Clenbuterol is Anabolic in Humans


by Anthony Roberts

Back in 2004 I wrote the first heavily researched article of my career. It was about Clenbuterol, and you can still find it in article forums and profile sections on most major sites. One of the most controversial points I made was that Clenbuterol is anabolic. At the time there was a pretty reasonable amount of animal data (rodents, horses, etc…) and I was fairly confidant saying that Clen has anabolic – or at least strongly anti-cabtabolic – effects in humans. Back when I wrote that article, and my subsequent book(s), there was no published medical data on the accrual of fat free mass in humans using Clenbuterol. And frankly, most bodybuilders who used the stuff were also using a lot of other stuff too.

Naturally, because there was no human data to support this notion, online steroid ”experts” rallied behind the notion that because there was no human data proving otherwise, Clen must not have that effect outside of animals. Anyway, a couple of studies have recently popped up in the US National Library of Medicine, that are new or were previously unavailable or unpublished. One is from all the way back in 1993, and was conducted in the UK, and seems to indicate that Clen helped patients regain muscle strength more quickly after orthopedic surgery:

Clenbuterol, a beta-adrenoceptor agonist, increases relative muscle strength in orthopaedic patients.

Clin Sci (Lond). 1993 Jun;84(6):651-4.
Maltin CA, Delday MI, Watson JS, Heys SD, Nevison IM, Ritchie IK, Gibson PH.
Rowett Research Institute, Bucksburn, Aberdeen, U.K.


1. The sympathomimetic agent clenbuterol has a muscle-specific anabolic effect in normal and wasted muscles from animals. This trial was designed to examine the effect of the drug on the recovery of muscle strength and area after open medial meniscectomy. 2. A double-blind, completely randomized, placebo-controlled study was carried out on 20 healthy male patients. Muscle strength and cross-sectional area were determined before and after surgery. Patients were treated with drug or placebo for 4 weeks postoperatively and there was a 2 week washout period. 3. The results suggest that, in the operated leg, clenbuterol treatment is associated with a more rapid rehabilitation of strength in knee extensor muscles; in the unoperated leg, knee extensor strength increased above the initial values after 6 weeks (P = 0.01). However, in terms of absolute strength the differences were not significant between the two groups. 4. It is concluded that the data lend support to the proposition that clenbuterol has therapeutic potential in the treatment of muscle-wasting conditions.

In this next study, patients with chronic heart failure were given Clenbuterol, and made some decent gains in muscle size & strength, as well as their lean mass to fat mass ratio:

Clenbuterol increases lean muscle mass but not endurance in patients with chronic heart failure.

J Heart Lung Transplant. 2008 Apr;27(4):457-61.
Kamalakkannan G, Petrilli CM, George I, LaManca J, McLaughlin BT, Shane E, Mancini DM, Maybaum S.
Division of Cardiology, Department of Medicine, Montefiore Medical Center, Albert Einstein College of Medicine, Bronx, New York, USA.


Clenbuterol, a beta(2)-agonist with potent anabolic properties, has been shown to improve skeletal muscle function in healthy subjects, and in high doses, promotes cardiac recovery in patients with left ventricular assist devices. In a small, randomized controlled study, we investigated the effect of clenbuterol on skeletal muscle function, cardiac function, and exercise capacity in patients with chronic heart failure. Clenbuterol was well tolerated and led to a significant increase in both lean mass and the lean/fat ratio. Maximal strength increased significantly with both clenbuterol (27%) and placebo (14%); however, endurance and exercise duration decreased after clenbuterol. Prior data support combining exercise training with clenbuterol to maximize performance, and on-going studies will evaluate this approach.

Anyway, the point here is that human data is beginning to filter in, albeit in a rehab/post-operative scenario, showing that Clenbuterol does in fact have an anabolic effect in humans.