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Subjects who were using cannabis during the 6-month observation period presented with a significantly higher degree of delusional and hallucinatory activity than those who did not. Moreover, the group using cannabis made a higher average number of visits to the hospital during the same period. The status of cannabis use appeared to contribute to such variance more than did other relevant factors (age, stage of the illness, amount of medication prescribed, occasional use of other psychoactive substances).<\/jats:p>","DOI":"10.1017\/s0033291700010278","type":"journal-article","created":{"date-parts":[[2009,7,9]],"date-time":"2009-07-09T10:44:53Z","timestamp":1247136293000},"page":"515-520","source":"Crossref","is-referenced-by-count":180,"title":["Cannabis affects the severity of schizophrenic symptoms: results of a clinical survey"],"prefix":"10.1017","volume":"16","author":[{"given":"Juan C.","family":"Negrete","sequence":"first","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Werner P.","family":"Knapp","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Donald E.","family":"Douglas","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"W. 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