46 CFR § 10.301 - General requirements.
(a) The Coast Guard will issue a medical certificate to a mariner meeting the medical and physical standards for merchant mariners. The medical certificate will be issued for various periods of time based upon the endorsements the mariner holds. The Coast Guard will review all information provided and will determine whether—
(1) The applicant is physically and medically qualified for the medical certificate without any limitations, waivers and/or other conditions;
(2) The applicant is physically and medically qualified for the medical certificate with limitations and/or other conditions as specified by the Coast Guard;
(3) For an applicant who does not possess the vision, hearing, or general physical condition necessary, a medical certificate may be issued with appropriate limitations, waivers and/or other conditions as specified by the Coast Guard;
(4) Additional information is necessary to determine if the applicant is physically and/or medically qualified for the medical certificate. The Coast Guard will request additional information from the applicant. The Coast Guard may hold the package pending receipt of that information before the package and/or application is denied; or
(b) Except as otherwise noted, medical certificates will be issued for the following periods of time:
(1) All persons employed or engaged onboard vessels to which STCW applies will be issued a medical certificate valid for 2 years unless the mariner is under the age of 18, in which case the maximum period of validity will be 1 year.
(2) Medical certificates issued to all other mariners will be issued for a maximum period of 5 years.
(c) Applicants seeking additional MMC endorsements holding a current medical certificate are not required to submit a new medical physical exam if their existing medical certification meets all of the requirements of this section for the endorsement sought.