I see a lot of newbie people trying to find good info on this so I thought it would be best to put it all in one place. I patched this from a wide range of sources as well as my own experience (also thanks to FONZ). This truly is a wonderdrug for BB. 

What Is It? 
Ketotifen is very safe antihistamine used extensively in Europe to treat bronchial asthma and allergies. It is also being studied as a treatment for colitis. When used for asthma, weight gain and an increase in appetite are among the most frequent side effects. Ketotifen also protects the cells in the stomach, small intestine and perhaps the rest of the gut from a number of toxins. A number of case studies suggest that it may be helpful treating skin problems such as acne. Ketotifen also reduces edema (swelling and puffiness caused by water retention) around sores. 

Ketotifen Studies 
German researchers have published data showing that ketotifen lowers tnf-alpha in the test tube. One study used ketotifen in combination with oxymethadone, a steroid like Megace that helps people gain weight, so it is hard to gauge what effect ketotifen had (the study notes a 14% reduction in TNF-alpha levels and weight gains of 11-12 pounds in less than four weeks). A larger placebo controlled study of this combination is underway. The other study used ketotifen by itself in eight patients with elevated TNF-alpha, (but no wasting). Taking Ketotifen for 12 weeks, these patients gained an average of six pounds, had increases in their body cell mass and reductions in their TNF-alpha levels. 

Side Effects and Toxicity 
Ketotifen is virtually non-toxic (although it is not advised for patients with epilepsy). People who took twenty times the recommended dose (in suicide attempts) suffered no serious consequences (other than embarrassment). Its primary side effects seem to be temporary drowsiness, dry mouth ,(and other mucuos membranes) appetite stimulation and weight gain. 

Dosing and side effects 
No studies have been done to find the most effective dose but the German researchers used 4 mg ED. Dan Duchaine (who discovered ketos use for BB) suggested 10mg ED but in my experience this much is not needed and makes u far too sleepy. I find that 3-4mg ED seems ideal. However, much higher doses have been shown to be quite safe with no adverse affects other than increased drowsiness and appetite – it will make u hungry for solid foods. You can take it divided in the day or all at once. 

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 up regulates 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 down regulate – 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 up regulate even severely shut down receptors within a week. 

It also means that you don’t need as much clen to get the same benefits. It seems u can take about 30-40% less clen and it be equally effective. FONZ posted that it also increases the number of receptor sites on the surface of the cell, allowing more clen to attach and perhaps this is the reason for the increased efficacy. Ketotifen also seems to lessen the sides of clen including the jitters. 

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. 

"Ephedrine is believed to have some direct effect on both alpha adrenoceptors and beta adrenoceptors, but AT THERAPEUTIC DOSES, ephedrine exerts its thermogenic effect almost entirely via stimulating noradrenaline release from the sympathetic nerve terminals [endings] . . . at least 40% of the [thermogenic] response is mediated by an atypical receptor, which is presumed to be the beta 3-adrenoceptor." 

from 
Liu YL, Toubro S, Astrup A, Stock MJ Contribution of beta 3-adrenoceptor activation to ephedrine-induced thermogenesis in humans Int J Obes Relat Disord. Sep;19(9). 678-685 

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