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Clenbuterol: Also known as Dilaterol, Spiropent or Ventipulmin

How Clenbuterol Works


Clenbuterol, nicknamed "clen," is the generic term for a nonsteroidal drug that was originally designed as a bronchodilator, used to treat chronic breathing disorders like asthma and obstructive pulmonary disease. However, given its powerful fat-burning properties, clenbuterol is also used by bodybuilders and professional athletes as a stimulant and/or weight loss drug.

Most commonly available in its salt form, clenbuterol hydrochloride, and sold under the trade names Dilaterol, Spiropent, Ventipulmin, this drug acts as a beta-2 adrenergic receptor agonist, meaning it stimulates beta-2 receptors. Clenbuterol also relaxes smooth muscles that line airways and helps them dilate (expand) to increase the amount of oxygen people and animals receive from each breath.

Aside from helping clear airways, other effects created by clenbuterol closely mimic adrenaline, a substance that's released in the body when one is feeling strong emotions like excitement or fear. But unlike adrenaline, which causes a multitude of physiologic reactions, clenbuterol is far more selective and mainly interacts with the beta-2 receptor.

This selectivity enables clen to produce specific adrenaline-like effects such as increasing core body temperature and raising metabolic rate, without also increasing heart rate by a substantial amount. Clenbuterol's stimulation of the beta-2 receptors causes the cells' mitochondria to heat up and produce more heat, thereby creating a thermogenic effect where more calories are burned, fat cells are stimulated and weight loss is more likely.

Beyond simple weight loss, clenbuterol leads the body to favor using stored body fat for energy over body protein. A 1987 study performed on rats concluded that the ratio of body protein to fat after clenbuterol treatment increased by over 50% in both normal and protein-deficient rats (1).

Obviously its ability to preserve muscle mass while burning fat makes clen a highly sought-after drug among bodybuilders. But it is also used by celebrities and the general population as well. So for anybody who's interested in this drug, let's move on to discussing clenbuterol's benefits, side effects, usage, dosage, comparisons to ephedrine and legality.

What are the Benefits of Clen?

The most-popular off-label use for clenbuterol is definitely weight loss. However, there are plenty of other benefits that clen can provide for humans and animals. But as you'll see below, humans and animals can experience different results (notably in building muscle) from taking this drug.

Appetite Suppression

While clenbuterol is often identified as a weight-loss drug, one of its lesser-known benefits involves appetite suppression. Research from 1994 concluded that clenbuterol's beta-2 stimulation has an effect on regulating feeding behavior (2).

Body Recomposition

Research has shown that clenbuterol can aid in animals' body recomposition, which is the process of simultaneously burning fat and building muscle. This is a difficult process because it requires precise caloric intake while burning enough calories through workouts. But a 1985 study involving Standardbred mares showed that clenbuterol usage can result in significant body repartitioning (3). After two weeks of being administered clen and undergoing regular exercise, the mares experienced a 15.4% drop in body fat percentage coupled with a 4.3% increase in fat-free mass.

Reducing Exercise-induced Asthma

Given its use as a bronchodilator for treating chronic breathing diseases, it only seems natural that clenbuterol would help reduce exercise-induced asthma. And a 1987 study confirmed this by revealing that clen protects against exercise-induced asthma without causing negative effects on the cardiovascular system (4). However, despite popular belief, this drug does not enhance cardiovascular efficiency in healthy individuals; in fact, a 1987 study showed that clenbuterol can reduce endurance and exercise duration (5).

Muscle Building

clenbuterol muscle building

Clenbuterol has been shown to have a positive anabolic effect in various species of animals. For example, clen increased the size of skeletal muscle fiber in rats in utero (6). Another study involving rats on a protein-restricted diet revealed that clenbuterol can hasten the recovery of muscle mass following malnutrition (7). There has yet to be any published research that links clenbuterol to being directly responsible for muscle enlargement in healthy humans (8). However, human studies do suggest that long-acting systemic beta 2-agonists can increase muscle size in specific muscle fibers. But this long-term effect may be so gradual that it goes unnoticed in healthy users.

Weight Loss

This drug can help provide dramatic weight-loss results in a short period of time. Unfortunately, there is a severe lack of human research in the scientific community regarding clenbuterol weight-loss effects. But there are numerous clenbuterol reviews across the internet that boast of this drug's notable fat-burning capabilities. Animal studies, such as the previously mentioned one involving mares, offer concrete proof that clenbuterol results include significant fat loss. Research performed on rabbits provides more evidence that clen can reduce body fat percentage in animals (9).

What Side Effects does Clenbuterol have?

