*source: http://www.drrind.com/

If your adrenals can't handle the stress of the (thyroid) metabolic stimulation then you may harm them by taking thyroid in a dose that overwhelms them. In the short-run, you may feel better with the increased energy. In the long-run, you enter the world of adrenal fatigue which can be worse than thyroid hypo-function since you then get low thyroid AND low adrenal function. If it gets bad enough, you get purely adrenal symptoms and then wish for the good old days when it wasn't as severe. Fixing the adrenals is usually not such a big deal. Most people do fine and it usually only takes some adrenal support supplements. Once the adrenals are stronger, you can tolerate more thyroid support. The method I've developed and found most useful is to take daily temperature readings (see Metabolic Temperature Graph). This lets you know (by the pattern) if your adrenals are getting stronger and if your system is tolerating the thyroid support...thus you guide the process yourself once you understand the mechanism. Often, the temps rise as the body allows the thyroid to function better. If the temperature pattern becomes more stable but the temps do not rise, the thyroid may need a little help. Armour Thyroid or slow release T3 often help get things going if done gently and gradually. These medications (Armour thyroid, T3 or T4) are prescribed by your physician and you would work closely with him/her in this effort. If you only have a thyroid problem and the adrenals are fine, then the thyroid is all that needs to be addressed.

Q. What happens if I fixed the wrong one (thyroid vs. adrenals) first?

A.The thyroid and adrenals behave as if they have an inverse relationship with each other. A low function in one can look like a high function in the other. See the Metabolic Scorecard to get a better understanding of where your problem may lie. A mixture of both thyroid and adrenal problems provides the greatest challenge in treatment. If only the adrenals are supported, some adrenal symptoms may improve but the symptoms of hypothyroidism may become accentuated. Typically, these can appear as weight gain, fluid retention, rise in blood pressure, constipation, depression, etc. Conversely, if the thyroid is strengthened but the adrenals remain weak, we may see an improvement in hypo-thyroid symptoms but we may have an increase in adrenal fatigue symptoms such as anxiety, insomnia, hair loss, dryness, and unwanted weight loss. I have found that the improvement of hypothyroid symptoms tends to be short lived when the adrenals are not supported. For this reason, I tend to supported the adrenals first allowing the body’s metabolic state to return to optimal, then provide thyroid support only if needed.

How to take T3?A. Unlike T4, T3 is very fast acting. It can be slowed down by mixing it with a slow release substance. This is not commercially available but may be obtained from a compounding pharmacy (not a regular pharmacy). Because even the slow release T3 has a peak action of only a few hours, it is best to take it in divided doses. Thus a 15 mcg daily dose can be taken as 7.5 mcg approximately every 12 hrs. Or better yet, 5 mcg approximately every 8 hrs. The adrenals are less stressed if their metabolic environment is stable. According to pharmacological principles, a dose of medication will produce blood level of the medication that rises and then falls. If taken as 2 separate doses, the blood level is more stable. 3 doses produce an even more stable blood level, etc. Cytomel is an example of a fast acting T3. It produces a strong immediate effect (high blood level) which is followed by a weak effect (low blood level). It may require breaking up the dose into many small doses. Note that a stick of dynamite and a candle stick can generate the same amount of heat or energy. The difference between the two is the rate or speed that the energy is released.
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As we see from this, taking your t3 doses all at once will not be good. Despite the alleged 36 hour half life, the cytomel is absorbed quickly and you peak in a few hours. As the article says, too much t3 at once can cause too much stress on your adrenals which could likely be the reason for your fluctuations.