What happens if you take double dose of testosterone boosters? I am just curious, would it increase your testosterone levels even higher, or will it damage your body?

Both are possible! Too much of a good thing is wonderful! (Mae West) In this case it is the opposite!
Waste twice ur money. Over-the-counter testosterone boosters don't work. There's no credible proof of effectiveness nor safety of any of these products or other dietary supplements for that matter. Check out 2 recent news articles: http://goo.Gl/bbmdcw (usa today) & http://goo.Gl/uilodl (fda via nbc) re lack of oversight & contamination.
Not recommended. I don't know exactly what is testosterone booster? Commercials run ads about this since i don't know the composition of their contents, i can't pass a sensible jugdement. Is your t. Low? Have you checked it.