Tribulus is natural, but by itself its doesnt do much.I would stack it with DHEA, which I beleive is still natural.Then try to find some Longfolia, but make sure its a 200 to 1, or atleast a 100 to 1 ratio, this way its really strong.Other good herbs for increasing testosterone is MACA, Muira Puama, Horny Goat Weed, Velvet Deer Antler and Even Yohimbe.There all work well, you could even stack them together.
Are they are strong as steroids hell no, but atleast you will still be natural, but you will increase your natural testosterone levels.The stack below will be considered natural but would riase your test level very significantly
DHEA 200mg
Tribulus 1000mg
Longfolia 1000mg
Yohimbe Hcl 10-15mg