A key component of medical marijuana could provide an “entirely new” type of treatment for mental health patients suffering with hallucinations and delusions.

The first clinical trial exploring the effects of cannabidiol (CBD), one of the major psychoactive compounds in cannabis, found that it could relieve symptoms in patients with psychosis.

CBD has a broadly opposite effect to delta-9-tetrahydrocannabinol (THC), the main active component  in cannabis and the substance that causes paranoia and anxiety.

It also doesn’t cause a high so has little recreational benefit.

This has led to CBD being studied as a potential therapy for mental health conditions, epilepsy, and in Parkinson’s disease, or chronic pain.

Psychosis is a mental health diagnosis characterised by hallucinated voices or visions, or delusions where patients have strong and unfounded beliefs, for example feeling there is a conspiracy to harm them.

Antipsychotic drugs have been used in treating it for 60 years, but they have limited effectiveness and can have serious side-effects.

Professor Philip McGuire, from King’s College London’s Institute of Psychiatry, Psychology and Neuroscience, was the lead author of the study.

He said conventional drugs acted by blocking biological receptors for mood-altering chemical dopamine.

“However, dopamine is not the only neurotransmitter whose function is altered in psychosis, and in some patients dopamine function may be relatively normal,” he added.