Q. What is a safe effective joint pain treatment for a 13 Amstaf?
A. Joint supplements can make a world of difference when it comes to joint ailments and in my experience, their benefits have out weighed any side effects which are usually minimal. If your dog does have a reaction to these, its generally gastrointestinal upset (unless they have an allergy) which can be further reduced by decreasing the dose, or giving it with food, and in the beginning slowly weaning them on and up to the recommended dosages.
You can also discuss with your vet different injections available for joints. I have seen quite a lot of success with some of these as well, depending on the problem.
These all can help with mobility and some of the pain. If you are looking for a specific pain med, you will need a consultation with your vet as there are other health factors of your dog that been to be considered.