While clenbuterol offers many benefits to users, it also comes with some harsh side effects, especially in certain individuals and when dosage is increased. The easiest way to avoid/lessen side effects is to reduce clenbuterol dosage. Many bodybuilders also choose to supplement their clen dosage to reduce side effects (discussed later). Below you can see some of the commonly reported problems with taking this drug.


Many clenbuterol users have reported terrible anxiety attacks when on the drug. For example, one person in this EliteFitness forum thread reported having such bad anxiety that their doctor prescribed them an anti-anxiety medication called Cipralex.

Cardiac Hypertrophy

One possible side effect of clen is cardiac hypertrophy, or the thickening of the heart muscle and subsequent decrease in size of the left and right ventricles. A study performed on treating left ventricular systolic dysfunction actually showed that clenbuterol aggravated the problem, whereas estrogen had a much-more positive effect (10).

Hypertension (Increased Blood Pressure)

Another dangerous clen side effect is increased blood pressure. Given that hypertension can eventually lead to serious problems, including heart attack, kidney failure and stroke, it's important to monitor blood pressure when using this drug.

Increased Heart Rate

While clenbuterol doesn't increase heart rate as much as adrenaline, the natural substance that it mimics, this is still a side effect that users need to worry about. So it's recommended that users monitor their heart rate to ensure that it stays within a safe range (60-100 resting BPM).


Like many powerful stimulants, clen can keep users up at night, especially when used in the evening. That said, many people take this drug in the morning to avoid insomnia.

Muscle Cramps/Taurine Depletion

In a four-day study involving rats and clenbuterol, urinary and liver taurine were significantly reduced in the mice (11). And a depletion of taurine can lead to severe muscle cramps, especially during workouts. So many bodybuilders who use clenbuterol often supplement it with taurine, magnesium, potassium and heavy water consumption to combat this side effect.


Given that clenbuterol raises the body's core temperature, sweating is a very common byproduct of taking this drug. Again, drinking plenty of water throughout the day is a good practice because it regulates body temperature and helps minimize sweating.

Who uses Clenbuterol?

Despite the fact that clenbuterol has not been approved for human usage in many countries (even as an asthma drug), it is widely used across the world as a weight-loss aid. When reviewing two U.S. poison control centers, a 2013 study noted that 11 of the 13 cases involving clenbuterol stemmed from bodybuilding and/or weight-loss use (12). Even in countries where it's illegal, clen remains popular among athletes, bodybuilders, celebrities and for enlarging livestock.

Asthma Medication/Horse Racing

Clenbuterol is approved as a therapeutic drug for treating asthma in Bulgaria, China and Russia. However, despite its usefulness as a bronchodilator, clen has not been approved for treating human breathing disorders in many other countries.

In Australia, most of Europe and the U.S., this drug can legally be used to treat breathing problems in horses. As Dr. Bob Judd from points out, though, some trainers have also illegally used clenbuterol as a performance-enhancing drug for race horses under the assumption that it delivers more oxygen. However, Oklahoma State's Dr. Michael Davis studied this subject and determined that clen has no performance-enhancing effect on horses.


Clenbuterol has become a very common drug in the bodybuilding community, thanks to its ability to induce fat loss while preserving muscle mass. A 2014 study performed on clenbuterol toxicity concluded that bodybuilding is the most-cited use of the drug among those hospitalized with severe clen side effects (13). But despite the risks and side effects associated with this drug, it still remains popular among bodybuilders.

Considering the lack of legitimate clenbuterol studies performed on humans, the bodybuilding world remains one of the best (though not always credible) sources for information on the subject. Forums, such as the one here at, are often referred to for those seeking info on how to effectively use this drug for fat loss.

In many cases, bodybuilders cycle other drugs like Cytomel (T3) with clenbuterol to enhance fat-burning effects. These are commonly called "cutting" cycles, and they are sometimes run before a competition to promote a lean, vascular onstage look. Bodybuilders also add clenbuterol into anabolic steroid cycles to keep their weight down while trying to increase muscle mass/strength. This is another area where little scientific research has been done on humans. However, a 2010 study performed on paraplegic mice revealed that clenbuterol and testosterone propionate used together are more effective at reducing muscle atrophy than testosterone alone (14).

Knowledgeable bodybuilders also use ancillaries during a clenbuterol cycle to minimize the previously discussed side effects. Magnesium, potassium and/or taurine are often used for on-cycle support to prevent painful muscle cramps. It's also suggested that clen users drink more water than usual to counteract the excessive sweating that can occur on a clen cycle.

Most suggestions on how to use clenbuterol for weight loss come through anecdotal evidence from bodybuilders who've used the drug. So, referencing threads from the EliteFitness forums, let's examine some different aspects of human clenbuterol use, including dosage, a sample cycle, post-cycle therapy, expected results and common forms of this drug.

