You can't generate "waveforms" with a regular Arduino because there is no DAC. (Analog can be "simulated" under some conditions with PWM for motor speed control or LED dimming.)
A transformer is going to make it harder...
If the DAC can't put-out negative voltages, you can bias the DAC output then you can either use a summing amplifier to sum-in a negative voltage, or in the case of AC signals (where you don't have to "hold" positive or negative signals) you can use an RC high-pass filter. The DC bias is zero-Hz, and a high-pass filter will remove it. A capacitor is often used on audio outputs to remove the bias.
I believe that peak voltages are ≈2V/-2V.
It's hard for me to believe that such a low voltage will do anything. (But, I'm not a doctor or a biologist.) Anything over 50V is generally considered dangerous by the regulatory agencies. But it's not the voltage that's directly dangerous, it's the resulting current. (I assume you are familiar with Ohm's Law?)