There are people who claim abduction and experimentation by aliens, with some of the accounts going back years. Many of them have told the same stories under hypnosis, making it seem real enough. I do not doubt they were abducted by UFO's, but perhaps it was our own government, and not aliens, performing the experiments.
I don't believe there is any solid proof that aliens are visiting the world and capturing people to conduct experiments on them, until we can get some solid proof or photo evidence that such a thing does occur I think it's safe to say that it's highly unlikely to be occurring.
I do not think people get captured in UFO laboratories for experimentation. There is no solid evidence of extraterrestrial life ever being found on the planet earth, so for the most part the idea of people being abducted by UFOs for experimentation is most likely a hoax perpetrated for attention or revenue.
I honestly doubt people are captured by aliens for experiments. I do believe there is some secrecy regarding aliens visiting our planet and I suppose this could be kept a secret as well, but I think it would be much more difficult to cover these things up. I know some people have stories, but they always lack clear evidence.
I do not believe that people are getting captured by UFOs and being experimented on. I think most of the people who claim such things are usually mentally disturbed and untrustworthy. There is also no evidence to prove that such incidents have ever occurred in our history of mankind and the planet.