Kava can be potent, but I have found that most pills/tablets/capsules that you buy of Kava at the local pharmacy or health food store will be rather weak. You'd need to take quite a few of them to really feel the effects. However if you can get fresh kava, or whole leaf/root in bulk from somewhere and make your own extract/tincture then it can be far more potent.
I have found valerian from the local pharmacy/health store to be more potent than any kava I have ever purchased form the same type of shop, but, likewise, I would normally need to take 1000mg+ to feel any effects.
[that being said, my GABA_A receptors seem to be generally more unresponsive than most folks']