If they were a placebo, then any remedy would work. But sometimes they don't until you hit the right one. Also, they have proven results on animals, plants and children.
That's not to say that the simple power of suggestion wouldnt have any effect. There are some people who are of the belief that they can receive the effects of a remedy simply by placing the appropriate one in front of a monitor and allowing it to transmit over the internet. I've not researched this myself, but my feelings tell me it's probably more power of suggestion that they can take them that way more than anything else.
Another clear indication that they work well is that the Rescue Cream heals burns better than anything I've seen. That cannot be just due to the power of suggestion.