Medical certification in accordance with Federal Motor Carrier Safety Administration (FMCSA) physical qualification standards is required when the driver is operating a commercial vehicle in interstate commerce that:
When a driver returns from an illness or injury that interferes with driving ability, the driver must undergo a medical examination even if the medical examiner's certificate has not expired.
The medical examiner is responsible for certifying only drivers who meet the physical qualification standards. Certification cannot exceed 2 years, and at the discretion of the FMCSA medical examiner, may be less than 2 years. The Federal Vision and Diabetes Exemption Programs require annual medical certification.
The medical examiner's certificate expires at midnight of the day, month, and year written on the certificate. There is no grace period on the expiration. The driver must be re-examined and re certified to continue to drive legally.
sources :Federal Motor Carrier Safety Administration (FMCSA) Medical Examiner Handbook