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Levothyroxine (Synthroid) Supplement Interactions


Levothyroxine (Synthroid, Levoxyl), liothyronine (Cytomel), and other thyroid hormone drugs for hypothyroidism (underactive thyroid), can be affected by taking supplements and can affect your ability to absorb certain vitamins and minerals. Care must be taken with regard to using these supplements, which include calcium, iron, and soy (including soy protein powders and soy isoflavones -- found in some menopause supplements) (which can affect absorption of thyroid hormone drugs), alpha-lipoic acid (which may lower levels of thyroid hormone T3 and increase levels of TSH) and L-carnitine and acetyl-l-carnitine (which can inhibit the activity of thyroid hormones -- and may help people with hyperthyroidism, or overactive thyroid).

Antacids containing aluminum hydroxide and magnesium hydroxide  (such as Maalox) should be taken at least four hours before or after taking levothyroxine, as they may delay or prevent the absorption of the drug (Synthroid Prescribing Information 2017).

There is some evidence that kelp supplements (such as tablets and capsules) can increase levels of TSH (thyroid-stimulating hormone).

Although often promoted for thyroid health, iodine supplements will not help your thyroid work better, and may even cause problems, unless you have an iodine deficiency.

Preliminary evidence suggests ashwagandha may increase thyroid hormone levels, and so should be used with caution in people taking thyroid hormones, or people with hyperthyroidism.

Be aware that high doses of biotin (as found in some B-complexes or supplements for hair and nails) may interfere with certain thyroid laboratory tests.

Resveratrol has been shown to increase TSH levels and cause thyroid enlargement in animals, although it's not known whether it effects thyroid function in people. 

Long term exposure to high or even moderate amounts of lithium can affect thyroid function.

Also, be aware that some thyroid-boosting supplements, including herbal supplements, have been found to contain thyroid hormones at significant levels, which are not listed and may be due to drug spiking. See the details in our Warnings section.

Certain foods and drinks may also interfere with absorption or bioavailability of levothyroxine. Soybean flour, cottonseed meal, walnuts, and dietary fiber may bind and decrease the absorption of levothyroxine from the gastrointestinal tract; grapefruit juice may delay the absorption and reduce its bioavailability (Synthroid Prescribing Information 2017). There is also some evidence that coffee may bind to and reduce the absorption of levothyroxine; the evidence suggests it may be best to wait one hour after taking this medication before drinking coffee (Benvenga, Thyroid 2008; American Thyroid Association). [Note: It is not known which compound/s in coffee are responsible for this effect. Therefore, it is possible (but not proven) that decaffeinated coffee may also reduce absorption (Wegrzyn, J Acad Nutr Diet 2016).] Green tea may also interfere with thyroid hormones, so it may be best to consume green tea, as well as green tea supplements, at least one hour apart from thyroid medication.

Cruciferous vegetables such as broccoli, brussels sprouts and cabbage contain compounds that can interfere with thyroid function. However, these compounds are typically found in only very small amounts in these vegetables, and they appear to be deactivated upon cooking (McMillan, Hum Toxicol 1986; Felker, Nutr Rev 2016). See our Answer about supplements and thyroid function for details.

About generic versions of levothyroxine:
The reason why it's particularly important to consider possible supplement interactions when taking thyroid medication is that it has a "narrow therapeutic index." This means that drug levels must be maintained within a relatively narrow range to be effective and not cause side effects. For this same reason, switching from a branded thyroid medication to a generic, or from one generic to another, can be problematic if the two drugs are not closely bioequivalent or are formulated differently -- causing one to release its active ingredient at a different rate than the other under certain circumstances, such as when taken with food or without food.

Due to historic concerns with generic versions of thyroid medication, the FDA tightened the bioequivalency requirements on generics in 2007. Nevertheless, many physicians have continued to prescribe the branded versions. In a study funded by the FDA to validate the equivalency of generic drugs, researchers reviewed the medical records of thousands of people newly started on generic (Mylan, Sandoz, or Lannett) or branded (primarily Synthroid or Levoxyl) levothyroxine for mild hypothyroidism between 2008 and 2017. They found similar attainment of normal thyroid status regardless of whether generic or brand-name medicine had been administered (Britto, JAMA Network Open 2020). While this is encouraging, it should be noted that the study did not evaluate the effects of switching from branded to generic (or generic to branded) products, nor did it include patients with moderate or severe hypothyroidism. In addition, there have been recalls of generic thyroid medication found to be subpotent or superpotent.

