01/30/2014 01:31 EST | Updated 04/01/2014 05:59 EDT

Toxicology report says Justin Bieber had marijuana, Xanax in system after Fla. arrest

MIAMI - A preliminary toxicology report shows that Justin Bieber tested positive for marijuana and the anti-anxiety drug Xanax after his arrest last week in South Florida.

The report released Thursday by the Miami-Dade County State Attorney's office also shows no presence of other illicit drugs in Bieber's system, such as cocaine or oxycodone. The 19-year-old pop star was arrested last week on Miami Beach on charges of DUI, resisting arrest and having an expired driver's license.

Bieber has pleaded not guilty but told police after his arrest last week that he had been smoking marijuana and took a prescription drug.

A previous Miami Beach Police Department report found that breath tests placed Bieber's blood-alcohol content below the .02 level considered intoxicated for under-21 drivers.

Bieber and R&B singer Khalil Amir Sharieff were arrested police described as an illegal street drag race between a Lamborghini and a Ferrari. Sharieff is also charged with DUI.

Bieber, a Canadian native, turned himself in Wednesday to police in Toronto on a charge of assault for allegedly hitting a limousine driver several times in the back of the head last month.

The singer remains under investigation for felony vandalism in Los Angeles County over an egg-tossing episode that damaged his neighbour's home. Detectives searched his home on Jan. 14, and prosecutors have sought additional information before determining whether to pursue charges.