21 CFR §1315.33

1. (a)A registrant may authorize one or more individuals, whether or not located at his registered location, to sign certifications required under § 1315.32(h) on the registrant's behalf by executing a power of attorney for each such individual. The registrant shall retain the power of attorney in the files, with certifications required by § 1315.32(h), for the same period as any certification bearing the signature of the attorney. The power of attorney must be available for inspection together with other certification records.
2. (b)A registrant may revoke any power of attorney at any time by executing a notice of revocation.
3. (c)The power of attorney and notice of revocation must be similar to the following format:
4. (d)A power of attorney must be executed by the person who signed the most recent application for DEA registration or reregistration; the person to whom the power of attorney is being granted; and two witnesses.
5. (e)A power of attorney must be revoked by the person who signed the most recent application for DEA registration or reregistration, and two witnesses.