Four-year-old Alex was eating his bowl of Coco Pops when he made a troubling discovery.

A NSW mum was left in shock over the weekend when she allegedly discovered a pill in her four-year-old son’s bowl of Coco Pops cereal.

Posting to Facebook, Karlee Tweedie shared a photo of the capsule her son discovered in his breakfast.

“Everyone with kids who eat Coco Pops please be careful,” the mother from Lake Macquarie wrote.

“Alex was eating cereal and at the end we found a capsule in it,” she added.

Speaking to Nine News, Karlee explained how she discovered the pill in her child’s food.

“My son had eaten his cereal and when he was at the bottom of the bowl he came in to me and goes, ‘Mum look’,” she said.

“I looked in his bowl and there the capsule was. It was still together and when I lifted it out, it mashed up.”

The pill Karlee reportedly found in her son's cereal. Image: Facebook.

It's believed the pill discovered in the bowl of cereal is Duromine, which is a drug often prescribed to assist weight loss in obese patients.

According to Health Direct, side effects of using the pill can include vomiting, nausea, stomach cramps and headaches.

"I'm freaking out for my son that he could have eaten it," Karlee told Nine News.

Speaking to Mamamia, a Kellogg's spokesperson said that Kellogg's cereals are still completely safe to eat.

"We're in contact with a consumer who has let us know she found a tablet in her Coco Pops," they said.

"Along with manufacturing based on strict quality standards, we also have policies in place that prohibit employees bringing medications into the plant. We are doing a full investigation with our team and are staying in touch with the consumer," they continued.

"Based on the available information, our food on the shelf is safe to eat."

Kellogg's have since sent the capsule for testing and will receive results in the next few days.

"Based on the information we have, which includes the image provided by the consumer and our conversation with the manufacturer of the medication, we believe it is Duromine," a Kellogg's spokesperson said.

"Our investigation found that none of the team who made this food use Duromine. It is a highly controlled prescription-only medicine. Based on this information it is highly unlikely that this happened at our factory. We manufacture all our foods to strict quality standards and want to reassure people that Coco Pops is safe to eat.

"We have not received any more complaints on this issue."