My puppy (he is 7 months old) was on a beef and rice diet for a while. I decided that he probably could use some vitamins, so I started giving him these vitamins once a day. The day after I started him on the vitamins, he became constipated and did not have a bowel movement until the day after I stopped feeding him the vitamins. He was on the vitamins for a week - that's a long time for a dog to not go! The plus side is that they are easy to find and cheap, so if your dog does not have a sensitive digestive system, maybe the vitamins won't have this affect on him/her.