Scientific studies: Clenbuterol is used also to gain muscle mass. And burn fat.

Clenbuterol, fed for 1 wk, increased the wet weight of the gastrocnemius, soleus, and extensor digitorum longus muscles (15-23%) in both normal and D + I rats. Although clenbuterol increased body weight gain, it did not alter feed consumption and, therefore, feed efficiency (g gain/g food) was improved. Activities of cathepsin B and N-acetyl-beta-glucosaminidase, but not cathepsin D, were elevated in the soleus muscles of clenbuterol-treated rats. The clenbuterol-induced increase in muscle growth in the insulin-replaced diabetic rats indicated that this beta-adrenergic agonist effect was not mediated by an alteration of circulating levels of insulin, secondary to beta-agonist action on pancreatic insulin release. https://www.ncbi.nlm.nih.gov/pubmed/3310657 Clenbuterol treatment increased the weight of skeletal muscles 22% to 39% in 3-month-old rats, 19% to 35% in 12-month-old rats, and 22% to 25% in 23-month-old animals. Likewise, clenbuterol increased carcass protein content 19% in 3-month-old rats, 16% in 12-month-old rats, and 24% in 23-month-old animals. Conversely, the drug reduced carcass fat content 36% in 3-month-old rats, 32% in 12-month-old rats, and 38% in 23-month-old rats. Therefore, clenbuterol had similar anabolic and catabolic effects in all age groups. In addition, clenbuterol stimulated recovery of skeletal muscle protein lost following pump implantation in senescent rats. https://www.ncbi.nlm.nih.gov/pubmed/1861634 Clenbuterol is not only used to burn fat, it's used to generate muscle mass as well. It has both effects.