In March Consumer NZ said there was no evidence the Pain Erazor did what its marketing company claimed.
The company, Brand Developers, said the $160 unit worked by exerting pressure on a quartz crystal, which produced a tiny electric charge.
According to the company's website, when the pen is clicked against the point of pain about 30 or 40 times the body's endorphins are stimulated, acting as a natural pain killer.
Brand Developers claimed the pain relief provided, "electro-analgesia", was similar to TENS but had a "more effective, longer-lasting pain killing effect than a regular TENS unit".
Consumer NZ has investigated the pen in its March newsletter, with the consumer watchdog acknowledging this type of pain relief was possible.
However, it said Pain Erazor provided no evidence the pen had been successfully shown to work.
Consumer NZ said there was nothing in the product's 116-page booklet which showed this had been proven in trials.