Sure THC can trigger a mental condition, but you have to keep in mind that anything can trigger a mental condition. It's a non-point to make. If a person actually has an underlining mental condition, it will make itself apparent at some point in their life... and it's impossible to say what thing will actually trigger it. This is just pro-drug war peoples' way of getting people afraid of smoking pot, plain and simple.

A commute to work one day may in fact be stressful enough to trigger an underlining mental illness. Are you planning on never going to work again now that you know that? I wish I never had to!