A number of verdicts can be returned in an inquest, including dependence on drugs/non-dependant abuse of drugs, suicide (or killed him/herself) whilst the balance of his/her mind was disturbed, lawful and unlawful killing and an open verdict (where the cause of death cannot be established and doubt remains as to how the deceased came to their death).
The coroner will return a verdict ‘killed him or herself’ if it is believed on the basis of factual evidence that the person genuinely intended to kill themselves. However, there has to be clear evidence, for example a suicide note. If they did something that resulted in their death but there is not enough evidence that they intended to die, this verdict cannot be returned.
Taken from verdicts on the Inquest site