Psychedelic drugs changes one's mood, behaviour, thoughts, feeling and perceptions, without any true sensory stimulus. They cause hallucinations [a sense perception (sight, touch, sound, smell or taste) that has no basis in external stimulation]. LSD causes horrible dreams, emotional outbursts, hallucination, chronic psychosis and severe damage to the central nervous system. It also brings about chromosomal and foetal abnormalities. An LSD addict can be easily recognised from incoherence in writing and drawing.

Use of alcohol, vision becomes blurred and unsteady often the field of vision is reduced called Tunnel vision.

Accumulation of fat in the liver of the alcoholics result from the combination of impaired fatty acid oxidation, increased uptake and esterification of fatty acids to form triglycerides and diminished lipoprotein biosynthesis and secretion. Lipoproteins may also accumulate in the liver. Fatty liver syndrome is a condition of permanent damage to the structure and functioning of liver cells.

Indoor atmospheres and other confined spaces are often contaminated by tobacco smoke which is inhaled involuntarily by both smokers and nonsmokers. It is called involuntary smoke inhalation or passive smoking. It is now recognized as a cause of lung cancer in nonsmokers.

Social therapy of mental illness is required for rehabilitation of mentally ill persons.