SYDNEY -- Australia and New Zealand's food regulator on Monday warned people not to consume drinks claiming to enhance sexual performance as they may contain a substance similar to the drug Viagra.

Food Standards Australia New Zealand (FSANZ) issued the warning on Monday, saying analysis by government authorities has shown two coffee products ?-- "expresso" and "Rock Hard" -- contain analogues of sildenafil (Viagra).

"These analogues, like any drugs can interact with prescription medicines and may be dangerous, particularly for people with certain health conditions," FSANZ stated in the warning.

"Consumers who are using this product should stop taking it immediately and speak to a doctor if they are experiencing side effects," FSANZ said.

The watchdog said the drug was not declared on the drinks' labels and it was unknown what side effects it could produce.

"State and territory food enforcement agencies are currently investigating the products, which are being sold as an instant coffee product, and have been available on the internet and in adult shops," the food regulator said.

The FSANZ warning follows the recall of several foods in the past six months because they contained prescription medicines.

"Consumers should be cautious of food products that make claims about treating physical conditions," FSANZ said.

"They should speak to their doctor before taking these products as even natural products can interfere with prescription medicines. "