Here's another:
This was written by BigAndy over at Elite, was a good read and as far as I can tell seems fairly accurate with medical references. Good enough for me anyways ... so here it is:
Disclaimer
T3 is not a drug that should be taken lightly. It's a very potent thyroid hormone. Messing with your natural hormone levels is very dangerous and unpredictable. The potential for complications is very high, and abuse can lead to thyroid disease and low thyroid output not only immediately upon discontinuation, but also later in life.
There is no such thing as safe use of T3 outside of a medical setting. There is only "safer" use. Use at your own risk.
Introduction: What is T3 and what are the side effects?
This article is pushing 2000 words, so here's a link for anyone who's interested:
http://arbl.cvmbs.colostate.edu/hbooks/pathphys/endocrine/thyroid/index.html
What about T4?
Bodybuilders should not use T4. It's a much weaker drug designed for long term use in patients with chronic thyroid disease. 100mcg of T4 corresponds to 25mcg of T3 and offers equivalent thyroid support; however, this does not translate to equal weight loss benefits. It has made itself on sources' lists simply because it is widely available and extremely cheap.
Is T3 catabolic?
It may shock many people to know that T3 is NOT catabolic per se. Corticosteroids are catabolic drugs that attack muscle tissue directly; T3 does not. It is a very potent calorie burner and it does not discriminate between carbohydrates, protein and fat. Unlike DNP, it has no protein sparing properties. T3 is also more likely to burn muscle than fat in lean users (10-12% BF), but this can be said for any extreme drop in caloric intake and uptake such as starvation diets (Caloric intake <10 X BW).
Muscle loss can be avoided with the use of anabolic agents. T3's alleged catabolic properties have become legendary. Excessive amounts of T3 (more than 75mcg), will have a very strong calorie burning effect, and since some bodybuilder use 150 mcg, it's easy to see why such misinformation has been so prevalent. The average bodybuilder will not need several grams of steroids to counter a reasonable dose of T3. There is no need to use more than 75mcg-100mcg. Going beyond this dose will cause more harm than good, as massive doses of steroids need to be used to counter the muscle loss, further stressing the body for minimal, if any additional benefits.
I think I've lost 20 lbs of muscle!
T3 can also give your muscles an extremely flat look and very soft feel. This side effect of extreme glycogen depletion can have a very profound psychological impact in bodybuilders. It often feels and looks like muscle loss when it's simply a lack of muscle "pump" because of restricted blood flow to that area and depletion of glycogen stores in muscles. Generally, carbohydrate loading does not solve this problem. "Pumping up" (or training for that matter) brings more blood into the muscles and is a temporary albeit effective solution. Clenbuterol and certain steroids can offset the lack of muscle pump because these drugs tend to "harden up" users by bringing more blood into to the muscles.
Are steroids absolutely necessary on T3?
This is very dependent on the user. Diet must be flawless, only reasonable doses should be considered (50mcg) and the user must know his body to a tee. Those who don't know what that last statement entails should not even consider T3. This is a veteran drug and should not be used by bodybuilders who are new to the game or do not have a deep understanding of how there bodies react to certain foods and training philosophies.
T3 can be used alone or better yet with Clenbuterol without fear of muscle loss in overly fat people (20-25% BF). This is not recommended, however, since these people will generally return to overeating upon discontinuation of their cycle and may likely end up with more weight than they started with.
How should I eat on T3?
Protein should be kept at 1.5-2g per lb of bodyweight. The majority of protein should come from lean meats. Shakes can be used, but should not be heavily relied on as they are more likely to be turned into glucose and used immediately for energy. Caloric reduction should come from carbs and fat only.
What is T3 used for?
Fat-loss: The main use for T3.
Increase Nutrient Uptake: Not very well known, but this is a great use for T3. Doses between 6.25-12.5mcg do not shutdown endogenous thyroid output. T3 at this dose can be used to add LBM and help in keeping the fat off. When doses are kept at 6.25-12.5mcg, muscles are full and rock hard, and energy is through the roof. At these light doses, it's common for people to go to the bathroom 5-6 times a day because there bodies are making more efficient use of the food they eat.
Can I permanently shutdown my Thyroid?
