It has been stated by a British study that a person does not commit violent crimes due to severe mental illness alone. The cause for this as described by researchers from Oxford University is substance abuse.

It was also noted by researchers that there was a 10 times more chance of alcohol and drug abuse among people suffering from bipolar disorder or schizophrenia.

The perception among people that a person suffering from mental illness acts violently is completely false, study leader Dr Seena Fazel stated.

He added, "People with bipolar disorder, if they abuse drugs, are at increased risk. But so are people in the general population if they use or abuse drugs or drink alcohol to excess.”

People who are mentally ill are more inclined to indulge in drug and alcohol abuse and this is possibly due to ameliorate the unpleasant side-effects of powerful psychiatric medicines that increase the risk of violence.

Among both general and mentally ill people, substance abuse increased the risk of violence by between six and seven times.