Clenbuterol Dosage

Dosing is largely dependent on a user's clenbuterol experience, sex and how well their body tolerates the drug. An oft-recommended starting clen dosage for male beginners is 20mcg per day. And, as discussed in this forum thread, men can increase their daily dosage to 60-80mcg if the side effects aren't too unbearable. Experienced users will dose anywhere from 100-140mcg per day. As for female users, 10mcg is a commonly recommended starting dose, while many women will go up to 40-60mcg daily with experience.

Clenbuterol Half Life

Clenbuterol's half life, or the amount of time it takes for the drug's effectiveness to fall to half of its beginning value, is around 26 hours. Clenbuterol is detectable in the blood for 48 hours after being taken (15). Both of these points are highly important to bodybuilders because they base dosage frequency on much of a drug is still active in their system. The key is to keep a steady stream of clen running in the body to experience enhanced fat-burning effects.

Clenbuterol Cycle

When running a clenbuterol cycle, a typical recommendation is to take this drug for two weeks, followed by a two-week break. The reason why is, due to clenbuterol saturating beta-2 receptors, the drug loses its fat-burning benefits over time. Taking a break allows these receptors to clear out and move closer to their "clean" pre-drug state. So a standard clen cycle sees bodybuilders use a 2-week-on, 2-week-off format for 6-10 weeks. Below you can see a sample clenbuterol cycle in this format, where the user tapers at the end to reduce their body's post-cycle shock:



Cytomel (T3)





40-120mcg (w/ taper down to 40mcg)












40-120mcg (w/ taper down to 40mcg)


Post-cycle Therapy

When using anabolic and androgenic steroids (AAS), experienced bodybuilders undergo "post-cycle therapy" (PCT) to restore their hormone levels (notably testosterone) to a healthy range after a steroid cycle. But as mentioned in the introduction, clenbuterol is not a steroid, nor does it drastically alter vital hormone levels like AAS. Therefore, no PCT is needed when using clenbuterol on its own. However, when one uses clen in conjunction with AAS, they do need to research and run a proper PCT. You can view this forum thread to see a discussion on PCT when clen is taken with steroids.

Clenbuterol Results

clenbuterol results profile

The results of a clen cycle will vary greatly depending upon one's diet, dosage, cycle length and experience. Even still, it's not uncommon for bodybuilders to report a weight loss of 6-10 pounds after a 6 to 10-week clen cycle.

Where to buy Clenbuterol

Considering that clenbuterol is illegal for human consumption in many countries, it's often purchased on the black market. And when people buy clenbuterol, it usually comes in pill or liquid form, with spray form also being available, although less common. Those who buy clenbuterol online must be careful because not all products are totally legitimate or effective.

Comparisons to Ephedrine

Given that ephedrine and clenbuterol are both sympathomimetic amines that work as stimulants, appetite suppressants and weight-loss aids, they naturally draw comparisons in the bodybuilding community. Here you can see one a debate involving clenbuterol vs. ephedrine for fat loss. Most contend that clenbuterol is the more-powerful weight-loss drug, but its side effects and standard 2-week-on, 2-week-off cycle diminish its effectiveness.

Ephedrine, a stimulant that bodybuilders sometimes use with aspirin and/or caffeine to promote weight loss, isn't as powerful of a fat burner. But on the positive side, ephedrine doesn't come with as harsh of side effects and can still provide significant results. Case in point, 2013 research showed that ephedrine (combined w/ caffeine) caused an average weight loss of 5.9 pounds in test subjects over a 24-week period (16).


clenbuterol britney spears

In the mid-2000s, various mainstream news outlets reported that celebrities were using clenbuterol for weight-loss purposes. Britney Spears, Lindsay Lohan, Nicole Ritchie and Victoria Beckham were some of the names that surfaced during this period as celebrities using clenbuterol. A 2007 headline from The Sun exclaimed "Britney on Horse Drugs," in reference to her using the fat-burning drug. The Independent also reported on this phenomenon, quoting a popular gossip site named Popbitch with the following:

"LA's current concentration-camp look isn't just the result of cocaine and eating disorders. Everyone's doing Clenbuterol. Prescribed as an asthma medication, [it] is taken by body-builders and now weight-watchers for its amazing fat-burning qualities...ever wondered why celebrities always seemed to be hospitalized for asthma, dehydration and exhaustion?"

While celebrity clenbuterol use is rarely discussed in mainstream publications these days, it's unclear if this is because the drug's popularity faded among Hollywood's elite, or if it's simply no longer a hot story.


Because clenbuterol can accelerate growth and lean muscle mass when administered to animals in high doses, some farmers have used the drug on livestock. However, given a number of negative incidents around the world, most countries ban the use of clen on livestock raised for human consumption.

