"We've spent the better part of the year shooting our next movie, SICKO. As we've done with our other films, we don't discuss them while we are making them," Moore wrote. "If people ask, we tell them SICKO is 'a comedy about the 45 million people with no health care in the richest country on Earth."

Moore also said that he received 19,000 responses to his February call for letters describing personal experiences with the health care system.

He added that the documentary is straying from that simple premise. "I don't think the country needs a movie that tells you that HMOs and the pharmaceutical companies suck. Everybody knows that. I'd like to show you some things you don't know. So stay tuned for where this movie has led me. I think you might enjoy it."