The limits for both THC, the primary psychoactive drug in cannabis, and THCA, its main metabolite, are each set out in a schedule inserted by section 8 (c) of the Road Traffic Act 2016. The legal limit for 9 Tetrahydrocannabinol (THC) is 1ng/ml in blood while the legal limit for 11-nor-9-Carboxy- 9 Tetrahydrocannabinol (THCA) is 5ng/ml in blood.
I refer the Deputy to the parliamentary debates surrounding the passage into law of that particular section by these Houses in 2016, debates in which the rationale for these limits was discussed in some detail. As was made clear by my predecessor as Minister for Transport at that time, these limits were decided upon in line with the most robust and up to date scientific evidence.
The chemical testing of intoxicants in driving is the statutory responsibility of the Medical Bureau of Road Safety (MBRS) and I have therefore forwarded the second part of the Deputy's query to the Bureau for direct response. I would ask that he contact my office if no reply is received within 10 working days.