Does clenbuterol burn fat?

Short answer

No. In the first randomized trial in people, 2 weeks of clenbuterol changed body fat by 0.00 kg compared with placebo, while fitness dropped 7%. Among people who ended up in hospital, heart problems were the most common.

Does clenbuterol burn fat?
'Faster heart → more heat → fat burned' — does this formula hold?
Clenbuterol is an asthma and livestock drug, but it is known as a fat burner for contest prep and dieting. This article is not about how to use it; it only checks what actually happened in human studies.
Why is it known as a fat burner?
It started with livestock studies
A 1995 review noted that livestock given far more than the amount needed to open the airways gained more muscle and stored less fat. At the time, there were no human studies at all, and long-term effects on the heart had never been examined.
One dose in people
Calories burned at rest rose 21%
6 people took a single dose and were measured a little over 2 hours later. Calories burned at rest rose 21% and fat use rose 39%. At the same time, blood sugar rose 30%, insulin rose 130%, and thigh strength dropped 4%.
So does 2 weeks of it take fat off?
Body fat difference: 0.00 kg
In a randomized trial, 11 people took clenbuterol for 2 weeks and a placebo for 2 weeks. Lean mass (muscle and everything except fat) rose 0.91 kg, but body fat differed from placebo by 0.00 kg. Body fat fell by 0.3 kg in both periods alike.
Fitness dropped instead
Maximum oxygen uptake down 7%, exercise capacity down 4%
In the same trial, the maximum amount of oxygen the body could use fell 7%, and the ability to keep exercising until exhaustion fell 4%. Heart rate was 10 beats per minute faster 2 hours after a dose. Activity of a muscle enzyme that burns fat actually went down.
People who ended up in hospital
84% of 63 cases were admitted
An Australian poisons information centre recorded 63 clenbuterol exposures from 2004 to 2012, rising from 3 in 2008 to 27 in 2012. At least 53 people (84%) were hospitalized, mostly after using it for bodybuilding or weight loss. 1 person went into cardiac arrest.
Side effects centered on the heart
From a racing pulse to heart attack and death
At US poison centers, 11 of 13 users took it for weight loss or bodybuilding, and 2 had heart muscle damage. A review of 23 case reports covering 24 people found racing heartbeat, atrial fibrillation, heart inflammation, heart attack, heart muscle disease and death. Heart complications were the most common.
Summary: fat stays, the risk is to the heart
The formula stopped at 'more heat'
One dose raised calories burned by 21%, but after 2 weeks body fat differed from placebo by 0.00 kg. Fitness fell 7% instead, and heart problems were the most common reason people ended up in hospital. The fat-burning effect did not show up in human studies.