There've been quite a few developments in psychiatry I'd regard as legitimately scientific (the discovery of lithium as treatment for manic-depressive illness would be an obvious example)...

Is it? Because, while it's certainly an effective treatment for some varieties of bipolar disorder, we still have no idea why it works. One can't help but think of medieval doctors ascribing the success of their poultices and herbal remedies to a change in the balance of the body's humours -- even if it does actually work, it's still primitive science.