A hallucinogenic drug is a drug that causes hallucinations or illusions, usually visual, together with personality and behavior changes. The last may arise as a result of therapy, but more usually follow deliberate exposure to certain drugs for their psychological effects ("trip"). Lysergic acid diethylamide (LSD), heroin, morphine, and other opium narcotics, mescaline, and psilocybin are commonly hallucinogenic and cannabis sometimes so. The type of hallucination is not predictable and many are unpleasant ("bad trip"). Recurrent hallucinations may follow use of these drugs; another danger is that altered behavior may inadvertently cause injury or death. Although psychosis may be a result of their use, it may be that recourse to drugs represents rather an early symptom of schizophrenia.