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.
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
Body Recomposition
Reducing Exercise-induced Asthma
Weight Loss

Side Effects-

Cardiac Hypertrophy
Hypertension (Increased Blood Pressure)
Increased Heart Rate
Muscle Cramps/Taurine Depletion

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. 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:
Week Clenbuterol Cytomel (T3)
1 40-100mcg 20-50mcg
2 40-120mcg (w/ taper down to 40mcg) 50mcg
3 Off 50mcg
4 Off 50mcg
5 40-100mcg Off
6 40-120mcg (w/ taper down to 40mcg) Off
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.

Categories: DNP & FAT LOSS
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