Question about my dog?

My dog is 9, he won't play, and refuses to go on walks with me. I think it is because of his bones, or joints, because he does seem to have trouble getting up and walks very slowly compared to how he used to. What is the best joint medication you can think of, one that will make him want to play and go for walks? Also ones that do not have any bad side effects that could lead to other health issues. Thanks for any help.