I began using Sierra Sil personally to see if it would help. Before using Sierra Sil I was unable to run for more than fifty yards. After using Sierra Sil for about two months I was able to run as far as my 60-year-old heart would take me (about 5K)! I began recommending Sierra Sil to my patients and the results have been impressive. There are very few people who either cannot take Sierra Sil or do not notice any benefit, but the vast majority find it very helpful. The demand has become so great I have trouble keeping it in stock. I recommend it without reservation.