Garrett Bishop, owner of the doggy daycare, said the tossed object was actually several baggies of heroin, at least one of which was eaten by a dog named Charlie before employees could get to it.
"All in all, 17 baggies were found in our playroom, not including the five that the guy tried to swallow," Bishop told KMGH-TV.
Employees quickly notified Charlie's owner, Laura, who asked to be identified only by her first name.
"You can't process the fact that your dog ate heroin," Laura said.
She said she was at work when she received the phone call.
"She's high on heroin," Laura recalled being told about Charlie. "We're treating her but you need to come as soon as you can."
The daycare took Charlie to a veterinarian, who created the canine with charcoal and heroin antidote Narcan.
The Denver Police Department said its Victim Assistance Unit is looking into reimbursing Laura for her vet bill, which totaled more than $500.
Police said the suspect was taken into custody and is likely to face drug charges.
Laura said Charlie is on the mend, but has a ways to go.
"She still has no energy," she said.
Dogs and drugs are well known to be a bad combination -- a Chihuahua named Jack Sparrow underwent emergency treatment in California and was seized from his owner earlier this year when he tested positive for meth.
