He took advantage of 22 women aged between 18 and 37 after meeting them through a Facebook application.
Azuar Ahamad, 42, raped, sexually assaulted or molested them, and also stole from some of them.
He faced 33 charges, including rape, sexual assault, theft, possession of obscene films and voluntarily causing hurt to his victims by giving them stupefying drugs, and he pleaded guilty on Monday to raping three women and sexually assaulting a fourth. The remaining charges will be considered during sentencing.
In 2009, police officers found in his mobile phones videos of him having sex with unconscious women. The prosecution says that he drugged them with sedatives, but he disputes this.