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Thyroid Hormone Replacement and TSH Level

1. My TSH is quite suppressed. Is it possible that too much L-T4 (Synthroid) may be causing the extreme fatigue I am experiencing?

   Tamilia (Sept 1/11)
   
   Indeed, it is possible that suppressive doses of levothyroxine and subclinical hyperthyroidism (low TSH and normal free t4 and free t3) may be associated with symptoms and long term complications, namely arrhythmia (e.g. atrial fibrillation) and accelerated bone loss in post menopausal women.
   
   For these reasons the latest ATA guidelines recommend reassessment of the need for levothyroxine suppression periodically.  Basically, patient's risk profile and clinical status dictate the level of suppresion
   
   low risk profile ( stage 1 and stage 2, patient >45 yo), in remission------TSH = 0.3 to 2.0 mU/L
   high risk patient (stage 3 and stage 4, patient > 45 yo), in remission----TSH = 0.1 to 0.5 mU/L
   low and high risk patients with persistent disease       -----------------------TSH <0.01 mU/L
   
   As such it would appear that a low risk patient in remission can be treated with less levothyroxine and maintain a tsh level in the low/normal range

2. When one has been prepared for Tg testing or RAI treatment using Thyrogen, the level of TSH during the preparation week is less relevant. Why is that so?

   Driedger (Feb 1/11)

   When Thyrogen is used for testing or treatment it is known that the TSH always rises and typically to levels of 100-150; that is the reason for giving the injections. Therefore, there is not a reason to actually measure the value.

3. What does a decrease in my free-T4 (via blood test) mean? Is there an optimal range of T4 to maintain when being suppressed?

   Ezzat (June 1/10)

   The objective of management of patients with thyroid cancer is to keep TSH down (closer to 0.5) to avoid a stimulating effect on cancer recurrence. However, a markedly reduced TSH, as mentioned in your question, is more likely to result in a potential heart and bone disease without concomitant added cancer risk prevention. The T4 measurement is much like cholesterol. It is critical to know the fraction of where the hormone is being measured much like you want to know if your cholesterol elevation is in the LDL or the HDL fraction. Age, estrogen use, liver disease and other factors influence the T4 measurement. It can force upwards or downwards. As such, it is potentially misleading without accounting for other variables that can influence its concentration.

   Cheng (June 1/10)

   There is no optimal free T4 level at which suppression is obtained. The only suggestion is that the free T4 level remain in the normal range if possible. I would not be concerned about the falling level given that your dose of medicine has not changed. Just carry on as usual.
   
    

4. Why do I feel "brain fog"?

   We know that hypothyroidism can cause what some patients call "brain fog" (including forgetfulness, lack of focus, a feeling of being run-down, etc). However, some thyroid cancer patients find that even when their TSH level is at the level targeted by their doctor, they continue to feel this symptom. Why is that?

    

   Rodin (March 1/09)

   Both the patient's symptoms and the blood tests, including TSH levels, may reflect thyroid status. I believe that patients may be hypothyroid, even if it is not definitive from their TSH levels. It is important that patients let their endocrinologist or treating physician know about their symptoms in order to arrive at an overall judgement.
   
   Cheng (March 1/09)

   Recent clinical practice guidelines have recommended that complete suppression of TSH in the long term is not necessary in many patients with lower stage thyroid cancer after appropriate treatment. By allowing the TSH to rise into the near-normal range, the risk of bone loss and heart rhythm abnormalities are reduced. In addition, some patients feel better when TSH is allowed to rise to the near-normal range. Conversely, there are some patients that experience "brain fog". As one can imagine, this is difficult to study because of its subjective nature.
   
   Also, see the section about "menopause and 'brain fog' "

5. Does it help to take Cytomel (T3) in addition to Levothyroxine (T4) in order to “feel better”?

   Ezzat (Oct 1/05)

   Multiple studies have now confirmed that the addition of T3 to T4 does not offer any more benefit than T4 alone. These have been very-well conducted, controlled studies so the information appears reasonably solid. In most instances, not feeling well despite perfectly normal thyroid hormone levels indicate that there is likely another cause, other than thyroid, contributing to the symptoms.

6. Can TSH and other blood indices fluctuate during the day?

   Ezzat (Feb 1/06)

   It's important to remember that some, but not all, thyroid hormone indices can fluctuate.

