There is an investigation to look at all aspects of the situation IF it involves death. They will look at finances, personal life, recent tragedy, all of these would be motive to end it all. They interview friends and family, business associates, anyone that is close to the person. based on this and the drug that was involved, they can get a good idea if it was intentional of accidental.
-
When someone commits suicide by overdose, they usually overdose by A LOT so it's obvious. Accidental can be tricky sometimes though in the case of pills that can cause short-term memory loss, like sleeping pills because a person may forget how many they've had and just keep going, but this does not usually happen.
-
Quantity of pills taken. Nobody "accidentally" takes 10 or 20 pills or more. Nobody. When someone takes that many pills, that is a suicide attempt, no matter how much they may later deny it.
-
Suicide