County coroner Dr. Carl Parrott said the drugs are stimulants sometimes linked to "bizarre and violently aggressive behavior."
A civilian watchdog panel born from riots that followed the shooting of an unarmed black man in 2001 is looking into the matter.
Nathaniel Jones, 41, died at a hospital shortly after being taken into custody Sunday. The 350-pound man was struck repeatedly with nightsticks in a confrontation captured by police cruiser video camera.
The preliminary autopsy also showed he had an enlarged heart.
Local NAACP president Calvert Smith says the findings help explain why Jones acted the way he did, but "I'm not sure, however, it changes the frustration and the disappointment that we experience because another African American man has died as a result of an encounter with the police," he said on CBS News' The Early Show.
The bruises found by medical examiners on Jones' calf, thigh and buttocks of Jones' right side, presumably caused by the repeated blows from the officers' batons, show no evidence of causing damage to Jones' internal organs, the preliminary report said.
Within hours of this weekend's incident, police produced photographs of the officers' injuries, reports CBS News Correspondent Byron Pitts, and according to experts, the officers appear to have used a proper amount of force.
"I don't get a sense this is a Rodney King-style beating," said Eugene O'Donnell of the John Jay College of Criminal Justice in New York.
"We caught an arrest and a violent struggle on video and don't think that's ever going to look good," he said, "but I think it's pretty clear that the police didn't act over the top in this case."
"This is the continuation of what has been a series of incidents like this over a number of years and because of that, it gives rise to the concern that we express about this incident," said Smith.
The NAACP will conduct its own investigation into the death.
"If you look at the whole tape, what you see is the officer telling (Jones) to stay back," said Cecil Thomas, a former city police officer and director of the Cincinnati Human Relations Commission. "But then the individual clearly attacked the officer."
Activists charge police used undue force against an unarmed man. Not so, says Police Chief Thomas Streicher.
"Police officers are wearing a gun belt, they do have a gun on, and once you go down on the ground, everybody has equal access to that firearm, so it is considered an armed encounter at that point," he said on The Early Show. "The officers are well within their rights to defend themselves and to use force to overcome resistance to arrest at that point."
The Citizen Complaint Authority, created after the 2001 riots, was already looking into the death, with investigators going to the parking lot of a fast food restaurant where the beating took place hours later, panel chairwoman Nancy Minson said.
She said the complaint board began its investigation on its own, which it can do when a death involves police or when shots are fired.
"We turn to you for a full and fair and thorough investigation," Mayor Charlie Luken told members Monday night.
Monday night's regular meeting of the panel was disrupted by four activists who demanded quick action.
"It's apparent that you don't know what you're supposed to be doing and what your authority is," said Nate Livingston Jr., a member of the Coalition for a Just Cincinnati, which promotes a boycott of the city.
"When they start fighting in the streets, you'll say, 'Why didn't you do it the right way? Why didn't you come to City Hall? Why didn't you trust us? Why didn't you talk to us?'"
Minson called police to escort Livingston and three others from the room when they continued to shout at the panel.
Jones' death raised new allegations of police brutality, just as the city was starting to recover from the effects of the April 2001 riots and the boycott that followed.
Justice Department spokesman Jorge Martinez said information was being gathered to determine if federal action was warranted.
Fire emergency personnel responded early Sunday to a report of a man passed out on the grass outside a fast-food restaurant, then called for assistance because the man was becoming a "nuisance."
All six officers who responded — five whites and one black — were placed on administrative leave, which is standard procedure.
The 2001 riots stemmed from the shooting of Timothy Thomas, 19, who was wanted on several misdemeanor charges and fled from police when they tried to arrest him. Officer Stephen Roach shot him in a dark alley and was later cleared at trial of criminal charges.
A federal investigation of the shooting, requested by the city, resulted in an agreement to tighten policies on use of force and improve handling of citizen complaints.
In February, a white officer chased and fatally shot a black man who was seen running from a store that had been broken into. Police, prosecutors and the Citizen Complaint Authority concluded the shooting was justified because the suspect was beating the officer with his nightstick.