Cannabis is often combined with MDMA to lengthen the effects of the E. There have not been many reports of an immediate increases in risk so far, except that it seems to lead to more psychological complaints like anxiety, depression, and obsessive-compulsive behaviour.

You should NOT drive though; pot changes your perception of motion in a vehicle, and when the effect of using E with cannabis was tested in driving simulators, it got a lot worse. It really blows your ability to drive safely.

Also, memory, learning, word fluency and how fast you can think are worse in MDMA/THC users than in users of cannabis alone. The longer you use, the more obvious the impairment becomes.