   Free T4 is quite stable. Free T3 varies more on a number of factors the most common of which is the degree to which the person has fasted...the longer you fast before the sample the lower the value. Finally, the TSH values display a small, but measurable degree, of fluctuation throughout the day.

   HOWEVER, all these changes are NOT related to the use of thyroxine which has a long-half life of a week. Hence the changes in Free T4, Free T3, and TSH are not ACUTELY influenced by the timing of the last dose of thyroxine (T4).

7. What level of TSH is desirable for thyroid cancer patients?

   Driedger (June 1/05, revised Sept 26/08)

   The goal for the TSH level following ablation is about 0.1mU/L, at least until it is clear that the patient will not need additional surgery or I131. Thereafter, it may be acceptable to let the TSH rise to the low normal range. One should always measure the free T3 at the same time as the TSH to ensure that the patient is not over replaced. The T4 is not the most helpful test in this assessment because patients vary in the ability to convert the T4 to T3. In many patients, the T4 will be above the normal range when the TSH is adequately suppressed

   Ezzat (June 1/05)

   There is no general consensus on how low the TSH should be suppressed in patients with papillary forms of thyroid cancer. Classical practice indicated that TSH levels should be suppressed (generally under 0.1) irrespective of T4 levels in patients who are at high-risk of thyroid cancer recurrence. Only a small subset of patients who have had aggressive forms of papillary thyroid cancer would fall into that category. Moreover, thyroid hormone excess can cause deleterious effects on heart rhythm & function in those over 50. It is, therefore, advisable to balance the risks versus benefits of the need for and the extent to which the TSH should be suppressed. This decision needs to be made on an individualized basis in consultation with the thyroid cancer-treating physician.

   Ezzat (Mar 1/06)

   The concern is that too much thyroid hormone, evidenced by a low TSH (generally < 0.1) can have a deleterious effect on the heart and possibly bones. TSH has long been considered to be a potential stimulator of thyroid cells. However, there is no good evidence that an extremely low TSH is beneficial in preventing thyroid cancer recurrence.

8. Why do thyroid cancer patients take a relatively high dose of hormone replacement?

   Drucker (July 1/07)

   The principal aim of thyroid hormone replacement in patients with thyroid cancer is to maintain the TSH at a low and generally suppressed level. Several studies clearly demonstrate that a suppressed TSH correlates with improved survival in patients with well differentiated (papillary and follicular) thyroid cancer (Associations of Serum Thyrotropin Concentrations with Recurrence and Death in Differentiated Thyroid Cancer. J Clin Endocrinol Metab. 2007 Apr 10; [Epub ahead of print].) Accordingly, thyroid cancer patients will require doses of thyroid hormone that are often somewhat higher than those required simply to keep the TSH in the normal range. Following radioactive iodine, L-thyroxine is started, often the next day, and a TSH and thyroglobulin are obtained about 4-6 weeks later to ensure that they are both low. Occasionally patients will also receive T3 (Cytomel) for a week or two after the radioactive iodine treatment. There have been no randomized studies to determine whether we should aim for a TSH that is undetectable, versus a TSH of 0.1 or 0.2, and the precise TSH target level should be a matter of discussion between physician and patient. This area remains a matter of debate and discussion in the endocrine community, as illustrated in J Clin Endocrinol Metab 1999 Dec;84(12):4549-53 Levothyroxine suppression of thyroglobulin in patients with differentiated thyroid carcinoma.

9. Can one be allergic to Levothyroxine? Can one be allergic to one brand, but not the other?

   Ezzat (June 1/05)

   There are experimental molecules that look like T4 (thyroxine) or T3 tri-iodothyronine) however whether they would result in the same allergic reaction is not known. Generally speaking, true allergies to thyroid hormones are rare. The patient might be advised to consult with a clinical immunologist regarding assessment and possible desensitization to thyroid hormone.

10. What are the Canadian specifications for the bio-availability of the active Ingredient (ie. T4) within each tablet of Levothyroxine?

    Gascoigne (Dec 1/07)

    Health Canada finally got back to me.  The specifications required for the manufacturing of levothyroxine is that each batch must be between 90 and 110% of the labelled quantity.  For example, when making a 100 microgram tablet, the tablet must contain between 90 and  110 micrograms of levothyroxine.  You have to remember that we are dealing with percentages so for a 50 microgram tablet the specifications are that each tablet must contain between 45 and 55 micrograms.  These rules were made because with current manufacturing practices/technology it is not possible to make every tablet “exactly” right, but it ensures some accountability.

