apparently, we are allergic to whatever binding agent they use in the generic brand (think it is also used in certain types of Midol). Daughter only had the welts/rashes with generic and types of Midol.

I’ve had hypothyroidism for 30-years and never a problem until now. I have been switched from Levothyroxine to Synthroid more than once and thought they were interchangeable; never seemed to matter. I changed insurance’s and apparently, these doctor’s offices and decisions are not made by them but by insurance companies. In other words money.

I quit any processed sugars about 3 months ago and although I felt better for a while I started having severe headaches which only stopped when I drank (my usual quart of O.J. I believe, now, I have cut down to one glass instead of a half-gallon, literally, in the morning. The headaches have, mostly, gone away and I’ve heard of Tirosint as being the ‘cleanest” thyroid med on the market but very expensive.

I’ve, for the first time, have been experiencing heart palipatations, loss of weight, normal probably, because of my sugarless diet, I understand that but my lack of energy of any kind is the problem. I’m an ex-professional boxer who has trained since I was 15 years old and now can barely finish a walk with my wife. It is totally insane and I know there is something wrong. I have an enlarged prostate but cancer was ruled out and I take no pills for that (yet).

I just wonder if my thyroid level should go up or down and if I need an endocrinlogist as my primary admits he knows little about the thyroid and just goes by the tsh levels.

I went through menopause about 25 years ago. My pcp checked my thyroid levels and then recommended generic Synthroid. My thyroid levels were fine, and my tsh was about 9. He said I wouldn’t notice any difference in my health (I was healthy and not very overweight), but thought I should start the med in order to prevent hypothyroidism.

So, I was started on a low dose, then in three months a higher dose until I was taking 100 mcg. I didn’t notice feeling any better or worse, however, at the 3 months time, my hair fell out drastically. I had a good head of hair until then. When I asked my pcp about hair loss, he answered it wasn’t because of my med, but rather from some tragic or strong event.

I said there hasn’t been one. He wouldn’t change my prescription and said levothyroxine was the same as Synthroid. After the initial fallout out period, my hair loss lessened, but it continued. Several years ago, because the laws changed on the tsh level, my doctor increased my med to 125 mcg. My hair fell out a little more and again leveled off.

I have the male baldness pattern. Recently, I noticed my hair falling out again, and my scalp can be seen easily. My tsh was checked a couple of times several months ago and there is a little elevation in the number, around 3, but no increase in the med yet. My pcp does not think it necessary to test t3, t4, or rt3, and he goes only by the tsh. Is it possible I can go off levothyroxine slowly after all these years since I was diagnosed subclinical hypothyroid and never had low levels of t4? Or will going off now compromise my health and add to my hair loss?

I wish I had either waited at that time during menopause to see if my thyroid levels would change and/or stay normal. I now have heart palpitations once in a while (dr says normal) and I found out I have minor cardiac artery plaque. I’ve read thyroid problems often increase with age, so I’m not sure what to do. No matter what, I think I’ll go to an endocrinologist next visit for thyroid testing, but I’d like to know if anyone here has been diagnosed subclinical hypothyroid and successfully went of their thyroid med.

I fear after all these years my body has adjusted to the levothyroxine, but I’m afraid of continuing or going off and incurring poor heart health which path I take.

I’m afraid to switch to the generic because my Endo, who managed me through my thyroidectomy, told me to stick with Synthroid because the generics were unreliable. That was many years ago, but I’ve been stable on the same dosage for 30 yrs. Now my insurance is causing me to pay higher and higher deductibles in order to push me to go to the generic. I’ve heard all the stories. But this is killing me. I’m worried that if I switch, and I have problems, my doctor won’t believe me if I want to go back to it. All I can think of is to set up a plan for testing my thyroid before and after the switch. Any other ideas?

Please see an endocrinologist. I had my thyroid removed in 1999 due to thyroid cancer. For about 5 years I was treated my a GP. Big mistake. My numbers were all over the place and was on upwards of 175 mcg of Synthroid. I was almost 40 and felt like I was falling apart. My memory was so bad and I couldn’t string a good sentence together. It was frightening. I thought I was having some sort of dementia. I could actually SEE in my mind what I wanted to say. I could even see the words, but somehow I had to describe them because the actual words just would not come out. The straw that broke the camels back was when I said to my husband: “Could you please go to the place that has the big red letter between J and L because I need a new flippy thingy for the place where I cook food” In other words, Go to K Mart and get me a new spatula for the kitchen. This was my life. Going to a specialist was the best thing I did. I’ve been his patient for 15 years and I truly think he saved my life. GP’s are great for if you have a cold or something easy to treat, but once you have a condition that needs proper attention like a heart, blood sugar or hormone situation it really pays to see the specialist. Good luck. <3

I have had a thyroid issue for 18 years. I have been on and off levoxyl and synthroid, and now I am on 50 of levoxyl. My endo thinks I should try a 75mcg for 2 days–like take a 50 levoxyl and on weeekends take 75. Does that make sense to anyone? Please help me.

No it Doesn’t make any sense because this thyroid hormone stays in your system for 2 weeks or longer I believe.

Also my cardiologist told me that having 2 difference dosages in different days can affect your heart

Give it a try for a few weeks and see if it helps.

I switched insurance companies and the new company has had me take several generic drugs for trial before allowing payment for brand names. I can understand that and have no problem trying to follow their policies. I am on quite a few meds. I take care of my elderly parents who have had many health problems, especially the past few years. Mom is 80 and Dad is 85. During this past month I have definitely not been myself. The last straw was when I had taken my Mom to her doctor and made a couple other stops for her usual store needs.

It was nothing unusual, but she said I was not acting normal and I actually yelled at her. I had no control over myself or my emotions which seemed to be getting worse recently. I immediately drove to my doctor, went in and explained to the receptionist and got an appt for today. I have had many symptoms that are familiar to me from when I was on generic thyroid med (Levothroxin). This doctor knows me very well. I have been their patient for almost 20 years. The doctor told me I was the only person/patient that they had that had any problem taking generic Synthroid. I adore this person and have always believed that I could trust and believe in there knowledge and caring for me. Then the words, “I think it might be in your head.” came out. I was absolutely stunned. I’m hurt, embarrassed and a little bit angry.

I realize I could have summed this up in a couple sentences, but I so desperately needed to tell someone who would not judge me or be able to hurt me anymore than I was today. Then as I was preparing to leave, they told me none of it matters because in July 2018 all of the Medicaid companies will be using a universal set of policies. I am hoping for other people’s opinions and also if anyone else has heard of this possible change coming this year. Please accept my apologies for the length of this and my true appreciation to anyone who took the time to read this. Thank you.

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?

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!

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.

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.

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

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.

I had a thyroid removal two years ago and am on levothyroxine .088mcg. Despite being on Weight Watchers and following the program, am unable to lose weight and in fact have been gaining. Experiencing might sweats but dr. says blood levels are within normal range. Any suggestions on what to do for those who may have experienced similar problems.

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.

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.

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.

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?????

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.

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.

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.

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.

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!

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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