THC was the prime factor.
The use of marijuana in its various forms is under considerable debate in the U.S. Some states have nullified federal law and are allowing marijuana to be sold legally for medical purposes. Other jurisdictions have decriminalized marijuana held for personal use and, at worse, made its possession a simple violation similar to failing to signal a turn while driving.
It is important for pilots to understand that substances containing THC can reduce cognitive functioning. Not only is physical performance degraded, but judgment can be affected for long periods after THC enters the bloodstream. And, more important, the user may not realize the effects remain more than 24 hr. after its use.
As the general public and even laws become more tolerant of THC-containing substances, pilots must remain especially wary of their use for medical or recreational purposes.