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February 15, 2021

I take (Triosint) it is a pure form levothyroxin. Triosint is made in Switzerland and has no additives. It is expensive my insurance company keeps threatening to put me on generic drug. I also use Armour which has been a life saver, as it gave me more energy. I take my medication when I usually get up to use the bathroom about 3 am. It is important to take it at least an hour before I eat. Calcium infers with the defectiveness of these drugs. I hope this helps someone.

October 26, 2020

What the study did not look at, and which is major new issue with generics, are the inactive ingredients, which not only can differ from one manufacturer of generics to another but also from generics to the brand. Some inactive ingredients could have problematic side effects. There was a first major study of these published within the past year, which caused the FDA to convene a panel to look into the issue. The. COVID hit. There was a second study on possible toxicity published a few month ago.

I know that I cannot take generic versions of many meds where I can take brands or authorized generics. I would suggest that people pay close attention to this emerging issue if they’re considering switching from a brand.

October 25, 2020

Thank you for this information, which I follow when taking supplements. Of course I always check before buying and taking any supplement.

A note about generic levothyroxine: 30 years ago I was started on Synthroid, then with an insurance change was moved to a generic levothyroxine. About a decade ago, I started having odd food reactions (hives after eating say, organic romaine lettuce, which had been harmless to me the prior day). Thanks to a clever allergist, it was determined that I was being overmedicated by the generic levothyroxine (my TSH was well below normal) - despite there being no change in my supplements, dosage, diet, weight, etc. It was causing me to react to food the oxidation of food that wasn't absolutely fresh, even a day after purchase of fresh foods, or opening a jar or bottle of prepared foods. I'm ever grateful to him.

Fast forward to a couple of years ago, and I had an actual thyroid episode, again the result in overmedication, despite my generic levothyroxine dose having been lowered, and lowered and lowered. Grasping at straws, I asked my doctor to put me on the more expensive Synthroid brand, and have had zero incidents since then. My heart doesn't feel as if it's going to beat out of chest, I don't have the shakes and the flop sweats, etc.

Some sleuthing by my husband resulted in the discovery that *every single manufacturer of the generics I had been on had had recalls, recalls and more recalls because of inaccurate levothyroxine dosing.* As the one taking the medication, was I ever notified? No. In fact, when presented with this information the online pharmacy shrugged it off, and continue to use these manufacturers despite their terrible practices.

Your mileage may vary, but no more generics for me.

August 26, 2021

I had a similar issue. I was on generic levo for years with no problem. Suddenly, I was a mess. Crying for no reason, hair falling out etc. I did not even suspect the generic drug (it was the only prescription I was taking) until Express Scripts started to send me the brand Synthroid instead of the generic, We all know how hard it is to get brand name meds covered by insurance, especially when my doctor nor I had ever asked, Sure enough, I found an article that levo being sent from Pakistan to the east coast had way too much medicine in it. Express scripts began sending me the generic again after 3 months, but I refused to take it again. I bought Synthroid myself without insurance, but it became very expensive. My doctor finally wrote a script for the brand Synthroid and that I was not to get the generic. She dated the order until 2099! She must have great faith in her ability to keep me alive till then. No problems since then.

October 25, 2020

Regarding CL's latest 10/2020 comment about switching from generic to branded and vice versa, it's worth noting that a big risk of taking the generic is that many insurance plans require patients to fill prescriptions via 90-day mail orders, and mail-order pharmacies routinely change the sources of their generic drugs. Reading into the CL comment, this means that your dose of thyroid medication could vary from one refill to another. This risk is another reason to seek out the branded versions.

February 26, 2020

This is an older CL post but I thought I'd share my experience regarding Nature Throid. Within the last decade, I switched from Levothyroixine to Nature Throid and although I seemed to feel better and had fewer hypo symptoms, those years when I was on Nature Throid, my TSH/T3 and T4 numbers were not stable. It seemed that each year or every other year, I had to have my Nature Throid dose adjusted.

What greatly interested me, however, was the fact that the Nature Throid is not part of the Medicare Part D formulary because it is not considered the standard treatment for hypothyroidism. When I research this issue, I find that the company producing it and similar desiccated thyroid products refuse to submit their products to testing to get properly approved by FDA. Why is that? I believe, based on my own experience, that the desiccated products are inconsistent in their levels of thyroid hormones, which is why the producers avoid getting them formally tested and approved.

After several years of using Nature Throid, I switched to Synthroid (NOT the generic of it) and I feel so much better. My eyebrows have grown in thicker too (which I've never had happen in years of using Nature Throid or Levothyroixine). It's my belief it's because the Synthroid is stable in its dosage and this has been more beneficial to me than getting scattershot amounts of T4 and other hormones in the Nature Throid.

