Final answer:
Pilots must prioritize safety and are generally not allowed to permit someone under the influence of drugs onto an aircraft, except for specific exceptions such as medical emergencies.
Step-by-step explanation:
Regarding the conditions under which a pilot may allow a person who is obviously under the influence of drugs to be carried aboard an aircraft, safety and legal regulations largely prohibit such a situation. However, exceptions could be made in cases where the individual needs to travel for urgent medical treatment and does not pose a safety risk, or if the individual is accompanied by a handler or medical professional responsible for their condition. But, generally, aviation regulations are strict in ensuring the safety and security of all passengers, and someone under the influence could be seen as a potential risk.