Clenbuterol is a widely used bronchodilator in many parts of the world. The drug is most often prepared in 20mcg tablets, but it is also available in syrup and injectable form. Clenbuterol belongs to a broad group of drugs knows as sympathomimetics. These drugs affect that sympathetic nervous system in a wide number of ways, largely mediated by the distribution of adrenoceptors. There are actually nine different types of these receptors in the body, which are classified as either alpha or beta and further subcategorized by type number. Depending on the specific affinities of these agents for the various receptors, they can potentially be used in the treatment of conditions such as asthma, hypertension, cardiovascular shock, arrhythmias, migraine headaches and anaphylactic shock. The text Goodman and Gillman's The Pharmacological Basis of Therapeutics Edition does a good job of describing the diverse nature in which these drugs affect the body:

`Most of the actions of catecholamines and sympathomimetic agents can be classified into seven broad types: (1) peripheral excitatory action on certain types of smooth muscles such as those in blood vessels supplying the skin, kidney, and mucous membranes, and on the gland cells, such as those of the salivary and sweat glands; (2) a peripheral inhibitory action on certain other types of smooth muscle, such as those in the wall of the gut, in the bronchial tree, and in blood vessels supplying skeletal muscle; (3) a cardiac excitatory action, responsible for in increase in heart rate and force of contraction; (4) metabolic actions, such as an increase in the rate of glycogenolysis in liver and muscle and liberation of free fatty acids from adipose tissue; (5) endocrine actions, such as modulation of the secretion of insulin, rennin, and pituitary hormones; (6) CNS actions, such as respiratory stimulation and, with some of the drugs, an increase in wakefulness and psychomotor activity and a reduction in appetite; and (7) presynaptic actions that result in either inhibition or facilitation of the release of the neurotransmitters such as such as norepinephrine and acetylcholine."

The drug clenbuterol is specifically a selective beta-2 sympathomimetic, primarily affecting only one of the three subsets of beta-receptors. Of particular interest is the fact that this drug has little beta-1 stimulating activity. Since beta-1 receptors are closely tied to the cardiac effects of these agents, this allows clenbuterol to reduce reversible airway obstruction (and effect of beta-2 stimulation) with much less cardiovascular side effects compared to nonselective beta agonists. Clinical studies with this drug show it is extremely effective as a bronchodilator, with a low level of user complaints and high patient compliance. Clenbuterol also exhibits an extremely long half-life in the body, which is measured to be approximately 34 hours. This makes steady blood levels easy to achieve, requiring only a single or twice daily dosing schedule at most. This of course makes it much easier for the patient to use, and may tie in to its high compliance rate. In spite that clenbuterol is available in a wide number of other countries however; this compound has never been approved for use in the United States. The fact that there are a number of similar, effective asthma medications already available in this country may have something to do with this, as a prospective drug firm would likely not find it a profitable enough product to warrant undergoing the expense of the FDA approval process. Regardless, foreign clenbuterol preparations are widely available on the U.S. black market.

In animal studies, clenbuterol is shown to exhibit anabolic activity, so it is obviously an attractive trait to the athlete. This compound is additionally a known thermogenic, with beta-2 agonists like clenbuterol shown to directly stimulate fat cells and accelerate the breakdown of triglycerides to form free fatty acids. Its efficacy in this area makes clenbuterol a very attractive, and today almost mandatory, pre-contest drug. Those interested in this drug are most often hoping it will impart a little of both benefits, promoting the loss of body fat while imparting strength and muscle mass increases. But as was well pointed out by a review published in the August 1995 issue of Medicine and Science in Sports and Exercise, the possible anabolic activities in humans are very questionable, and based only on animal data using much larger doses than would be required for bronchodilation. With such reports there has been a lot of debate lately as to whether or not clenbuterol is really anabolic at all. Some seem to swear by the fact that it builds muscle regardless, firmly sticking by "clen" as a great off-season or adjunct anabolic. To others such reports are confirmation that athletes have wasted valuable time and money on drugs that do not work as they are intended to by the user. This debate continues today, with many still using clenbuterol as a potential anabolic. With this in mind athletes will tailor their dosage and cycling of this product individually depending on which of the two "possible" results are more desired, and how much side effects are to be tolerated. The possible side effects of clenbuterol include those of other CNS stimulants, and include such occurrences as shaky hands, insomnia, sweating, increased blood pressure and nausea. These side effects will generally subside after a week or so of use however, once the user becomes accustomed to the drug. One would typically start a cycle by gradually increasing the dosage each day until a desired range is established. This process will minimize the unwanted side effects seen from the drug; which otherwise might be dramatic if a large dose is administered from the onset. Men generally end up in the range of 2-8 tablets per day, although some people do claim to tolerate even higher dosages. Women get by on less, generally 2-4 tablets daily. Very quickly, the drug will elevate the body temperature. The rise is not usually dramatic, perhaps a half of a Cegree or so, sometimes a little more. This elevation is due to your body burning excess energy (largely from fat) and is usually not uncomfortable. Now that it is working, the number of consecutive days clenbuterol can be used is believed to be dependent on the goal of the individual. To be clear, the athletic benefits of this drug will only last for a limited time and then diminish, largely due to beta-receptor down regulation. When using it for fat loss. the primary effect of the drug, it seems to work well for approximately 4-6 weeks. During this period users will want to constantly monitor their body temperature. We are assured clenbuterol is working by the temperature elevation. Once the temperature drops back to normal, clenbuterol is no longer exhibiting a thermogenic effect. At this point increasing the dosage would not be very effective, and a break for at least a few weeks should be taken before it is used again effectively. If one is looking for strength gains, clenbuterol appears to be effective for a much shorter period of time, around 3-4 weeks. This may be due to an absence of real anabolic effect, with the strength gain seen with clenbuterol possibly due only to the stimulant properties of the drug (similar to the strength boost seen by Ephedrine users). Again however, this is still debated.

Many competitors also find the fat burning effect of clenbuterol can be further enhanced by additional substances. When combined with thyroid hormones, specifically the powerful Cytomel®, the thermogenic effect can become extremely dramatic. This can be to a point that the athlete could shred exceptional amounts of extra fat during contest preparations, without a dramatic restriction in calories. Such a mix can be further used during a steroid cycle, eliciting a much harder look from the anabolics. These cutting agents can often greatly inhibit extra fat storage during the cycle, even when using strong aromatizing androgens. A clenbuterol/thyroid mix is also common when using growth hormone, further enhancing the thermogenic and anabolic effect of this therapy.