This is my personal belief and experience but it would be insightful to have someone like CL look into the back story of the desiccated hormones and whether the true dosage varies from lot to lot.

January 8, 2020

My neurologist prescribed R-lipoid acid under the Doctor's Best label. Would it interfere with levithyroxine as well?
January 13, 2020

Hi Virginia - Unfortunately there does not appear to by an research on R-lipoic acid and levothyroxine.

January 31, 2019

I took Synthroid for over 20 years and felt terrible the whole time. I could not get a doctor to prescribe the natural thyroid. I finally found a doctor a year ago that prescribed Armour Thyroid and the change has been amazing.
I lost weight, my brain works again, I have energy and my hair is growing back. Please look around until you find a doctor that listens. It will save your life.

July 5, 2020

I, too, switched to Armour Thyroid 2 years ago. I couldn’t be happier. There has been one small increase during this time period. I feel great. Unfortunately my insurance will not pay for it, so it is “out of pocket” with the store’s discount. Still worth it as same insurance wouldn’t pay for trademark Synthroid, only generic. THAT was not acceptable to me. The AT has both T3 and T4. I previously also had to take generic Cytomel. Again not acceptable..

December 29, 2018

For many years the only thyroid medication I have taken is Nature-Throid. I take it first thing in the morning and as a sublingual for better controlled absorption. As I aged regular testing provided need for gradual small increases in dosage and at age 80 it is still doing a great job of keeping me active and feeling good. And yes, 35 years ago I had to push hard to get my MD at the time to even do the tests, let alone get him to prescribe some weird natural medication that my research had shown was the best way to go. My wife has also taken N-T for many years and it continues to work great for her also. Just get good thyroid testing with an informed interpretation. My doses work to keep TSH at about 0.9 for best results.

January 3, 2019

I found this post very informative since I used to take Nature-Throid as well, and found that my thyroid tests showed better results. I also had to really push to have the proper tests done and to get the Nature-Throid prescribed. Within the last year, my local small town pharmacy has informed me they can no longer get it. I thought that was because it was no longer available, but after seeing these posts, I will definitely begin calling other pharmacies to see if I can get it elsewhere. Thanks for posting on this subject!

September 23, 2017

When I was on prescription lithium some years ago, my thyroid medication dosage had to be increased. When that was discontinued, my thyroid medication needed to be decreased.

September 18, 2017

I have used Ashwaghanda & bladderwrack for a year & my blood tests reveal a normal thyroid

October 3, 2017

That's great to hear. My experience with those two supplements have also been really positive--more stamina and energy.

July 6, 2020

Hi Karen and Virginia, did either supplement affect your FT4 or FT3 levels in bloodwork (in either direction), and does that appear to be permanent or temporary? Thanks!

September 13, 2017

Some patients on synthetic thyroid medications who are not doing so well on them, might consider Nature-throid or Armour thyroid, which is made from dessicated pig thyroid, contains several hormones, not just T4. Some patients do much better on this medication, and it's much cheaper, too.
But most doctors have to be pushed to prescribe it, and some do not know the conversion dose when changing from synthetic to the natural hormone.

September 20, 2017

I was on 88 meg of levoyhyroxin for several years. Blood work every 6 months revealed a decrease in T-3 and reverse T-3. I have been on 60 (mcg?) of Armour Thyroid for 60 days and feel SO much better. Coincidently, I have lost 7 lbs and 2.5% body fat without ANY CHANGE in diet or exercise. Blood work is scheduled in November so I will be interested to see new results.

December 4, 2017

I’m newly diagnosed and on 100mg of synthetic thyroid meds. Would love hear more about your progress. Good Luck

January 7, 2018

From much research and according to my naturalpathic doctor, Armour or Naturthroid is the better and healthier choice for thyroid help. It is my understanding that many experience side effects or little help on Synthroid, etc. I take 120 mg. Armour first thing in the morning, but often follow with coffee soon after. So I appreciated hearing the comments on holding off on coffee until later.

September 9, 2018

i am one of those people for whom Armour worked much better than synthroid

March 22, 2019

T3 down and rT3 down? U sure.

June 16, 2019

Karen, can you give us an update?

September 13, 2017

Because of extreme fatigue (I am diabetic) my endocrinologist increased my dosage of Synthroid. It did not help the condition, but caused palpitations. Thyroid tests alerted me -- and research indicated the dosage was responsible. I asked the doctor to lower my Synthroid to a previous level, and the palpitations ceased.
Several posts here speak of PALPITATIONS. I suggest they evaluate their Synthroid dosage. Can't hurt!

