The Lancet Journal published a study in 2007 definitely linking psychosis later on in life with earlier Marijuana use.

Lancet. 2007 Jul 28;370(9584):319-28.
Cannabis use and risk of psychotic or affective mental health outcomes: a
systematic review.
Moore TH, Zammit S, Lingford-Hughes A, Barnes TR, Jones PB, Burke M, Lewis G.
BACKGROUND: Whether cannabis can cause psychotic or affective symptoms that
persist beyond transient intoxication is unclear. We systematically reviewed the
evidence pertaining to cannabis use and occurrence of psychotic or affective
mental health outcomes. METHODS: We searched Medline, Embase, CINAHL, PsycINFO,
ISI Web of Knowledge, ISI Proceedings, ZETOC, BIOSIS, LILACS, and MEDCARIB from
their inception to September, 2006, searched reference lists of studies selected
for inclusion, and contacted experts. Studies were included if longitudinal and
population based. 35 studies from 4804 references were included. Data extraction
and quality assessment were done independently and in duplicate. FINDINGS: There
was an increased risk of any psychotic outcome in individuals who had ever used
cannabis (pooled adjusted odds ratio=1.41, 95% CI 1.20-1.65). Findings were
consistent with a dose-response effect, with greater risk in people who used
cannabis most frequently (2.09, 1.54-2.84). Results of analyses restricted to
studies of more clinically relevant psychotic disorders were similar. INTERPRETATION: The evidence
is consistent with the view that cannabis increases risk of psychotic outcomes
independently of confounding and transient intoxication effects. We conclude that there is now
sufficient evidence to warn young people that using cannabis could increase their
risk of developing a psychotic illness later in life.