Change your preferences here.
The user loses HP equal to 1/2 of the damage dealt to the opponent, rounded down. Struggle is only used when a Pokémon is unable to use any other move.
If the user faints after using this move and attacking first, then the opposing Pokémon doesn't attack. It does not lose 1 PP for the move it was going to use. In addition, it will not receive damage from being poisoned or burned, and the effect of Leech Seed will not trigger. Struggle does not affect Ghost Pokémon.
I'm struggling to think of any reason you'd want to voluntarily use this move, let alone use it competitively.