Hundreds of tablets have been found mixed with food in an area popular with dog walkers where dog food was previously found laced with anti-freeze.
It is suspected the pills, believed to be anti-depressants, were deliberately dumped at Comber Greenway in Dundonald so they would be eaten by animals.
Even if they were dropped accidentally, they would be harmful to any children or pets who may come across them and end up eating them.
The drugs were found by dog walker Chloe Scammell.
She told UTV they were mixed with food intended to entice dogs.
Local vet James Buick has dealt with previous cases of dogs eating poisonous substances.
He advised dog owners who fear their pets may have eaten something they shouldn't to, where possible, bring a sample of what they ingested.
"Even if it's a few tablets, we can get a lot of information from that because treatment will be a lot different depending on what the animal has eaten," he said.
"If you've any suspicion at all, better to be safe than sorry."
No pets were reported ill as a result of eating any unidentified substance at this time, but police were called to the area and have taken the pills away for examination.