I agree completly with this Merc, it is well documented and I've experienced it myself. The scientific literature has identified it as having a specific affect on post-excercise serum cortisol levels, thus it will be most effective when take immediately before or after your workout.
Mass quantities of Vitamin A. I tried it myself and I'm convinced it made a small difference. I was cutting and wanted to keep my strength. Despite being on a calorie-restricted diet and great deal of excercise, I lost no muscle mass or strength. I am skeptical, however, of its ability to substantially affect muscle growth on bulking cycles. It certainly is no substitute for good gear. That said, Large quantities of Vitamin A do indeed reduce cortisol levels. In fact, it is being researched as a treatment for Cushing's syndrome. (Cushing's patients have extremely high cortisol )
The abstract from one such study can be found here:
http://www.nature.com/nature/journal.../228762a0.html
There is much more literature out there but I've read most of it and I'm sure you are just as capable of googling as am I.
Good Luck!