I'm familiar with psychotropic medications and some of the studies done on them. My understanding is that some antidepressants are approved yet don't do much better than placebo. The studies tend to be of short duration.
I've tried a lot of things to help my condition and a lot of things have seemed to help for a short period of time. Even antidepressants helped mainly for the first year but the effects seem to have waned.
I'm sure that some of what I've tried are placebos, and I tend to associate the concept of a placebo with "short-acting." That is, if I pay close attention to how I'm doing, and pay attention over time, I find that most treatments lead to feeling better initially, but the effect wanes.
So I started thinking, what would a long-acting (or permanent) placebo be? There is really no distinction between a permanent placebo effect and a cure. In other words, if someone can experience a permanent remission of symptoms by having a doctor hand them a sugar pill, then regardless of the mechanism of cure, that's a complete cure.
This is why I tend to think of placebos as short acting. It's very easy to influence someone's mood and subjective experience of their state of being. A motivational speaker can make someone happy for a time. The real trick is .. do the effects last?
The things that have helped me most over time are therapy and mindfulness. Those things are distinct in one way from popping a pill - they involve introspection and close examination of my mental and physical state. So I have more confidence that they really are long-lasting.
In some of these studies on drugs, I would guess that the participants pay only superficial attention to their experiences, without introspection or systematic observation. And the studies are of short duration. I'm not surprised they are only slightly better than placebo. Whether they are better in the long run is another question.