this in Ironman mag.

clenbuterol is a beta-2 adrenergic agonist,which means that it interacts
with adrenergic beta-2 receptors. In plain english,clenbuterol mimics the effects of catecholamines, such as epinephrine and norepinephrine.
Those hormones dilate bronchial tubes. Clenbuterol also dilates them,
explaining its primary use to treat asthma.
Although clenbuterol is available in other countries,such as mexico,under various trade names,it was never approved for use in the united states
and isn't likely to be in the future.The lake of interest by american drug
companies is related to clenbuterol's long half life in the body.Unlike other
beta-2 agonists used to treat asthma,which degrade in about six hours,
clenbuterol takes nearly two days to fully degrade.That considerably
increases the chances of side effects. What's more,clenbuterol isn't
superior to other available drugs for treating asthma.
Bodybuilders and other athletes became intrested in clenbuterol after
research showed that it promotes a gain in muscle mass and a loss of bodyfat in various animals.In their enthusiasm over those findings,
however, most athletes and "drug gurus" failed to read the small print:
the animals where given doses that would kill a human. Despite that considerable problem, clenbuterol quickly gained a reputation as muscle-building fat-loss drug. users soon realized that its active life could be measured in just a few weeks.The beta-2 receptors that clen interacts
with were extremely sensitive and shut down after about a month.when
that happened,clen did little or nothing.As the research continued, some
disturbing facts emerged.case reports pointed to clen as being the probable
cause of such adverse effects as tachycardia(rapid heartbeat), heart attack and even kidney failure in athletes who abused it. clen may have played a major role in the death of a popular pro bodybuilder a few years ago.that bodybuilder,who died from heart failure, was known to have injected large doses. Other animal studies showed that clen and aerobic exercise where a bad combination, since clen seemed to interfere with aerobic endurance.
some animals had sudden heart failure when given clen and forced to exercise. autopsies of the animals found an abundance of collagen in their hearts, pointing to production of scar tissue, which in the heart id a signal of failure.While much of the damage clenbuterol is ascribed to using large doses,
a recent study that used rats as subjects fount that even in low dosees it promotes celluar death in both the heart and slow-twitch muscles. The implication is that there's no such thing as a safe dose. since the drug dosen't
promote Muscle size increase in people and works only short-term for fat loss,
you can safely conclude that there's no rational health reason for any athlete to use it.

long read. but hope to recieve some input.