Mr. Speaker, absolutely, any per se limit should be based upon science. One of the real issues is that there is not a clear correlation between drug impairment and THC limits. For example, long-term habitual users of THC will tend to have higher levels of THC because THC will remain in their bodies; whereas someone who may have just consumed marijuana but is not a habitual user and gets behind the wheel may record relatively low levels of THC. Therefore, one of the difficulties is the fact that someone who is impaired might not be caught by the per se limit, whereas someone who is not impaired might be caught, and that is a problem.
In the House of Commons on October 20th, 2017. See this statement in context.