The US Food and Drug Administration has determined how much Gaussian magnetic field is a medical device.

Below 0.5 gauss. Because the magnetic field intensity higher than 0.5 gauss may cause potential risks to human health, the main responsibility of the Food and Drug Administration is to protect public health and safety. According to clinical research and medical evidence, the Food and Drug Administration will determine that the magnetic field below 0.5 gauss has certain medical effects on treating some diseases or symptoms, so it is determined that the magnetic field below 0.5 gauss is a medical device product.