Article by PartyBoy - MuscleTalk Moderator

What is Clenbuterol and what does it do?

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.

Clenbuterol side effects/possible implications?
Side effects are dose dependant, though most users will find that most tend to subside with persistent use. Caution is advised when employing the use of Clenbuterol in conjunction with other adrenoceptor agonists as side effects are likely to be cumulative. It is for this reason that it is generally not recommended to use ephedrine/ephedra (or ma huang) or the ECA stack (ephedrine-caffeine-aspirin) whilst using clen.

Common side effects of clenbuterol include:
Muscular tremors (especially hand shakes)
Muscular cramps
Increased appetite
Hypertension (high blood pressure)
Possible cardiac hypertrophy as clen also targets cardiac and smooth muscle fibres
Heart muscle necrosis has been demonstrated in animal studies

In view of the above side effects, it is obvious to assume that anyone with cardiac issues and/or hypertension should not use a stimulant such as Clenbuterol and caution must be observed by those already using similar compounds in the treatment of existing medical conditions. In addition, there is very little conclusive knowledge of the cardiac effects of supra-physiological dosages in humans.

Commonly used doses
It is well known that Clenbuterol use results in rapid down-regulation of beta 2 receptors. This is due to the powerful stimulatory effect of the drug. It is therefore pointless to use clen for long periods without a break. Some believe that a two day on, two day off dosing schedule will allow adequate potential for receptor up-regulation. However, I doubt this to be the case due to the relatively long half life of clen, resulting in continued stimulation even throughout the 'off' days. A much better regime would be a two week on, two week off cycle. Maximum plasma levels are reached around 2-3 hours after oral administration, and terminal half life at 34 hours (Zimmer, 1976).

A tapering up of dosages is recommended in an attempt to limit harsh side effects. Most commonly, a user will start by taking one 20mcg tablet on day 1, followed by an increase of one tablet on subsequent days. Subject to personal tolerance levels, a dosage of 140mcg (seven tabs) will be used by day 7, and this level should be maintained for the entire second week. It would be fruitless to exceed seven or eight tablets daily due to receptor over-saturation. There is no requirement to taper down.

For the next 'cycle' of clen (i.e. weeks 5 & 6), there is no requirement to taper up from one tablet as your tolerance level should now be known. As an example, if the user finished the first cycle of clen on 7 tabs, they could recommence at a slightly lower dose of 4 or 5, and taper up again from this level. Again though, the user should again limit their intake to 7 or 8 tabs daily.

During the two 'off' weeks, an ECA stack can be used as required. ECA will not cause such a pronounced down regulation and desensitization of the receptors, certainly not to the extent of clen. Ephedrine has a short half life in contrast to clen which results in times throughout the day where the betas will partially recover from stimulation by adrenaline and nor-adrenaline. Potency is also much weaker that that of clen, as it is not a specific agonist. Ephedrine is also thought to increase the conversion of endogenous/exogenous T4 to T3 through the activation of deiodinase enzymes responsible for this process. This is important as clen is known to slow the rate of T4 to T3 conversion. As a side note, some bodybuilders will use T3 concurrently with the Clenbuterol/ECA cutting cycle (together with certain anabolic/androgenic steroids no doubt!) in an attempt to at least maintain plasma T3 levels.

Cycles of Clen/ECA are normally limited to 12 weeks in total, though are often shorter.

Female dosages tend to be slightly lower than those of male users, with an upper limit of 80-120mcg (4-6 tabs).

Aside from its fat burning properties, Clen is often used as an anti-catabolic to maintain muscular gains following a steroid cycle. A dosage of 40mcg daily would be suited to this situation.

There is no particular requirement to split the dosage throughout the day due to the long half life. Most will take the full daily dose in the morning, though some prefer to take their dose just before bed in an attempt to avoid most of the side effects as they sleep.

Some user accounts suggest that splitting the dose may lessen side effects slightly. It is a trial and error process in essence, to ascertain which method suits you personally.

Muscular cramping
Cramping whilst using Clenbuterol is a fairly common side effect. This is most probably due to depletion of the amino acid taurine in the liver together with deficits in the electrolytes sodium and potassium, as well as inadequate hydration. Taurine helps stabilize cell membranes and prevent nerves from becoming over-excited. Some studies show that giving taurine supplements relieves painful muscle cramps. Japanese researchers found that the longer rats exercised, the more taurine they lost from their muscles (Matsuzaki et al, 2002).

Symptoms of cramping may be alleviated by:
Eating fruit particularly bananas
Ensuring adequate hydration
Taurine supplementation - 3-5g daily
Potassium supplementation - 200-400mg daily taken before bed on an empty stomach

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.

  1. Matsuzaki et al (2002). Decreased taurine concentration in skeletal muscles after exercise for various durations. Med & Sci Sp & Ex. 34(5):793-797.
  2. Zimmer (1976). Single and multiple applications and metabolite pattern of clenbuterol in man (author's transl). Arzneimittelforschung 26(7a):1446-50.


( En Español)