Some of 61.53
doesn't apply to Basic Med, notably (a), which applies only to operations that require a medical certificate. Below that (b) applies to Basic Med, since operations require a driver's license. But the standards are different, i.e. one applies to "meeting the requirements of the medical certificate" and the other applies to being able to "operate the aircraft in a safe manner".
There's a big difference between certification and operation, with Part 61 covering certifications and Part 91 covering operations.
§ 61.53 Prohibition on operations during medical deficiency.
(a) Operations that require a medical certificate. Except as provided for in paragraph (b) of this section, no person who holds a medical certificate issued under part 67 of this chapter may act as pilot in command, or in any other capacity as a required pilot flight crewmember, while that person:
(1) Knows or has reason to know of any medical condition that would make the person unable to meet the requirements for the medical certificate necessary for the pilot operation; or
(2) Is taking medication or receiving other treatment for a medical condition that results in the person being unable to meet the requirements for the medical certificate necessary for the pilot operation.
(b) Operations that do not require a medical certificate. For operations provided for in § 61.23(b) of this part, a person shall not act as pilot in command, or in any other capacity as a required pilot flight crewmember, while that person knows or has reason to know of any medical condition that would make the person unable to operate the aircraft in a safe manner.
(c) Operations requiring a medical certificate or a U.S. driver's license. For operations provided for in § 61.23(c), a person must meet the provisions of—
(1) Paragraph (a) of this section if that person holds a medical certificate issued under part 67 of this chapter and does not hold a U.S. driver's license.
(2) Paragraph (b) of this section if that person holds a U.S. driver's license.
On the other hand, 91.17 (c) prohibits operating while using
any drug contrary to safety, which includes Benadryl and other over-the-counter drugs as well as opiods, hallucinogenics, and other obvious candidates for that restriction.
§ 91.17 Alcohol or drugs.
(a) No person may act or attempt to act as a crewmember of a civil aircraft—
(1) Within 8 hours after the consumption of any alcoholic beverage;
(2) While under the influence of alcohol;
(3) While using any drug that affects the person's faculties in any way contrary to safety; or
(4) While having an alcohol concentration of 0.04 or greater in a blood or breath specimen. Alcohol concentration means grams of alcohol per deciliter of blood or grams of alcohol per 210 liters of breath.