There is more doping in athletics now because the potential prize money available is "bigger than ever", according to a former US sprinter who was himself banned from the sport in 2005.
Tim Montgomery was speaking after a decision today to ban the Jamaican sprinter Asafa Powell for 18 months after he tested positive for the stimulant oxilofrine.
Montgomery said he could not see why an athlete would "go into a competition not knowing what they're taking".
Jamaican sprinter Asafa Powell has issued a statement calling his 18-month ban for taking a banned substance 'patently unjust'.
Powell, 31, said he had unknowingly taken oxilofrine when he was using a legal supplement called Epiphany D1.
He added that his team had contacted doping authorities to point out that oxilofrine was not listed as an ingredient for Epiphany D1.
The former world record holder also questioned the severity of his punishment, claiming it was "clearly not based on the offense nor the facts surrounding it".
Powell's team is now preparing to take his case to the Court of Arbitration for Sport in Switzerland.
Former 100 metres world record holder Asafa Powell has been banned from athletics for 18 months for doping.
The 31-year-old Jamaican sprinter has competed at the last three Olympics and broke the world record in 2007 when he ran the 100 metres in 9.74 seconds at an event in Italy.
Powell tested positive for a banned substance in July of last year.
Sir Roger Bannister said one of Sir Christopher Chataway's finest moments was when he smashed the 5,000m world record in 1954.Read the full story ›
David Cameron has paid tribute to record-breaking athlete and former Tory politician Sir Christopher Chataway, saying "we have lost a great Briton".
Sir Christopher Chataway, who died today aged 82, was the first winner of BBC's Sports Personality of the Year award after setting the 5,000m world record at 13:51:06.
He retired from professional athletics after the 1956 Olympics but kept on running for decades afterwards and completed the Great North Run a few years before his death.
Sir Christopher Chataway was an all-round man.
Besides his 5,000 metres world record and his role in helping Sir Roger Bannister become the first man to break the four-minute mile barrier, Sir Christopher was also the face of the very first ITN newscast in 1955.
Sir Christopher, who died today aged 82, was the first ever winner of BBC Sports Personality of the Year, after setting the 5,000m world record at 13:51:06.
Although he retired from professional athletics after the 1956 Olympics in Stockholm, he continued to compete until recently.
In 2006, aged 75, he completed the Great Northern Run half marathon 1:38:50
Sir Christopher Chataway, who died today aged 82, said running "returned to be a friendly codger" in his old age after acting as a tormentor in his younger days.
Speaking about taking part in the Great North Run at almost 80-years-old, Sir Christopher said at the time: "I sometimes think that running, which was a sort of tormentor in my youth, has returned to be a friendly codger in my old age - that what was Joe Stalin has turned into Dixon of Dock Green."
He is survived by his sons Mark, Matthew, Adam, Charles, Ben, his daughter Joanna, his wife Carola and his former wife Anna.
The son of athlete Sir Christopher Chataway, who died today aged 82, said his father continued running late in life and clocked up a "very respectable" time in the Great North Run three years ago.
He kept running almost until the end of his life. He ran with a couple of my brothers in the Great North Run about three years ago now.
And then doing it in a very respectable time.
Mr Chataway said he believed Sir Christopher would like to be remembered as "a wonderful father, a husband, a grandfather".
"Those probably mattered more than any of the sporting or political things," he said. Sir Christopher was also a Conservative politician and broadcaster.
A former 5,000 metres world record-holder who set the pace to help Sir Roger Bannister become the first man to break the four-minute mile barrier in 1954, has died aged 82.
Sir Christopher Chataway died at around 7am this morning at St John's Hospice in north west London having suffered from cancer for two and a half years, his son Mark Chataway said.
The athlete's interest in keeping fit stayed with him as his life progressed and his son said that up until a couple of weeks ago he was on the exercise bike every morning.
Mr Chataway, 53, described his father as a "very compassionate and wise man" who had the "ability to put other people's needs first".
"We were, especially in these last few years, struck by his amazing qualities of humility and strength," he said.