Tasers are capable of an output of 50,000 volts, but the voltage delivered to the body is only 1,200. The initial high voltage is used to establish a current between the two taser barbs. Immediately after contact with a body occurs, the voltage drops.
Although tasers use high voltages, the current is low. This protects the person who is being shocked, as high currents are much more dangerous than high voltages. One comparison of the relative dangers is that static shocks rarely cause much damage, even though the voltages may be higher than 30,000 volts due to the extremely low currents from these shocks.