He has pleaded not guilty to all charges.
The Associated Press does not typically identify people who say they are sexual assault victims unless they grant permission, which Constand has done.
Some 60 women have come forward to say Cosby sexually violated them, all but destroying his nice-guy image, but the statute of limitations for prosecution had run out in almost every case.
Cosby, sitting across the room at the defense table, leaned in to listen, whispered to his lawyer and, at times, shook his head.
Constand is a former employee of Temple University, Cosby's alma mater.
"I was mistaken", said Constand, 44, now a massage therapist in Toronto. "I was obviously very distraught at. just the fact that he betrayed her".
"What was the one thing I asked you to do when I met you?"
On Tuesday, the defense asked her why she continued to see him after those reported attempts. "I really didn't see a problem in it at all [giving him my personal cell phone number]".
Constand lost consciousness after Cosby helped her to the couch and provided a pillow for support, she said.
Constand claimed on a later date she confronted Cosby to try to determine what pills he had provided to her. "I felt him reach for my zipper, and I leaned forward and stopped that". "I wasn't scared of someone making a pass at me".
Constand said she continued to be friendly with Cosby, until the alleged sexual assault in 2004.
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Smiling, dressed in a pale blue jacket and a white top, she answered initial questions from Assistant District Attorney Kristen Feden calmly but her demeanor changed when the testimony switched to the alleged assault.
"Put them down. They're your friends". Are they natural? Are they herbal?' He said, 'Yes. "They will take the edge off".
"He was a Temple friend, somebody I trusted".
"I'm not here for that", she recalled telling him. He said he could not read the prescription bottle, Gianna Constand testified, so he agreed to write it down and send it to her.
"You hadn't told the officers that previously you had gone to Mr. Cosby's home, and had wine and sat by a fire", Agrusa said. "It's really not my place to speak on that", she said. "When I stood up, my legs were not strong and I began to panic a bit", she added. "I was in no state of mind".
Frazier was accompanied by her husband John Atchison, a celebrity hairstylist whose clients include Cosby and his wife Camille. She testified she let Cosby know she wasn't interested in his advances. "I wasn't able to fight in any way".
About half an hour later, Constand said, she had trouble talking and difficulty moving and was suffering double vision. "I just wanted to go home".
NORRISTOWN, Pa. (AP) - The woman who accuses Bill Cosby of drugging and molesting more than a decade ago stood by her story at his sex-crimes trial Wednesday, withstanding hours of often tedious cross-examination that didn't produce the stumbles the TV star might have hoped for.
"No, ma'am, he never said a word to me", Constand said.
Constand left Philadelphia on March 31, 2004.
The deposition Cosby provided in that civil suit, in which he admitted to many of Constand's allegations, is central to the case against him.
Bill Cosby has arrived at a suburban Philadelphia courthouse for the third day of his sexual assault trial. Each charge carries a maximum sentence of 10 years in jail and a $25,000 fine.