Leucine is one of the building blocks of protein, particularly from animal foods, and it can be consumed through meat, dairy, soy, beans and other protein-rich sources. It's also widely sold as a dietary supplement. You can purchase a combination of leucine, isoleucine and valine branched chain amino acids by visiting BCAA supplement. BCAA also has glutamine amino acid. If you wish to increase muscle mass, consider creatine powder supplements or Creatine-capsules.

L Leucine and Muscle Tissue
Leucine or L leucine is an essential amino acid, which means the body cannot manufacture it and it must be ingested through dietary protein. Along with other essential amino acids, leucine helps maintain muscle mass -- which has made leucine-containing supplements a favorite of bodybuilders and athletes. But, what do studies say? A human study shows no benefit while an animal study show leucine supplementation prevents muscle loss.

Long-term leucine supplementation does not increase muscle mass or strength in healthy elderly men.
Am J Clin Nutr, 2009. From the Department of Human Movement Sciences, Nutrition and Toxicology Research Institute, Maastricht, Maastricht University, Maastricht, Netherlands; the Department of Clinical Chemistry, Maastricht University Medical Center, Maastricht, Netherlands; and the Rehabilitation and Health Centre, Virga Jesse Hospital, Hasselt, Belgium. Leucine was provided by Ajinomoto Co, Inc.
It has been reported that the blunted muscle protein synthetic response to food intake in the elderly can be normalized by increasing the leucine content of a meal. The objective was to assess the effect of 3 months of leucine supplementation on muscle mass and strength in healthy elderly men. Thirty healthy elderly men with a mean age of 71 y were randomly assigned to either a placebo-supplemented or leucine-supplemented group. Leucine or placebo (2.5 g) was administered with each main meal during a 3-mo intervention period. Whole-body insulin sensitivity, muscle strength (one-repetition maximum), muscle mass (measured by computed tomography and dual-energy X-ray absorptiometry), myosin heavy chain isoform distribution, and plasma amino acid and lipid profiles were assessed before, during, and/or after the intervention period.: No changes in skeletal muscle mass or strength were observed over time in either the leucine- or placebo-supplemented group. No improvements in indexes of whole-body insulin sensitivity (oral glucose insulin sensitivity index and the homeostasis model assessment of insulin resistance), blood glycated hemoglobin content, or the plasma lipid profile were observed. Long-term leucine supplementation (7.5 g/d) does not augment skeletal muscle mass or strength and does not improve glycemic control or the blood lipid profile in healthy elderly men.

A diet rich in the amino acid leucine might help prevent the muscle loss that typically comes with aging. French researchers found that a leucine supplemented diet restored a more youthful pattern of muscle-protein breakdown and synthesis to elderly rats. The older animals had shown a tendency toward excessive protein breakdown before going on the leucine rich diet, but the amino acid appeared to erase that imbalance. It's well known that after the age of 40 or so, people gradually lose muscle mass, and it's thought that an imbalance in muscle-protein synthesis and breakdown is involved. In younger people, this process is typically in balance. For example, research shows that after a meal, muscle-protein breakdown slows, whereas synthesis ramps up in response to the influx of amino acids from food. But in the new study, older rats did not show this post-meal dip in protein breakdown, whereas their younger counterparts did. A short time on the leucine supplemented diet, however, restored a youthful pattern of protein breakdown in the elder rats. December, 2005 issue of the Journal of Physiology.

Questions
Q. Does a leucine supplement help with muscle mass as good as creatine does?
     A. I doubt if a l leucine supplement is as effective as creatine. Creatine is one of the most important supplements for muscle growth that I know of and would far surpass the effectiveness of leucine supplement.

Q. My friend gave me a bottle of leucine powder. What would this be used for?
     A. I don't really know why anyone would need to take a leucine powder supplement since I think all the amino acids are helpful for health and I don't see the need to take a leucine supplement by itself. However, having said this, I realize that there has been a study that a leucine supplement given to older rats was helpful for muscle tissue. But I think creatine or a general protein supplement would be preferable.