Animal Pak helped me to add weight; I felt more solid while taking Animal Pak, like I could handle more and do it safely. But I stopped using it because I found something better.
The Dr Max Powers Anabolic Stack was recommended to me several years ago by some random guy in my gym. It has helped me to put on and keep on some good muscle in several ways. First, if I take it before exercise, I feel like I can keep pushing and pushing and always have more left in the tank. Lifting heavy for an hour and a half was no problem, though I try to keep my workouts shorter.
There are a lot of pills, and that definitely takes some getting used to. Totally worth it.