Embattled US comedian Bill Cosby admitted having drugged at least one woman with a sedative to have sex with her, court documents show.

Cosby, accused of sexual assault by some 30 women over decades but who has so far escaped justice, made the admission in a deposition in 2005, talking about an incident from 1976.

The 77-year-old was questioned by Dolores Troiani, a lawyer for Andrea Constand, a former women's basketball director at Philadelphia's Temple University where Cosby studied and was a member of the board of trustees.

Constand took her rape case to court, but the case was dropped.

Cosby's lawyers had long sought to block publication of the court transcripts, but they were released Monday on the PACER public court records website.

In one exchange between Cosby and Troiani, the comic admitted having obtained seven prescriptions for Quaaludes, a powerful sedative drug.

"You gave them to other people?" asked the attorney.

"Yes," replied Cosby.

Troiani then asked him: "When you got the Quaaludes, was it in your mind that you were going to use these Quaaludes for young women that you wanted to have sex with?"

"Yes," replied Cosby, although a short time later he said he had misunderstood the question, and was referring only to one woman.

"I misunderstood. Woman, meaning T....., and not women," he said.

Later in the deposition, Cosby said: "I meet Ms (T, whose name was redacted to preserve her anonymity) in Las Vegas. She meets me back stage. I give her Quaaludes. We then have sex."

The entertainer resigned from the board of Temple University last December, as sexual abuse accusations against him multiplied.

Cosby is famous for his role in "The Cosby Show," a popular family sitcom that aired in the 1980s and 1990s.