Ketotifen and Clen
Clenbuterol is a beta 2 agonist which has a limited anabolic effect during its first few days of use and afterward is normally used to fight fat. At higher doses, however, it can be catabolic to muscle and it must be cycled on a 2 week on, 2 week of basis or the beta 2 receptors that clen binds to become saturated and down regulate.
Ketotifen's magic is that it upregulates the beta-receptors including the beta 2s that clen uses. As long as you are taking ketotifen, it will continue to clean these receptors, never allowing them to downregulate, even while on a heavy clen cycle. That means you can continue to take clen indefinitely without having to cycle off to regenerate the receptors. 2-3mg ED can upregulate even severely shut down receptors within a week.
Ketotifen and ECA
Perhaps an even better use for ketotifen is taking it with the ECA stack. While the thermogenic effect of ephedrine is not as potent as clen because it doesn't have a high receptor affinity, and it is not limited to beta-2 receptors. In fact it seems to have a good effect on beta 3 receptors as well, which act as a type of thermogenic messenger and over half of ephedrine effect is from beta-3 stimulation. Clen has almost no effect on beta 3 however. So by keeping the beta 2 receptors up, ketotifen can allow the benefits of continuous beta 2 and beta 3 stimulation from ephedrine.