A report by Pieter Cohen, a Boston physician and Harvard faculty member, reviewed two case studies in Massachusetts that illustrate the major problems with the pills and their unreported components, The Boston Herald reported. Use of the diet pills was first reported to be widespread in South Florida in 2005.

In an interview with the Herald, Cohen said the pills are being used "by a very large number of people in our community and I suspect in your community." He said the pills, which in South Florida often list ''all-natural ingredients,'' are used by Brazilian immigrants in Massachusetts.

His research revealed that the diet pills are "extremely common" in Brazil, with doctors there writing "maybe hundreds of thousands of prescriptions a year."

The pills are brought into the United States by either Brazilian immigrants or by illegal importers who peddle the pills by word of mouth, Cohen said.

The pills are not approved for sale in the United States. In 2006, the Food and Drug Administration warned that some types of the pills contain controlled substances and "could lead to serious side effects or injury."