Absence of evidence is not evidence of absence. But there is only an absence if you choose to throw out the hundreds of "not good enough" studies indicating effects in the same direction.

There is a weird contrarianism a lot of people seem to relish in when it comes to natural medicine having an effect.

The reason pharmaceuticals have studies that prove effects is because there is a giant profit engine powering them and a regulatory system requiring it. It's hard and expensive to do a huge well controlled study of garlic because most modern people eat garlic as a regular part of their diet. It would be hard to find statistically significant effects for prozac if the control group used it as a seasoning.