London, (IANS) A single dose of cocaine interferes with a person's ability to recognise negative emotions such as anger and sadness, says a new study.

The researchers found that a single dose of cocaine caused an increased heart rate as well as increased levels of the stress hormone cortisol.

In addition, it was found that the subjects who took cocaine found it more difficult to recognise negative emotions.

"This is the first study to look at the short-term effect of cocaine on emotions," said lead researcher Kim Kuypers from Maastricht University in the Netherlands.

A single cocaine dose might hinder the ability to interact in social situations.

"But it may also help explain why cocaine-users report higher levels of sociability when intoxicated - simply because they cannot recognise the negative emotions," Kuypers said.

In a placebo-controlled study, researchers from the Netherlands and Germany took 24 students (aged 19 to 27) with light to moderate cocaine use, and gave them either 300 mg of oral cocaine or a placebo.

After one-two hours, each participant was then subject to a series of biochemical tests, as well as the facial emotion recognition test to measure response to a series of basic emotions, such as fear, anger, disgust, sadness, and happiness.

The subjects who took cocaine found it more difficult to recognise negative emotions.

They also found that the subjects who showed a larger cortisol response after taking cocaine had a less marked impairment of negative emotions.

When they were intoxicated with cocaine, their performance was 10 percent worse compared to their performance during placebo, in recognising sadness and anger.

"Since cocaine changes the level of the brain chemical dopamine, this study may have implications for other mental illnesses such as depression and schizophrenia - where dopamine may also be involved in how we recognise emotions," said Michael Bloomfield from University College, London.

The findings were presented at the ECNP conference in Amsterdam on August 29