The assaults occurred after the women left the Nickel Rose Lounge at 848 B St. on Sept. 11 and 21, police spokeswoman Margo Rohrbacher said.
The first victim, a 26-year-old woman, said she was drinking with friends at the Nickel Rose on Sept. 11 and left around 2 a.m. on Sept. 12, Rohrbacher said.
She woke up at home eight hours later and realized she had been sexually assaulted, Rohrbacher said. The woman told police she has no memory of anything between the time she left the bar and the time she woke up the next morning.
The second victim, a 22-year-old woman, was at the lounge with friends on Sept. 21 said she has no clear memories after about 11 p.m., Rohrbacher said. She was also sexually assaulted and woke up the next morning at a hotel in southern Marin County.
Police are investigating whether a substance was added to the victims' drinks without their knowledge. So-called "date rape" or predator drugs have sedative, hypnotic and an amnesic effect, Rohrbacher said.
"The term 'date rape' can be misleading because the suspect using the drug is not necessarily a date, but may be a complete stranger," Rohrbacher said. "Predator drugs can be used on men and woman and in both public and private settings."
The two women do not have friends in common, Rohrbacher said. The owner of Nickel Rose, Jennifer Ashby, has been helpful with the investigation, according to police.
"We are greatly saddened by this and we will do all that is in our power to prevent this ever happening again," Ashby said. "We are a woman-owned business with daughters of our own, we have and always will have zero tolerance for any inappropriate action toward women in our venue," she said.
Ashby said the nightspot is installing cameras immediately and will ensure that there is adequate security.
"We urge anyone who has any info whatsoever to go to the SRPD," Ashby said.
Police are reminding bar and nightclub patrons to take precautions, including not accepting a drink from a stranger, keeping their drinks with them at all times -- even when visiting a rest room -- and throwing away any drinks that have been left unattended.
"This is an unusual crime for us," Rohrbacher said.