    At present Health Canadais not going to change these requirements, and the manufacturers of Eltroxin® and Synthroid® have not been notified of any upcoming changes.

    I tried to obtain some information on how quickly the different brands of levothyroxine degrade, but the manufacturers told me this was proprietary information that they could not share with me.

    Levothyroxine is sensitive to light and heat so in theory it may be a good idea to obtain smaller quantities when ordering your prescriptions, especially if the medication vial is kept on the kitchen counter.  However, if a person is able to protect it like a pharmacy can (i.e. pharmacies have rules governing temperature regulation/ drug storage) it may not make a big difference. 

    The only information I could find regarding patient’s asking about the expiry date of the levothyroxine being dispensed to them from pharmacies is to make sure when ordering a 3 month supply of the medication that the stock bottle in the pharmacy does not expire in 2 months (Such a bottle may still be on the shelf at the pharmacy).  In this scenario the last month of drug usage may not be providing the best potency.  In general, asking for the expiry date (i.e. best-before date) may not be too useful because you do not know the starting potency of the current levothyroxine drug batch you are receiving (i.e. a batch can contain 90% of the labelled dose or 110%- you cannot tell and the manufacturer will not disclose this).

    This was a difficult question to answer as the companies did not want to give me any information in fear that I would recommend one brand over another.  I hope this information is helpful.  If you need any clarification please let me know.

11. Should one be concerned that supplies of Levothyroxine will ever running low?

    Cheng (Sept 1/07)

    The half-life of thyroid hormone is 1 week. Therefore, it takes about 6-8 weeks for all the thyroid hormone to be gone from your body once you stop taking thyroid medication. The symptoms one would have would be similar to withdrawing from thyroid hormone for testing -- tired, weight gain, constipation, dry hair etc. For an extended period of time, it can have severe effects on all the organ systems and one could go into "myxedema coma". This is now exceedingly rare because hypothyroidism is readily diagnosed and treated.

    The good news is that thyroid hormone is manufactured almost everywhere in the world so I do not foresee ever having a supply issue. In the case of a disaster whereby shipments were interrupted for some reason, may be worthwhile to have 6 weeks’ worth on hand. Having said that, I would not "hoard" away thyroid hormone because there is an expiry associated with them

12. Since ‘Abbott Laboratories Limited’ manufactures Synthroid, why does it say “Flint” on my tablets?

    Gascoigne (Feb 1/06)

    In the past in Canada, Synthroid was manufactured by a company called "Flint" Pharmaceuticals. They branded the tablet by marking it with their company name.

    As time went by Flint was bought out by a company called Boots, who were then purchased by Knoll who were subsequently purchased by Abbott Laboratories, Limited.

    After each purchase, the companies did not change the tablet makings. Health Canada does not require the tablets to say "Synthroid" on them. In addition, changing the tablets would cost the company money as they would have to invest in new machinery and amend the product monograph.

    Editors Note:  Recently we noticed that Synthroid pills are now marked with the word 'Synthroid'.

13. Which is better Synthroid or Eltroxin?

    Gascoigne (Dec 1/06)

    Thank-you for the question. This is actually a very popular question: Which is better Synthroid or Eltroxin? They are both very good sources of levothyroxine manufactured by reputable companies. They are also both made under strict quality control guidelines. One brand is not "better" than another ... however they are not exactly the same.

    A Synthroid 0.1mg tablet contains: 100ug levothyroxine sodium, acacia, confectioner's sugar, D&C Yellow No.10, FD&C Yellow No.6, lactose, magnesium stearate, povidone and talc.

    An Eltroxin 0.1mg tablet contains: 100ug levothyroxine sodium, acacia, Colorcon yellow, cornstarch, lactose and magnesium stearate.

    Although the active ingredient (i.e. levothyroxine) is exactly the same in each of the brands, the non-medicinal or "filler" ingredients are slightly different. In theory, this can result in very small differences in absorption of levothyroxine. For the vast majority of patients taking thyroid medication this usually presents no difficulties. However, a patient being treated for thyroid cancer needs to keep his/her TSH very tightly controlled so a small change for these individuals may make a noticeable difference and the TSH level should be tested if the brand is changed.

