Smoking just half a joint of cannabis can cause psychosis-like effects similar to schizophrenia, scientists have claimed.

It has been known for a long time that cannabis can cause anxiety, paranoia and loss of motivation. But researchers at Yale School of Medicine found that delta-9-tetrahydrocannabinol (delta-9-THC) – the active ingredient in cannabis – can trigger symptoms which are normally associated with schizophrenia.

This could include experiencing hallucinations and delusions as well as feeling suspicious, depressed and withdrawn.

The study found that delta-9-THC increased the level of neural noise in the brains of healthy drug users even when they had smoked as little as half a joint. This increased noise can disrupt the way the brain processes information.

Professor of psychiatry at Yale, Dr Deepak D’Souza, who was involved in the study, said: “At doses roughly equivalent to half or a single joint, delta-9-THC produced psychosis-like effects and increased neural noise in humans.”

Ingredient in cannabis disrupts brain activity

The electrical brain activity of 24 people was studied over three days to examine the impact of delta-9-THC. Those taking part were either given two intravenous doses of delta-9-THC or a placebo.

Dr John Krystal, editor of Biological Psychiatry, which published the study, said: “This interesting study suggests a commonality between the effects on the brain of the major active ingredient in marijuana and symptoms of schizophrenia.

“Not only does this finding aid our understanding of the processes underlying psychosis, it underscores an important concern in the debate surrounding medical and legalised access to marijuana.”

The results of this research suggest even casual or occasional cannabis use could be more dangerous than many people assume. By causing difficulties in concentration and changes in mood, smoking the drug could affect people’s ability to do their jobs properly and safely.

AlphaBiolabs offers drugs tests for employers so they can find out whether members of their workforce are misusing the drug. We also provide legal drug testing for courts and official organisations as well as peace of mind tests for friends and family.