Hey norm - He is right in that T3 can be dangerous, and I think that's what stops most people from running with their cycles. Honestly, I haven't done any specific looking into the effects of certain doses of exogenous T3 with or without cycles of androgens. However, I will get some done on it tonight. I can however explain how T3 works to everyone else who will read this.
T3 (triiodiothyronine) is produced by the follicular cells in the thyroid gland. This is stimulated normally by in increase in both TRH (thyroid releasing hormone) and TSH (thyroid stimulating hormone) from the hypothalamus and anterior pituitary (respectively). What actually happens is that TRH will stimulate TSH which will in turn stimulate the production of both T4 and T3 from the thyroid glad, however about 90% of the thyroid hormone produced by the thyroid is T4, which is the inactive form. T4 can circulated in the blood, bound to thyroid binding globulin, for up to 7 days and it's sole job is to get to the liver or other peripheral tissues. Once here it can get off of the TBG and get inside of the cell where it will be changed into T3. The life of T3 once it is in the blood is much shorter than T4, it will last only 1 day. However, T3 is 10x more active than T4 and thus is the main thyroid hormone our bodies use.
The main effect of T3 in the body is to increase the BMR (basal metabolic rate). However, there are many other things that happen due to this. Thyroid hormones will increase both your cardiac output (the amount of blood your heart pumps out/min) and ventilation. This will lead to an increase in oxygen consumption as well as an increase in your metabolic rate. This increase in the metabolic rate is what gives you an increase in thermogenic response (i.e. feeling hot all of the time).
Another important aspect is that thyroid hormones are protein anabolic under normal conditions, but will become protein catabolic when the levels are high. (I don't know right now what level it is where they change from anabolic to catabolic.) This catabolism explains the decreased muscle mass and increase urea (removal of nitrogen) seen in people who pathologically have hypersecretion of T3 (hyperthyroidism diseases like Graves disease).
A 3rd important effect of thyroid hormones is that they are lypolytic (destruction of fat cells).So increased T3 will cause an increase in appetite from the increase in BMR, but also an increase in weight loss, due to the lipolysis.
Thyroid hormones will also increase synthesis of GH and Somatomediens (IGF-1, IGF-2, and IGF-3). However when T3 is hypersecreted it will increase production of Somatostatins which will inhibit both GH and IGF, as well as many other things.
Thyroid hormone is definitely essential to our bodily functioning. It does many wonderful things for us, that I believe can be augmented by raising the levels of T3 in our bodies (especially for bodybuilders). However, the problem becomes trying to decide how much to raise it and where the benefits stop and the problems begin. You also have to worry about what happens to your levels of TRH and TSH when you body no longer feels that it needs to make T3 or T4. Taking T3 orally will decrease both TRH and TSH, which will in turn shut down your natural production of T3. So you definitely need to go on T3 and come off of it in steps.
I can't tell you exact levels right now from my personal knowledge b/c I've never used it and have never done the research on my own to check out the numbers. However I can tell you what you will see in people who take too much thyroid or come off of it too quickly.
People that take too much T3 will show signs of - high BMR, proptosis (bug eyes), increased ventilation rate (leading to acidosis), sweating, increased appetite, weight loss, tachycardia (very fast heart rate), increased cardiac output, fine tremors, restlessness, nervousness, and emotional instability.
People who come off of T3 to quickly will show signs of - BMR decreased, leads to obesity, personality change, mental instability, lethargy, hair starts to fall out, skin becomes thick and dry, and poor skeletal muscle tone.
That's a long enough post for now. I am sure that there are holes in this as I am not using any sources. So please ask questions if you have them or point out where I have screwed up on this. Also, I am going to look into the dosage guides for T3. However, I know many other people on here have experience with T3 so please post those experiences here.
