Herbal cannabis cultivated in sophisticated grow houses across Ireland is more likely to cause psychosis than imported herb and resin, it has emerged.
Forensic tests showed skunk or weed produced from cannabis factories have higher levels of the psychoactive component tetrahydrocannabinol (THC).
Scientists at the Forensic Science Laboratory (FSL) said the home-grown drug also has low levels of the substance cannabidiol (CBD), which counteracts the effects of THC. The National Advisory Committee on Drugs (NACD) raised serious concern about the surges in cannabis cultivation in Ireland.
Dr Des Corrigan, chairman of the NACD, said: "Many of the plants being grown here are genetically selected to ensure they produce high levels of THC but they also lack a substance called CBD, which seems to protect the brain from the effects of THC, which can include psychosis.
"Samples from seizures of the cannabis herb in Limerick, Cork, Tipperary, Bandon, Fermoy and Dublin - including Ronanstown, Dundrum, Tallaght and Crumlin - found that cannabis which was of Irish cultivation had very high THC levels and very low CBD levels compared to imported herb and resin (hash)."
Cannabis remains the most commonly used illicit drug in Ireland, but can not be grown outdoors because of Ireland's climate. Instead, plants are cultivated indoors using state of the art hydroponics and intensive lighting equipment.
Approximately 20,000 cannabis plants have been seized in the sophisticated grow houses nationwide in recent years, including 800 plants uncovered by gardai in Dundalk, Co Louth, on Monday. One of the largest ever hauls of 1,500 cannabis plants was discovered in a rented house in Kyletalesha, near Portlaoise, Co Laois, in September - the same day up to 500 cannabis plants at various stages of growth were found in a sophisticated growing operation in Co Louth.
Dr Corrigan warned that in many cases, female rather than male plants are used as they cannot then produce seeds, meaning all of the energy within the plant goes into the production of THC content, increasing the plant's potency.
"The high quantity of THC in cannabis raises serious health concerns as recent UK studies has shown that there is a higher risk of psychosis in those who smoke high-potency cannabis products compared to those who smoke hash which contains both THC and CBD," he added.
"While it is the high THC content and frequency of use of the former products that may cause psychotic episodes, it is also thought to be attributed to the amount or lack thereof of CBD, as CBD appears to decrease the effects of THC when ingested together."