To understand how this all fits together, you first have to understand what high doses of T3 will do. To begin with, it will shut down your body’s production of T4, as well as the very little amount of T3 that it produces. The conversion of T4 is what provides the majority of your T3. As T4 is a storage hormone, it will remain in your body for a certain period of time, but once it clears you are left with only your artificial T3.
Now I'm sure you already knew this, so follow along with me. When you are hypothyroid, your body is not producing enough thyroid hormone. Guess what happens when you abruptly stop taking T3 and your body is not producing ANY thyroid hormone? That's right... the same result, only worse, since you have no thyroid hormone after the T3 has cleared your system.
Now I'm sure that I could find several examples and studies online, since I know for a fact that they exist, but right now I'm short on time and will post them when I have a chance. Besides that, you seem to be a smart guy, so I'm sure this has to make at least a little sense to you. I did however find this with a quick search and if you understand how low thyroid mimics hypothyroidism, you can put 2 & 2 together.
"In certain conditions, the thyroid becomes underactive and produces fewer amounts of its hormones, a situation called hypothyroidism. People with hypothyroidism have problems that reflect under activity of the organs of the body, resulting in symptoms such as fatigue, feeling cold, weight gain, dry skin, and sleepiness. When the levels of thyroid hormones become very low, the symptoms get worse and can result in a serious condition called myxedema coma."
Myxedema Coma
This implies a progression of symptoms over a period of time longer than the 2 weeks or less that studies show it generally takes for a healthy thyroid gland to return to full function. Thus, I'm not convinced that the alleged danger exists even in theory. I'm waiting for the studies and examples of healthy people without hypothyroidism who experienced myxedema coma as a result of abruptly stopping T3.
I'm also curious as to if in fact this happened (which I doubt), tapering off T3 would have prevented it.
In regards to your skepticism concerning the metabolism of drugs, it is a well known fact and I'm surprised that you would even question it. Thyroid hormone and your liver are two major factors in the metabolism of drugs. This why a hyperthyroid individual may need larger doses of a medication, while a hypothyroid individual may need less. When your body does not metabolize drugs properly, you are at risk of overdosing or building toxicity from the drugs remaining in your system at higher & higher levels.
"Thyroid dysfunction can influence the physiological disposition of drugs. Depending on the pharmacokinetic properties of the individual drug, changes in the rate of metabolism ranging from profound to moderate or negligible have been observed. Since renal function is also influenced by thyroid disease, changes in renal elimination of drugs which are excreted in the urine mainly as unchanged drugs have to be considered as another reason for altered drugs disposition in thyroid disease."
Drug metabolism in thyroid disease. [Clin Pharmacokinet. 1976] - PubMed result
Again, I've never heard of any credible stories of bodybuilders who suffered "serious medical consequences" including but not limited to drug overdoses or other ill effects as a result of abruptly stopping T3. I wonder what kind of drugs a healthy bodybuilder would generally be taking that would cause problems for them if they abruptly stopped taking T3. Again, healthy bodybuilders' thyroid glands quickly begin producing thyroid hormones once t3 supplementation is stopped. So, again, I'm skeptical of the theory and we still have no evidence or examples of this actually happening.
