Electrotherapy has been around for hundreds of years, and not only does ancient science support it, but modern research suggests that in certain circumstances it is a safe and effective way to elimate headaches, some seizure disorders, and even certain psychiatric conditions. It is worth studying more to evaluate it's effectiveness.
There is very little evidence for the efficacy of electrotherapy, even in this day and age. And because there is still no conclusive evidence for its efficacy, I am led to believe that it is probably not a very reliable method of treatment. The fact that it has been used for so many years, is not, in my opinion, proof of its efficacy. For a very long time, people in ancient times believed that the earth was flat. The fact they held that belief for so long, did not prove that the belief was correct. In fact, as we all know, it was proven to be very incorrect.
Though electrotherapy has been used in some way or another for centuries, this does not make it a good choice for medical treatment. It has been shown to damage brain cells, specifically the ones that process memory. Therefore anyone who undergoes this form of treatment is losing as much as they are gaining.
In medieval times people would bleed the sick to drain the bad blood from their bodies. Superstition and a poor understanding of anatomy led to many ineffective ways to deal with mental and physical illnesses. That doesn't mean that electrotherapy won't work, just using a precursor as an argument is a bad idea.