Clenbuterol (often referred to simply as ‘Clen’) is not a steroid, but a Beta 2 Sympathomitetic and central nervous system (CNS) stimulant. It is a specific agonist, stimulating the adrenergic beta 2 receptors. It is used in certain countries in a medical sense as a bronchodilator in the treatment of asthma, though not in the UK and USA, mainly due to its long half life.
Athletes and bodybuilders use the drug due to its thermogenic and anti-catabolic effects. This is down to its ability to slightly increase the body’s core temperature, thereby raising calorie (energy) expenditure. It is thought that a 1°F increase yields around a 5% increase in maintenance calories burned. Studies on livestock suggest that clenbuterol also has anabolic properties. However, this seems not to be the case in humans, thought to be due to the fact that humans lack the abundance of beta 3 receptors which increase insulin production and sensitivity.
Clenbuterol is dosed in micrograms (mcg/µg), most commonly in tablet form, though there are other forms of administration such as liquids, nasal sprays and injectables. Note: Although dosages are in microgram amounts, many manufacturers will list the active ingredient as milligrams (mg), so a tablet of 20mcg will be labelled as 0.02mg.