Like glittergoddess said, most of them just have oriental cinnamon in it.
I got duwop lip venom thinking it was going to make them pouty and stuff, and it didn't. Then I found out that the cinnamon is just meant to irritate the skin of your lips and especially around the outside edge of your lips, to make them look "bee stung" and give them the pinky color. Them (specifically lip venom, but I'm sure other ones too) saying it 'plumps' up the lips is more/less an exaggerated marketing tool...
**It still does not mean that it doesn't work on some people, because I know a few people who do get awesome results; I guess it's just most of the people don't, some people do...with that being said, I'd do research if I was going to get another lip plumper, just for the simple fact that they all run about $18 at the least, and regardless if it's $18 or $30 I'd want it to work...
mich.