Nevertheless, there are still farmers who break the rules in order to raise lean meat at a faster rate. In China, where clen dosage in livestock was banned in 2002, government officials issued a warning about eating their country's meat to athletes competing in the 2008 Beijing Olympic Games (17). Following the Summer Games, 28 American athletes were tested for the drug, with 22 positive tests (79%) turning up, indicating that the meat contamination problem still exists.

China isn't the only country that's had an issue with clenbuterol use in livestock. In Spain, 34 people were arrested in 2010 in connection with an illegal clenbuterol ring that supplied the drug for cattle-raising, horse-racing and sports purposes. In Catelona, there were once 113 reported instances of clenbuterol poisoning, with over 50% of the affected reporting symptoms of headaches, muscle tremors, myalgia and tachycardia (18).

One of the most-famous instances of clenbuterol poisoning involved the Fédération Internationale de Football Association (FIFA) finding that 109 athletes at the FIFA U-17 World Cup 2011 tested positive for clen (19). The football organization then determined that contaminated meat in Mexico was the culprit for the large number of positive drug tests. Another incident in 2011 saw five players from the Mexican national football team test positive for clenbuterol; these players were later cleared on grounds that they ate contaminated meat.

Clenbuterol for Sports

Considering how clenbuterol can preserve muscle mass while simultaneously burning fat, and serve as a stimulant, it's a popular drug among athletes. There are reports dating back to 1995 that discuss clenbuterol's use as a performance-enhancing drug (20). Because of clen's ability to boost athletic performance, it is listed on the World Anti-Doping Agency's banned substances list. So any athlete who knowingly takes this drug is sure to draw a suspension and possibly other penalties.

Of course, much like the Mexican football players, other athletes have accidentally ingested clenbuterol through food or tainted supplements (21). Because of this, WADA once discussed changing the threshold for what constitutes a positive clen test. But in 2012, they decided that there would be "no plan to introduce a threshold level for clenbuterol." Instead, WADA has made great strides to improve testing and protect clean athletes from inadvertent doping (22).

Claiming that one has unknowingly taken clen through tainted food or supplements is a common defense among athletes. In some cases, such as one involving Australian cyclist Michael Rogers, athletes have been cleared of positive clenbuterol tests following an investigation. But in other instances, the suspensions have been upheld. Below you can see examples of athletes who have received clenbuterol-related suspensions:

2006, San Francisco Giants pitcher Guillermo Mota - Received a 50-game suspension while playing for the New York Mets. Mota tested positive for clenbuterol again in 2012, this time drawing a 100-game suspension.

2008, American swimmer Jessica Hardy - Tested positive for low levels of clen at the U.S. Olympic Team Trials. Hardy claimed innocence on grounds that she ingested a tainted supplement but still served a one-year suspension. The freestyle swimmer missed the 2008 Summer Olympics, but returned to the 2012 Olympics and won gold and bronze medals.

2010, Spanish cyclist Alberto Contador - Perhaps the most-famous example of an athlete being caught using clenbuterol, Contador blamed contaminated food on his positive test during the 2010 Tour de France, a race that he would go on to win. Nevertheless, he was stripped of his Tour de France title and 2011 Giro d'Italia victory and suspended from cycling for two years.

2012, Boxer Érik Morales - Suspended for two years after the United States Anti-Doping Agency (USADA) announced that Morales tested positive for clenbuterol. The champion Mexican boxer retired shortly after the suspension.

2014, Toronto Maple Leafs forward Carter Ashton - Suspended by the NHL for 20 games after testing positive for clen, which came from using an unprescribed inhaler.

2014, Korean swimmer Kim Ji-heun - Provided a positive test for clenbuterol in 2014, which resulted in a two-year suspension by the Korea Anti-Doping Disciplinary Panel.

2015, New York Yankees minor league pitcher Moises Cedeno - Suspended for 72 games after testing positive for clenbuterol.

Is Clenbuterol Legal?

According to, clenbuterol is legal for treating breathing problems in horses in Australia, the U.S. and many European countries. Furthermore, it's legal to buy clenbuterol in Canada and the U.K. for personal use; but both countries have outlawed supplying or selling the drug without a pharmacy license. China, Bulgaria and Russia allow their citizens to purchase clen as an asthma medication.

However, the majority of countries around the world have banned clenbuterol for weight-loss purposes. This has given rise to a large demand for black-market clenbuterol. That said, many people look for clenbuterol for sale at online pharmacies and websites.

Unfortunately, not all black-market sources for clenbuterol are legitimate, and some have poor quality control on their products. So anybody from a country where clen is illegal takes their chances by buying this drug from underground labs.

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Tags- Clenbuterol, Clenbuterol Dosages, Ketotifen, Bodybuilders, Steroids, Clenbuterol Hydrochloride, T3 Cytomix, Body Building