Ketotifen (Keto) is an H1-antihistamine. It is used orally as a medication to aid in the prevention of asthma attacks, and has also been used by many as a sleeping aid and appetite stimulant. Ketotifen is made popular by its ability to inhibit the down regulation of beta receptors caused by drugs like clenbuterol. Clenbuterol, albuterol, and Ephedrine used to be cycled on and off because they desensitize the various receptors they act on to produce their lipolytic effect. Ketotifen would therefore allow the use of these fat burning drugs for much longer periods. Ketotifen also (potentially) improves insulin sensitivity within muscle tissue.