Of course there is no scientific proof , there never will be any on bodybuilders or gym rats , but stacking compounds for physical enhancement does have a synergistic effect , asking if its additive is just playing with words as its the same thing , you should be a politician Van 
yeah i agree completely, in this sport of ours, with the drugs we use, most "evidence" is either speculatory or circumstantial.......... we are the ginny pigs........but it is pretty much proven that stacking compounds is more benificial then just taking more of one singular compound.
and as far as whether the effects are "additive" or "synergistic"..............that's just mincing words.
Nah, it's not just playing with words. It's not the same.
Example, which is better for growth:
1000mg test
or
600mg test + 400mg Deca
You'll get both types of opinions from different users. Some will say test alone is best and vice versa.
Stacking steroids definitely is additive... when your total dose is greater! More androgen, more growth... up to a point.
Stacking might even be the opposite of synergistic sometimes and hurt gains as steroids can "compete" with each other. I saw where Phil Hernon said if he could go back in time he wouldn't use Deca as he feels it hurt his gains from testosterone.
Now I'm not saying there can't be synergistic effects, there probably are in some cases, just that it's experimental and all bodybuilders don't feel the same way about different stacks.
I'm sure you'll both agree that you've heard bodybuilders say, "man, I get just as good gains with just test, I don't need to add a second drug".
