It’s certainly a good excuse to have when you’re slumped on the sofa and feel like you’re simply obliged to finish off that shiny tin of Quality Street.

Chocolate has an effect on the brain similar to opium, according to a study that found amazing comparisons between obese people and drug addicts.

In the study, a natural brain chemical called enkephalin – an endorphin with similar properties to opium – surged as rats began to eat M&M chocolates.

When a drug was used to stimulate the dorsal neostriatum – the brain area releasing the chemical – the number of M&Ms eaten more than doubled.

In the brain, enkephalin binds to molecular ‘receptors’ sensitive to opiate chemicals to reduce pain and produce pleasurable feelings.

Previous research mostly linked the dorsal neostriatum to movement, and recent work suggested it also plays a role in reward-driven behaviour.

Dark chocolate

But study leader Dr Alexandra DiFeliceantonio said the extraordinary findings showed comparisons between and drug addicts and the obese.

She said: ‘This (study) means that the brain has more extensive systems to make individuals over-consume rewards than previously thought.

‘The same brain area tested here is active when obese people see foods and when drug addicts see drug scenes.

‘It seems likely that our enkephalin findings in rats mean that this neurotransmitter may drive some forms of overconsumption and addiction in people.’

The findings of the University of Michigan researcher and her team have been published in the US journal Current Biology.

In their paper, the scientists concluded: ‘Opioid circuitry… could in this way participate in normal motivations and perhaps even in generating intense pathological levels of motivation to overconsume reward in binge eating disorders, drug addiction and related compulsive pursuits.’