Users of illicit drugs and heavy drinkers tend to underestimate their levels of consumption when comparing themselves to others, a new study has found.

UK researchers analysed the findings of the 2012 Global Drugs Survey (GDS), which is the world's biggest drug survey. They focused on the replies given by almost 7,800 people living in the UK.

They found that while 68% of respondents were consuming alcohol at harmful or hazardous levels, 83% of these felt they were consuming alcohol at low or average levels.

The same pattern was found when it came to illicit drug use. For example, among those who smoked cannabis every day or most days, one-third considered this to be average or less than average.

When it came to cocaine and ecstasy, over half of even the heaviest users felt they were consuming an average amount.

"Given that drug use carries certain risks, whether this be to health, of getting caught or of damage to reputation, we shouldn't be surprised that some people downplay their levels of use as a way of managing their anxieties about what they're doing," commented Dr Michael Shiner of the London School of Economics, who was an expert advisor to the GDS.

The research also found that at least one in three respondents wanted to reduce their existing levels of alcohol consumption, while one in four wanted to reduce their use of illicit drugs.

Heavier users of these substances, and those who viewed themselves as heavier users, were more likely to want to reduce their consumption compared to those who consumed less or believed they consumed less.

In fact, those who thought they were drinking high levels were almost twice as likely to want to cut down, irrespective of their actual drinking levels. Similar results were found in relation to cannabis, cocaine and ecstasy use.

The 2016 GDS launches next month.

Details of these findings are published in the journal, Social Science and Medicine.