The date-rape drug gamma hydroxybutyrate (GHB) is both colourless and odourless. (CBC)

Kelowna RCMP are trying to determine whether a date-rape drug had anything to do with an unusual incident in a park Monday morning.

A 30-year-old woman was found partially clad in the city's Mission Creek Park by a passerby.

The woman, who cannot be identified, was unable to tell police how she got to the park or why she was wearing only her underwear.

The last thing she remembered was being at a pub near the park.

The initial investigation did not turn up any signs of sexual abuse, but police said the incident did have the earmarks of a sexual assault.

Const. Steve Holmes of the Kelowna RCMP said police are investigating the possibility the woman's drink was spiked.

"That is an avenue we are looking at. However, it is difficult to determine," he said. "The two most popular date rape drugs that are out there are very short acting in the body. An analysis has to be done fairly [expeditiously] to find [a] trace of anything."

The woman's camera bag, cellular phone and wallet were found nearby.

Mission Creek Park was closed for approximately four hours Monday afternoon and a police dog was brought in to search for evidence.

Holmes said police are taking the matter seriously.

"It is a very real concern. Drug-assisted sexual assaults do occur and unfortunately in the summertime they do spike with respect to the occurrences," he said.

The two most common date-rape drugs are Rohypnol (the brand name for flunitrazepam, a tranquilizer) and gamma hydroxybutyrate, commonly known as GHB.

Both drugs produce a feeling similar to that of being intoxicated. Side effects include sleepiness and a loss of memory.

The effects of both drugs can last up to eight hours.