I'm aware that cannabis use by folk with predispositions to conditions such as schizophrenia can lead to heightened psychotic effects, but am not so sure about the mixing of cannabis and psychedelics being dangerous in this way, other than for those with underlying conditions.

Sure, cannabis can amplify the effects of psychedelics, leading to people becoming overwhelmed or having a 'bad trip', but much of this could also be attributed to a lack of preparation and a proper intention and setting, and does not seem to lead to long term problems.

It seems pretty clear that Bertaraja made a fairly unwise decision in taking the combination they did, especially knowing the negative effect weed has on them already, but from the, albeit, brief bit of searching I have just done on the subject, it doesn't seem that cannabis taken with psychedelics causes long term psychotic problems like these, except in the case of preexisting conditions, or, at least, there is little but anecdotal evidence of this.