The 24-year-old said he kept drinking the iced tea as he needed a thirst-quenching drink at work.
He eventually opened up the cup to find three bags of cannabis, which had become punctured when he was poking around with his straw.
"Well, I was high and panicking and at work, so I called my dad,” Brown said.
“I didn’t want to get in trouble for this.”
Brown said the rest of his meal, which included 10 chicken nuggets and a double cheeseburger, was completely normal.
He claims the McDonald's worker paused as he ordered the iced tea, saying back "extra lemon?" in an odd voice.
Once Brown realised he was drug-affected, he called his dad, who told him to call the police, and it was “a whole ordeal.”
“And then, it gets worse,” Brown said.
“I called dispatch and the woman yelled like 'What!? Call 911!'. And I was like, ma'am, you are 911. She couldn’t believe it.”
Brown said he had a hard time convincing his manager and authorities what happened.
A police officer took one sniff of the drink and knew what it was.
“The officer asked me why I drank it and I was like, ‘Well, I was thirsty!’” Brown said.
Brown said he paid the regular price for the items. Police are investigating the incident.
7NEWS.com.au has contacted McDonald's for comment.
This story originally appeared on 7NEWS.com.au.