The adaquan helps the joints by restoring liquid "lubrication" to them. It is usually prescribed like "one shot per week for 4-8 weeks". Normally, a pain reliever is also prescribed to help with the pain. Think of it as if you took chondroiten (sure I spelled that wrong) to help with arthritis pain or to prevent arthritis, but also needed a steroid or NSAID to help with pain flare-ups. Adaquan will help with the pain, eventually, because it will make the arthritis lessen or go away. The other pain relief is to take the pain away until that time.
Vets can also prescribe steroids, NSAIDS, or pain meds like Bupe that will relieve the pain while the adaquan helps fix the problem. If he's limping due to the administration of the shot itself, a pain med can take away that pain too.
Is your cat dehydrated at all? Sometimes just sub-q fluids can help. Are the shots sub-q or IM? Aduquan is also used on dogs and horses, and in some cases with horses (according to what I read last night) they inject it directly into the joint in bad cases.