The device should not have been medically tested as the vibrations are too strong and shake the whole body and not locally, resulting in huge vibrations in the joints and spine. Also, the head is made of plastic, which I find unacceptable for its use. It is very heavy and you cannot hold it for more than three minutes. It does not have instructions. It does not have an indication of whether it is allowed for pregnant women or individuals with extremity disorders... which with its characteristics, I would not recommend it.