April 16, 2017

I recently spent six weeks in a rehabilitation facility. The nurse came around at 5:00 a.m. to administer Synthroid on an empty stomach. She came back at 7:00 with my meds for high blood pressure. I decided a two-hour separation between the two types of drugs is a good idea; it allows the thyroid hormone time to be fully absorbed in an empty stomach and get into the bloodstream. Back at home, I wake up several times during the night to go to the bathroom. If it's near 5:00 a.m. or shortly thereafter, I take Synthroid. Occasionally, I oversleep and take it much later. But I always wait two hours before taking my other meds and eating breakfast. Sometimes, I have a cup of coffee between 5:00 and 7:00, but I seem to have palpitations if I drink coffee a long time before eating food or taking blood pressure meds.

June 11, 2019

Coffee or tea can interfere with thyroid med absorption. I was told to wait at least an hour after taking it before I have tea,
June 11, 2019

Thank you Jane, we've noted this in the Answer above. You can find more information about green tea and it's effect on thyroid hormones in the "Concerns and Cautions" section of the Green Tea Review

January 9, 2020

My friend used to take her synthroid and then have coffee
Her hair started falling out
Doctor told her It was from the coffee
Must wait at least one hour between taking synthroid and coffee or anything for that matter
Her hair came back after changing her routine

February 12, 2017

I take Synthroid and need to discuss, with my endocrinologist, the time to take it. I get up at night to go to the bathroom, and was taking my Synthroid then. But I then got palpitations about four hours later. So I changed the time to take it, to after I got up. That stopped the palpitations, but I do like my morning coffee, so it's hard to wait an hour before coffee. And I'm not sure that's even enough time.

February 12, 2017

I take Synthroid and I am considering switching to a night dose. To take on an empty stomach, how much time is actually needed to wait after the last meal? I have heard several different times: 2 hours, 4 hours, 5 hours. ConsumerLab what is the standard?
February 12, 2017

Food has typically cleared the stomach within 2 to 3 hours.

Virginia 15327
July 26, 2017

My understanding is that one should take Synthroid in the morning on an empty stomach, at least 1 hour before food is introduced. My endocrinologist explained that the natural hormone it replaces begins about 4 A.M. as part of the circadian rhythm. So, we should try to mimic as closely as we can the body's natural rhythms. Taking it at night would be inferior to taking it in the morning. I suggest talking this over with your endocrinologist before you make this change.

October 2, 2016

After decades of stability, for the past few years, my thyroid tests have been up and down. varying up and down by about 25 mcg. Of course it was affecting how I felt as well, which was the worst part. I was having palpitations at night, and went from feeling manic to exhausted.

As it happened, I came across the following article about coffee interfering with thyroid medicine:

After consulting with my doctor, I stopped taking the thyroid supplement in the morning with my coffee, and began taking it just before bedtime. Lo and behold, my thyroid needs went down, and I'm back to being at a stable dose of 150 mcg.

Good luck, and I hope this is helpful to others.
October 3, 2016

Thank you for making this point and sharing your experience with this, Rebecca. There is evidence that coffee can interfere with absorption of L-thyroxine (T4) (

January 25, 2017

Per my endocrinologist told me from the beginning that thyroid meds are to be taken first thing in the morning on an empty stomach, with water only. Then you must wait an hour before ingesting anything else such as other meds, supplements coffee and food. This hour is to give the thyroid meds time to fully absorb whereas these other things would interfere with proper absorption. After the hour you can take your other meds, supplements, coffee and food. An Endocrinologist will confirm this.

By the time I get to work an hour has passed and I can take my blood pressure meds and coffee, etc.

Kudos if you can take it at night but, if you do, you must make sure you have not had anything but water for several hours prior which is basically fasting. So, it seems like less of a hassle to wait until morning because you fast as you sleep. Peace and love.

January 25, 2017

I take my thyroid med immediatly upon wakening. I take about 1/2 hr getting showered, dressed etc & somwtimes longer if I go for a walk. I avoid calcium & mineral supplents until lunch time. I consistently have coffee or caffeinated tea with milk or cream with a small 'bite'. My MD says to do what I want, consistently, and he would adjust to the medication to get the right result. I've done this since starting levo in 2010. Now, my TSH remains stable ...usually between .5-1.0.However, my TSH levels were more solidly stable (more narrow range) once I switched to Tiroscint. I had stomach symptoms with dye free levothyroxine where with the Tiroscint I did not. I question if there is a relationship between fillers and absorption. As mentioned, I, too, become sleepless or sleep terribly if I take it before bed.

