Ketotifen is an anti-histamine used medically to treat bronchial asthma and allergies. It has a sedative and depressant effect on the brain. It acts by decreasing the release of histamine which is a chemical released when an allergic reaction occurs. Ketotifen blocks the action of histamine on special histamine receptors and reduces the nerve response when an allergic reaction occurs.
Histamine is the chemical in the body that causes the symptoms of an allergic (hypersensitivity) reaction. These can include inflammation of the skin, airways or tissues, rashes, itching and of the skin, eyes or nose, nasal congestion and narrowing of the airways. By blocking the actions of histamine, ketotifen may prevent and relieve the narrowing of the airways that occurs in asthma due to allergies.
However, bodybuilders are interested in the drug as it has been shown to inhibit the down regulation of the beta receptors, including the beta 2s that clen stimulates. 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. A dose of 2-3mg daily can upregulate 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 you can take about 30-40% less clen and it be equally effective.
No studies have been done to find the most effective dose though most users should find 3-4mg daily ideal, which can be split or taken in one sitting. Higher doses are likely to cause (sometimes severe) drowsiness and increase appetite.