I Recently read this on T Nation
Even so, with ephedrine, you do eventually reach the point where down-regulation of these receptors occurs and thus the effectiveness is greatly diminished. One of the reasons why T3 is thought to work so well with beta-2 agonists is simply the fact that it can cause up-regulation of these receptors. However, with T3, you have yet another drawback, that being of course, suppression of endogenous thyroid production. Once you discontinue using T3 you'll be in a hypothyroidal state for at least a month. During that month you'll gain fat at a rapid pace, even if you're consuming the same amount of calories as you were previously. (3-8)
Has anyone experienced this?