The electric stun gun tricks the muscles of an attacker, making them do a great deal of work rapidly. This instantly depletes the attacker's blood sugar by converting it to lactic acid. In short, he is unable to produce energy for his muscles, and his body becomes unable to function. This process is what makes electronic stun guns so simple yet effective.
 
Electric stun guns do not rely on high amperage, or pain, for results.
 The gun is designed to key into the nervous system.  It interrupts the tiny neurological impulses that travel through the whole body to control and direct voluntary muscle movement.  When the assailant's neuromuscular system is overwhelmed and controlled by the electronic stun gun, instant disorientation and loss of balance will result.

Using electric stun guns are not dangerous. Should the assailant be touching you, the current will not pass to your body!  Stun guns are a great protection device, but you should always be aware that these devices are not toys, and should not be treated as such.