The US Food and Drug Administration (FDA) has permitted the use of implantable ID chips in humans, despite an FDA investigator's recent public reservations about the devices.

The FDA has told chip manufacturer Applied Digital Solutions (ADS) that it will not regulate the VeriChip if it is used for "security, financial and personal identification or safety applications".

But the agency has not determined whether the controversial chip can be used for medical purposes, including linking to medical databases.

ADS has principally marketed VeriChip as a life-saving tool, claiming that unconscious patients brought to an emergency room could be scanned to obtain their medical histories from it.

The company made international headlines by implanting three members of a Florida family with the VeriChip, which is slightly larger than a grain of rice and emits a 125KHz radio frequency signal that can be picked up by a scanner up to four feet away.

However, the FDA's backing is surprising, as in an interview with Wired magazine an investigator from the agency said he was unaware of any implantable device that was not regulated by the FDA. Cosmetic implants have to undergo a rigorous FDA examination to determine their effect on the human body despite having no medical function.

Although ID chips have been used in animals for years, they may have "inherent risks" when used in humans, the investigator said.