    What does this mean? Should one only use Synthroid or only use Eltroxin brands? It means that once a stable dose has been found for you, one which produces the desired TSH, you should stick with that tablet... whether it be Eltroxin or Synthroid. You do not, for example, want to be taking Synthroid 0.1mg one week and Eltroxin 0.1mg the next. Stick with the brand that produced the best TSH for you.

    Because Synthroid and Eltroxin are not available in the same strengths, someone whose dose is being changed may be required to change brands. That is okay. For example, a person on Eltroxin 0.05mg would be required to switch to Synthroid 0.088ug if the doctor thought that 88ug was the best dose for that person.

    Synthroid is available in the following strengths: 25ug, 50ug, 75ug, 88ug, 100ug, 112ug, 125ug, 137ug, 150ug, 175ug, 200ug and 300ug.

    Eltroxin is available in the following strengths: 50ug, 100ug, 150ug, 200ug and 300ug.

    I hope that was helpful. With respect to the allergy question, the only experience I have with levothyroxine allergies are in people who are allergic to the colouring ingredients added to the tablets (i.e. yellow or blue dye allergies). For these individuals, we created their dose by using the 50ug tablets which are dye free."

    Editor’s Note: For more information on switching Levothyroxine brands for thyroid cancer survivors, see Dr. Michael Tuttle’s article in Thyroid Today: Levothyroxine Bioequivalence and Its Impact on Treatment of Thyroid Cancer Patients

14. Are Eltroxin and Synthroid interchangeable?

    Ezzat (June 16/05)

    The question posed is an important one. I believe that it is best for patients to stick with the same brand of thyroxine preparation. Mixing between brands may contribute to fluctuating blood levels despite the same dose. Patients should know exactly the brand and dose they are taking when they go to see their physician.

    Ain (June 16/05) quoted from a ThyCa Patients Forum posting

    I am adamant that all of my patients take BRANDED levothyroxine and NOT take generic levothyroxine pills. The choice of a brand (in the US: Synthroid, Levoxyl, Levothroid, Unithroid) is not critical, as long as each refill uses the same brand. I am convinced that the small differences in levothyroxine content and bioavailability between the same dosages of different brands (and particularly with generics) can be sufficient to make the difference between having a suppressed TSH without symptoms and a non-suppressed TSH or a suppressed TSH with thyrotoxic symptoms. Nearly all of my thyroidologist colleagues have provided testimony to the FDA that their current regulations regarding generic substitution are based on faulty and inappropriate data or concepts. This problem is not so significant for the many patients with simple hypothyroidism, taking levothyroxine preparations to keep their TSH in the normal range; however, it is very significant for thyroid cancer patients who need to balance themselves on the fine edge of TSH suppression.

     

    Editor’s Note: For more information on switching Levothyroxine brands for thyroid cancer survivors, see Dr. Michael Tuttle’s article in Thyroid Today: Levothyroxine Bioequivalence and Its Impact on Treatment of Thyroid Cancer Patients

15. How should one store their Levothyroxine (T4)?

    Gascoigne (June 16/05)

    The best rule to follow for storing thyroid medications:

    • Store medication at controlled room temperature between 15-30C. Protect from light and moisture.

    • It is best not to store medications in the bathroom or kitchen. After taking a hot shower, or cooking a lovely roast, the kitchen and bathroom can be the hottest, and most humid, rooms in the entire house. It is also a good idea to keep medications in drawers or cupboards; leaving medications exposed on shelves maximizes their exposure to light.

    If one is unable to follow these rules, one should limit the on-hand supply of medication that they have at home. For example, instead of ordering a 3-month supply of medication to store at their home, only order a 1-month supply. It is less likely that a medication’s potency will decrease after 30 days of light exposure, for example, versus 90 days.

     … and remember to always store your medications safely. Use child resistant vials and keep the medication out of reach of your children and visiting children

16. What should patients be aware of in regards to interference of vitamins/minerals with replacement hormone absorption?

    Ezzat (Mar 1/06)

    The concern here is that vitamins that contain calcium can interfere with thyroid hormone absorption which can be reflected in erratic TSH measurements. This is an important source of TSH variation. In addition, there is a much smaller contribution from diurnal influences where TSH levels fluctuate within a narrow range depending on time of day.

    It is best to separate taking the thyroid pills from any pills, particularly, vitamins/calcium by 2 hrs or more. If in doubt, consult with your treating physician and/or pharmacist.

