My Doberman, Skeeter Bug, had an elevated ALT liver enzyme that was astronomical (1550, with the norm being around 118, depending on which lab you use). I began using Herbsmith's Milk Thistle product two days after receiving the blood test results. Two weeks later, her ALT was down to 444, and two weeks after that, down to 135. We do not know what caused the initial elevation, and the only thing I changed in her life was the addition of the Milk Thistle. I must conclude (with my vet's blessing) that the Milk Thistle is a lifesaver. I have learned that I can keep her on this product indefinitely, and will do so. I thoroughly and highly recommend this product if your canine is have liver issues. Thanks again for the help regarding how long I can use the Milk Thistle. My heart rests in knowing I am doing the best I can for my Bug!!