Toronto's Hospital for Sick Children is dealing with more fallout from a drug research controversy that erupted last year.

A prominent researcher, Dr. Gideon Koren, was temporarily suspended Tuesday after he admitted to sending intimidating and anonymous letters to doctors who supported Dr. Nancy Olivieri.

Koren and Olivieri worked together for years testing an experimental drug for the pharmaceutical company Apotex.

But a split developed between the two researchers. Olivieri believed the drug wasn't safe and went public with her concerns.

She accused the hospital of not supporting her when Apotex threatened to sue.

Koren, on the other hand, believed the drug was effective.

Hospital president Michael Strofolino says what started as a scientific collaboration that evolved into a disagreement obviously evolved into personal issues.

Koren's suspension came after the results of an investigation into the poison pen letters was released Monday.

The letters were sent to doctors from October 1998 to May 1999 at the height of the battle between the hospital and Olivieri.

Dr. Peter Durie, a colleague of Olivieri and a senior scientist, received four of them.

"We believe that any normal-functioning hospital would have let people like you go long ago," one of the letters said.

Other letters included profanity and one referred to Olivieri and her supporters as pigs.

Koren faces a hearing in early January that could result in his dismissal.