[soundwave106]

There does seem to be some links between the endocannabinoid system (the primary target of marijuana) and the serotonin system (the primary target of LSD). EG:

http://www.ncbi.nlm.nih.gov/pubmed/17944876 http://www.jneurosci.org/content/27/43/11700.abstract

From what I can see, the relationship isn't terribly clear at this time. As dopamine and serotonin systems are linked to schizophrenia, until more is known, I personally think anyone with even mild signs of schizophrenia would do best to avoid chemicals like marijuana, LSD, stimulants, etc.