so many things.... "science" actually doesn't need quotes. I must cop to using unnecessary quotes a lot myself, so I suppose I'm on shaky ground here. But yeah, science is good at eventually dismissing useless medical treatments. To be more accurate, it's good at identifying which ones work and the mechanisms behind them. So technically you certainly can say accupuncture "works" (i told you I like unnecessary quotes). But it works solely by the placebo effect. It's been well studied, I bet Google has lots o great stuff about it. Medical journals do too, and blogs by researchers - and some of them are easily found using Google. Maybe you did find some research reports that were convincing in support of accupuncture. My simple Google search didn't find any that fit that. Sure there are some authors with MD or PhD after their names who claim there's scientific evidence. I didn't find the content of their arguments (I like italics too) matched the implied expertise of their credentials. For example, one started his argument by pointing out that western medicine doesn't understand chi, so it can't measure what accupuncture's doing. Sadly, that just leads to the need to explain why chi exists and has effects but can't be measured by science - accupuncture becomes a lesser component of a broader (undefended!) claim about a powerful but unmeasurable life force.
Typical skeptical disclaimer: I don't say that I know for sure chi doesn't exist, or that accupuncture doesn't work. I do know that neither has been proven, that other explanations for the effects some attribute to chi/accupuncture do exist and are sufficient. So if real evidence ever does show up, well then, my current skepticism is still justified, but I'll accept the evidence as it is. I don't have a horse in this race, chi's a cool idea, but it seems an arbitrary construct to me. I don't see the difference between it and the Force emitted by the midichlorians (or however George Lucas spells them). Dismissing one because it was invented more recently than the other seems unfair.
Your observation that "scientific studies on human health" are difficult (quotes correct here!) is absolutely true, it's why there's been years of research regarding some of the alternative medicine world's claims - especially regarding accupuncture, which has good anecdotal evidence in its support - even though there's been little success finding an effect that can't be otherwise explained. It's important to be careful and critical about accepting poorly supported results. To belabor a point: the scientific method can be used to test the efficacy of treatments such as accupuncture. There does not exist a body of successful experiments that demonstrate a clear effect, or show a mechanism by which it works. There are several studies that fail to disprove any effect. I suppose that's something. As you say, it's difficult to isolate one factor when we're talking about health studies, but there don't seem to be any that are strongly indicative in accupuncture's favor, and there doesn't seem to be a large number that are slightly indicative either. So it can be regarded at best as an unproven treatment. For a treatment that has been around for so long, to have the best evidence in its support being anecdotal or even weirder being that it's been around a long time, so there must be something to it, should lead one to be skeptical at best.