17. For those changing homes from one part of the globe to another, how does one find a comparable dose of levothyroxine when the name brand they are used to taking, is unavailable in their new location?

    Gascoigne (Oct 1/09)

    I think that this question highlights the concerns that many patients, and clinicians, have about switching from one brand of levothyroxine (LT4) to another.
    
    The American Association of Clinical Endocrinologists, The Endocrine Society and The American Thyroid Association have published a joint position statement about switching between the various brands of LT4 (reference 1). The paper highlights concerns that there are small differences between the various brands of LT4, but because LT4 requires precise dosing, these differences may affect some patients should their brand of medication be changed.
    
    This issue is not seen with many other medications because in most disease states precise dosing of therapy is not critical. The organizations are petitioning regulatory bodies, such as the FDA, to enforce stricter manufacturing practices for LT4 but are still waiting for a positive response.
    
    With this in mind, what happens if you are put in a position where you must change to a different brand of LT4? At this point, your only course of action is to switch to the other brand, at the equivalent dose, and have your TSH measured in 6 weeks. There may be a small difference between the brands, but the only way to find out if it is a big enough difference to affect your therapy is to monitor your TSH for a change. If there is a change then there will need to be an adjustment of your medication.
    
    Reference:
    http://www.thyroid.org/professionals/advocacy/04_12_08_thyroxine.html
    
     

18. What special precautions need to be taken when travelling with replacement hormone (T4) and other medications?

    Chui (July 1/07)

    Synthroid and/or Eltroxin (thyroid hormone) are fairly stable, oral formulations and as such, do not have special handling requirements, other than the usual precautions when handling solid, oral medications. Ideally, the tablets should be stored between 15C- 30C, away from light and moisture. Patients who have been on long-term therapy and have achieved steady levels of the thyroid hormone should not anticipate any issues related to extra physical activities over a short period of travel.

    In general, the following tips may be helpful when it comes to traveling with medications over the summer months:

    • Pack an extra supply of your medication in case you are away for longer than expected. Take an extra 7-10 days supply of medications. For air travel, if possible, take half of the amount in your carry-on and the rest in your checked luggage. This will come in handy if your luggage is delayed or even lost.
    • Leave all medicine in its original, labelled container. Do not try to save luggage space by combining medications into a single container. Place medication containers in zip-lock bags to prevent the tablets or capsules from getting wet in case of accidental exposure to water or other liquids. This is particularly useful if you plan on hiking or camping.
    • If you require syringes for a medical condition such as diabetes, carry a supply to last your entire trip, as well as a medical certificate that states that they are for medical use. If you are traveling by air, please note that syringes are usually prohibited in carry-on luggage due to security concerns. Contact your airline before departure to verify their carry-on regulations.
    • If there are medications that need cooler temperatures e.g. insulin, certain vaccinations and/or injections, use ice packs to maintain the temperature until you can access proper storage facilities. This is especially important for long flights or car rides.
    • Carry a typed list of all your emergency contact numbers including your Family Physician’s and your Pharmacy’s telephone numbers.
    • Carry a typed list of all your medications and their dosages along with all your other important documents. Your medication profile can usually be obtained fairly easily from your regular pharmacy.
    • If you plan your vacation in advance, it would be wise to visit your doctor’s office to make sure you have all the necessary vaccines for your travel destination. Obtain a copy of your vaccination record from your physician and carry it with you in case you need to access it.
    • Take your medical and extended health care insurance cards with you. Ensure you have their toll-free number should you need to contact them from overseas.
    • Depending on your destination, you may want to discuss with your family doctor and/or pharmacist about medications you should have in case of certain emergencies. These may include antibiotics (e.g. for traveler’s diarrhea), painkillers, throat lozenges, antihistamines for acute allergic reactions, eye-drops, insect repellents etc.

     Editor’s Note:  If there was any chance your extra supply of levothyroxine was exposed to heat while you were on vacation, it might be wise to dispose of the extra tablets upon returning home.  As T4 degrades with heat, fresh tablets will help insure that you are getting the proper dose.

