Bill Cosby -- Copped to Using Quaaludes and Sedatives on Women

Bill Cosby bought Quaaludes and used Benadryl to knock out at least one woman ... something he admitted during a deposition for the sexual assault lawsuit a Temple University employee filed against him.

Cosby gave the shocking testimony in 2005. He eventually settled the case with Andrea Constand for an undisclosed amount of money ... but documents connected to the case were just released today.

During the depo ... Cosby said he had purchased the 'ludes with the intent to give them to women he wanted to have sex with. He also said he had given Constand 3 half-pills of Benadryl.

The AP filed docs asking a court to release the testimony, and Cosby's attorneys tried to have it blocked ... claiming revealing the material would embarrass him.

Of course, Cosby has since been accused of sexual assault by dozens of other women. He has never been criminally charged.