July 26, 2017

A few years ago I read a study (by endrocrinologists) that showed taking Synthroid before bed resulted in better absorption. So I suggested to my mom that she switch, then she wouldn't have to wait for her morning coffee. Shortly after, she commented that she overall felt better taking it at night, and her lab work stabilized. The study didn't include Armour Thyroid, which is what I take, but I also switched to a bed time dose, because I'm a teacher (I can't wait an hour to get to work to eat breakfast and have coffee).

September 10, 2017

I have found it simplified my routine to take my supplements in the morning with breakfast and thyroid medication right before bed (I refrain from late eating). It does not give me any sleeping problems.

July 6, 2020

i have heard many people state they feel better taking levothyroxine at night. i think each person has to figure out what is best for them.

January 13, 2016

I take Alpha Lipoic Acid for blood sugar and neuropathy and also Levothyroxin for Hashimotos Thyroiditis.
I make sure my vitamins and supps are taken by noon. Levo is taken on an empty stomach before I go to bed- an hour or more after eating.
There should be no interference and from my thyroid lab results, no problem at all. Be sure to take your Thyroid med on it's own and way after food etc is absorbed and processed,

January 15, 2016

Many people, including my mother, experience insomnia when thyroid hormones--such as Levothyroxine--are taken at night before bed. In my mother's case, she found it helpful to take Levothyroxine immediately upon waking. To avoid any interference with thyroid hormone absorption, she takes nutritional supplements at least 4 hours later with lunch and dinner.

February 23, 2016

Does Alpha Lipoic Acid help with peripheral neuropathy? I also am pre diabetic.
February 23, 2016

Hi Barbara - There is some evidence it may be helpful. See the "What It Does" section of the Alpha Lipoic Acid Supplements Review ( and this CL Answer ( for more information.

February 8, 2017

My heart doctor recommended alpha liopic acid for neurophy with my diabetics 2 and it helped me.

February 12, 2017

I added ALA to my regimen for neuropathy. Then my neurologist suggested CoQ-10; I am up to 200 mg twice daily. I cannot tolerate gabapentin or Lyrica. These two plus Deplin [methylfolate/active form of folic acid] do help but I am still opiate dependent. I also lack the MTHFR gene which has an essential enzyme for the conversion of B9 to a usable form. I take brand Synthroid. And prednisone. Because my sleep and eating patterns are all over the map, as was my TSH, we decided I would take my Synthroid with everything else I take in the AM because I usually eat at bedtime. That includes minerals, coffee, etc. But it works to keep TSH between .8 and 1.8. The less prednisone I am on the more Synthroid I need as it suppresses the antibodies at higher doses. Crazy dose now of 25 mcg 4x a week and 1/2 tab on Wednesday. Oy. It is a balancing act for sure.

July 6, 2020

have you considered taking in the middle of the night? i take about half of my daily T3 dose along with my full T4 dose in the middle of the night, and even as someone with very persistent sleep issues, it has relatively painlessly become a habit and i’m able to fall back asleep quickly after downing the meds. may help to stabilize you much better.

August 25, 2014

If you follow the citation link regarding aLA and thyroid (single study done in Germany, 1991), only the abstract is available on PubMed. It does not mention the number of patients involved but does describe that aLA was given with T4. It is not clear if these were hypothyroid patients or "normals". If these were normal people, then decreasing the conversion of extra exogenous T4 to T3 may be a good thing.
Unfortunately, as with a lot of the reported benefits of supplements, there is a lot of maybes and mights with potential side effects as well.
Hopefully the FDA will one day get more involved and demand higher quality studies.

February 12, 2017

FDA wish they could get involved. When Congress evaluated whether FDA should regulate "nutritional" supplements, they decided nutritional supplements are probably safe and do not need to be regulated. Hence all of the problems with what's on the market today.

August 6, 2014

The comments herein about alpha lipoic acid and acetyl L-carnitine indicate they are a hindrance, yet for a number of years they have been touted as wonderful supplements. I'm searching for the truth. Much of what I read about various supplements is contradictory from time to time.

January 25, 2017

I find that for everything said to be wonderful to eat or take, someone else seems to say it is bad or harmful for some other other condition. It's confusing at best. My method is to make myself an experiment of one and see how it works for me. Others may get a totally different result.

October 25, 2020

Yeah, listen to your body. You are the best judge of what works or not for you.

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