Simply put, NO, it can't happen. Natural thyroid production will be completely shutdown for a good period of time after using T3, but it will eventually recover. Bruce Kneller posted this study on the Testosterone website:
N Engl J Med 1975 Oct 2;293(14):681-4
Recovery of pituitary thyrotropic function after withdrawal of prolonged thyroid-suppression therapy.
Vagenakis AG, Braverman LE, Azizi F, Portinay GI, Ingbar SH.
The pattern of thyrotropin secretion was analyzed in seven euthyroid women, before and after withdrawal of long-term thyroid hormone, by serial measurements of thyroid 131l uptake, serum thyroxine, tri-iodothyronine, and thyrotropin concentrations, and the response to thyrotropin-releasing hormone. During exogenous hormone administration, 131l uptake was suppressed, and serum thyrotropin concentrations before and after administration of thyrotropin-releasing hormone were undetectable.
After withdrawal of exogenous hormone, thyrotropin secretory function was transiently impaired, as indicated by undetectable basal thyrotropin concentrations together with absence of response to thyrotropin-releasing hormone, and subsequently by normal values of basal thyrotropin concentration and normal responses to releasing hormone while serum thyroxine and tri-iodothyronine concentrations were subnormal.
Decreased thyrotropin reserve persisted for two to five weeks. Detectable values of serum thyrotropin (less than 1.2 muU per milliliter) and a normal 131l uptake usually occurred concurrently in two to three weeks. Serum thyroxine concentration returned to normal at least four weeks after hormone withdrawal.
Basically, it is extremely important to eat cleanly and keep up with cardio for at least 4 weeks and up to 6 weeks following a T3 cycle. It's also very important to ramp down properly and not use any drug that have an effect on metabolism and thyroid function, i.e. Clen, Ephedrine, Steroids, DNP, T2…
Calories should be kept in check, even lowered in some cases, and High Intensity Cardio is a must; at least 20mins, 3times a week. L-Tyrosine can be used at 1-3g a day to help thyroid function, but its effectiveness is debatable.
Switching to a higher carb, lower fat and lower protein diet is crucial in helping your thyroid bounce back after a cycle. A three-day carb up would be a good idea following a T3 cycle. This study demonstrates how important carbohydrates are for normal thyroid function. (Note: Some people seem to think of carbs as Lucky Charms and toast when there are far better carb choices that won't make you look like the Michelin Man.)
Dietary-induced alterations in thyroid hormone metabolism during overnutrition.
Danforth E Jr, Horton ES, O'Connell M, Sims EA, Burger AG, Ingbar SH, Braverman L, Vagenakis AG.
Diet-induced alterations in thyroid hormone concentrations have been found in studies of long-term (7 mo) overfeeding in man (the Vermont Study). In these studies of weight gain in normal weight volunteers, increased calories were required to maintain weight after gain over and above that predicted from their increased size. This was associated with increased concentrations of triiodothyronine (T3). No change in the caloric requirement to maintain weight or concentrations of T3 was found after long-term (3 mo) fat overfeeding. In studies of short-term overfeeding (3 wk) the serum concentrations of T3 and its metabolic clearance were increased, resulting in a marked increase in the production rate of T3 irrespective of the composition of the diet overfed (carbohydrate 29.6 +/- 2.1 to 54.0 +/- 3.3, fat 28.2 +/- 3.7 to 49.1 +/- 3.4, and protein 31.2 +/- 2.1 to 53.2 +/- 3.7 microgram/d per 70 kg). Thyroxine production was unaltered by overfeeding (93.7 +/- 6.5 vs. 89.2 +/- 4.9 microgram/d per 70 kg). It is still speculative whether these dietary-induced alterations in thyroid hormone metabolism are responsible for the simultaneously increased expenditure of energy in these subjects and therefore might represent an important physiological adaptation in times of caloric affluence. During the weight-maintenance phases of the long-term overfeeding studies, concentrations of T3 were increased when carbohydrate was isocalorically substituted for fat in the diet. In short-term studies the peripheral concentrations of T3 and reverse T3 found during fasting were mimicked in direction, if not in degree, with equal or hypocaloric diets restricted in carbohydrate were fed. It is apparent from these studies that the caloric content as well as the composition of the diet, specifically, the carbohydrate content, can be important factors in regulating the peripheral metabolism of thyroid hormones.
A post cycle crash is inevitable; this is the time when your diet really matters.
...contintued...
