Basically, there is clear evidence that marijuana and smoking marijuana can trigger mental disorders—for example, psychotic symptoms and schizophrenia, as has been shown—in vulnerable people. That means that overall we do have this connection.
This is not a very frequent connection. If you look into the deaths and the very serious events related to marijuana, the most important effect on mortality is actually traffic—that means smoking marijuana and being in traffic—and lung cancer. That has the same effect as smoking cigarettes, albeit, of course, on a way smaller scale, because marijuana is smoked by fewer people.