Powell says therapist injected him
Jamaica's Asafa Powell reacts after the men's 100m final at the athletics event during the London 2012 Olympic Games on August 5, 2012
The 31-year-old Jamaican sprint star said he received "four injections," including vitamin B12, from Christopher Xuereb, who Powell had been working with for two months.
"It took me four weeks to have confidence in him," Powell told the three-member panel.
The panel also asked if Xuereb was the first person outside of a doctor to give him injections.
"Yes, he was recognized," Powell said of Xuereb. I got the same injection once by Dr Hans-Wilhelm Muller-Wohlfahrt."
The German physician is known for working with Bayern Munich of the German football league and sprinter Usain Bolt.
Powell also testified that he doubled the dosage of his supplements the morning of his positive drug test.
The sprinter said he did so on the advice of Xuereb.
Powell, who tested positive for the banned stimulant Oxilofrine at the Jamaican national championships in June, said Xuereb told him to take two capsules of Epiphany D1 each morning for the first week, then double it for the second week.
Powell claims Epiphany D1 was the source of the Oxilofrine.
"I didn't remember to do that (double the dosage). Chris (Xuereb) came to my room the morning of the trials and said I must remember to take four," Powell said.
The hearing in front of a three-member panel is scheduled to last two days.
Powell said he started taking the supplements from Xuereb, a Canadian physical therapist, about a month before the Jamaican championships, which were held June 20-23.
Powell also testified that he couldn't remember the names of the supplements he was taking at the time and he had not checked to see if Epiphany D1 was on the World Anti-Doping Agency's list of banned products.
"I don't know the list, but I knew of the list," Powell said. "I know there is a list we are supposed to check."
Powell also said he did not include Epiphany D1 on his doping control form.
"I could not remember after all the excitement at trials," he explained.
"All the supplements were new to me, so I could not remember all of them."
Powell's training partner Sherone Simpson, a three-time Olympic medallist, also tested positive for the same stimulant. Both sprinters have been banned from competing.
Simpson told the panel that she knew Powell was taking the same supplements as her.
Powell, one of Jamaica's greatest sprinters of all time, set a world record in the 100 metres in 2008 with a time of 9.74 seconds.