19. What do patients need to know about Levothyroxine (T4 -Synthroid and/or Eltroxin?

    Chui (Sept 1/07)

    Levothyroxine is a synthetic (man-made) version of the principle thyroid hormone, thyroxine (T4) that is made and released by the thyroid gland. Thyroid hormone increases the metabolic rate of cells of all tissues in the body. In the fetus and newborn, thyroid hormone is important for the growth and development of all tissues including bones and the brain. In adults, thyroid hormone helps to maintain brain function, food metabolism, and body temperature, among other effects. It is best to take the drug in the morning to avoid symptoms such as insomnia if the medication is taken at bedtime.

    Levothyroxine tablets usually are kept at room temperature, 15-30°C (59-86°F) in a light-resistant, tight container. Store the medication in the pharmacy bottle at room temperature away from sunlight and moisture. Do not store in the bathroom.

    The half-life of levothyroxine is about 7 days (i.e. it takes 7 days after you stop taking Levothyroxine to go from a certain concentration to half of that amount in your body). That is the reason why you only require taking it once daily. Levothyroxine has a sufficiently long half-life so that if the patient is unable to take medication by mouth for a few days, omitting T4 therapy will not be detrimental.

    It would be logical for some patients to prepare for an additional supply if they think they may be in a situation which would prevent them from obtaining replacement supply in a reasonable time frame. The extra supply should be stored properly as mentioned above for those unforeseen situations. If water damage is a concern, extra moisture protection may be provided if the light-resistant pharmacy bottle is placed inside a zip-locked plastic bag.

    When obtaining this extra supply, do not forget to ask for the expiry date and the manufacturer's lot number. A regular prescription label from the pharmacy would not include such information. This is normally not necessary when a regular prescription is dispensed. As part of the dispensing process, a member of the pharmacy team always examine and record of the expiry date for that particular medication in stock. This process allows the pharmacist to ensure the patient will receive good dating medication for the entire during of their therapy.

20. What other factors may cause the need for an adjustment in thyroid replacement?

    Cheng (Aug 1/08)

    The usual factors that can necessitate dose adjustment for thyroid medication are changes in weight, estrogen status, other medications or supplements. The weight issue is discussed above. As for estrogen status, pregnancy and menopause changes the body's amount of thyroid hormone binding proteins. This results in a change in the requirements for replacement. Usually in pregnancy, the dose needs to be increased by 25-50%, if not more. In menopause, the dose requirements usually go down, but this can be quite different from one person to the next.
    
     

21. Generally speaking, how much weight loss (or gain) necessitates an adjustment to a patient's Synthroid dosage?

    Cheng (Aug 1/09)

    According to the product monograph for thyroid replacement medication, the usual maintenance dose for a young, healthy patient with an under active thyroid is approximately 1.7 mcg / kg per day. In the case of thyroid cancer, we are often aiming for slight over-replacement.
    
    Therefore, the dose is usually closer to 2 mcg / kg per day. Given that smallest increment by which thyroid medication doses can change is 12-25 mcg, body weight would need to change by at least 5 kg before doses need to be changed. However, there is a significant amount of individual variability. Therefore, it is important that thyroid blood tests be performed if there is a weight change of greater than 5 kg.

22. What factors influence the need for an adjustment in thyroid replacement?

    Cheng (Aug 1/08)

    According to the product monograph for thyroid replacement medication, the usual maintenance dose for a young, healthy patient with an under active thyroid is approximately 1.7 mcg / kg per day.  In the case of thyroid cancer, we are often aiming for slight over-replacement.

    Therefore, the dose is usually closer to 2 mcg / kg per day.  Given that smallest increment by which thyroid medication doses can change is 12-25 mcg, body weight would need to change by at least 5 kg before doses need to be changed.  However, there is a significant amount of individual variability.  Therefore, it is important that thyroid blood tests be performed if there is a weight change of greater than 5 kg. 

    The usual factors that can necessitate dose adjustment for thyroid medication are changes in weight, estrogen status, other medications or supplements.  The weight issue is discussed above.  As for estrogen status, pregnancy and menopause changes the body's amount of thyroid hormone binding proteins.  This results in a change in the requirements for replacement.  Usually in pregnancy, the dose needs to be increased by 25-50%, if not more.  In menopause, the dose requirements usually go down, but this can be quite different from one person to the next. Therefore, it is important that thyroid blood tests be performed regularly when in the menopausal time period. 

    As for medications and supplements, some can interfere with the absorption of thyroid medication. 

    Therefore, it is important that you ask your pharmacist before starting any new medications or supplements and that you keep your doctor informed of any changes to your medications or supplements.