Cannabis use does not affect teenager's IQ, new research reveals.

Taking the drug between the ages of 12 and 18 does not cause adolescent's intelligence to decline, a study found.

Yet, children with low IQs are more likely to use cannabis as teenagers, the research adds.

Drug researcher Ian Hamilton from York University told MailOnline: 'This research murders an age-old myth about cannabis.'

Previous studies have revealed cannabis use affects teenager's educational achievements, as well as increasing their risk of depression and psychosis.

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Using cannabis between the ages of 12 and 18 does not cause adolescent's IQ to decline

MARIJUANA USE INCREASES THE RISK OF DYING FROM HIGH BLOOD PRESSURE BY MORE THAN THREE TIMES Marijuana use increases the risk of dying from high blood pressure by more than three times, research revealed last month. This risk increases by more than one time for every year of cannabis use, a study found. Results suggest marijuana use is more dangerous for heart health than cigarettes, despite certain campaigners insisting cannabis is safer than tobacco. Experts argue the findings are particularly important given marijuana's legalization in eight US states, including Alaska, California and Colorado. Lead author Barbara Yankey from Georgia State University, said: 'It is important to establish whether any health benefits outweigh the potential health, social and economic risks.' Advertisement

How the research was carried out

Researchers from Arizona State University analyzed 1,989 twins born in England and Wales between 1994 and 1995.

The study's participant's cannabis use was assessed at 18 years of age.

Their IQ was determined at five, 12 and 18.

'Murders an age-old myth about cannabis'

Results reveal cannabis use between the ages of 12 and 18 does not cause IQ to decline.

Mr Hamilton said: 'This research murders an age-old myth about cannabis.

'For many years parents and teenagers have been warned about the harmful effects cannabis can have on their brains and education but this research found that short term use of cannabis by teenagers does not reduce their IQ even when they become dependent on the drug.

'By measuring children's IQ before they start using cannabis the researchers were able to show that it was not cannabis that was associated with a decline in IQ but other factors such as their family environment and social circumstances.'

Yet, the findings also revealed teenage cannabis users had lower childhood IQs than non-users prior to starting their marijuana habit.

They also have a lower IQ at 18.

The findings were published in the journal Addiction.

Past study shows cannabis affects educational achievements

The latest results contradict findings by from the University of Pittsburgh that revealed teenagers who increase their marijuana use with age have a greater risk of depression, an inability to experience pleasure and poor educational achievements in later life.

Men who infrequently use cannabis at age 15 but dramatically increase their use up to 19 years old, are more at risk than those who consistently take the drug throughout their teens, the study found.

Scientists at the University of Montreal also found that going from being an occasional marijuana user to indulging every day increases the risk of psychosis by up to 159 percent.

Marijuana is thought to cause psychosis-like experiences by increasing a user's risk of depression, the study found The two mental health conditions have previously been linked.

Frequently abusing the substance also significantly reduces a user's ability to resist socially unacceptable behavior when provoked, the research adds.