Final answer:
Schedule I drugs such as heroin and LSD cannot be dispensed as they are deemed to have no accepted medical use and a high potential for abuse. Controlled substances like opium, fentanyl, and oxycodone are regulated but can be dispensed under strict regulations given their medical use.
Step-by-step explanation:
The question regarding controlled drugs that cannot be dispensed under any circumstances pertains to substances that are categorized under Schedule I according to the Controlled Substances Act. Schedule I drugs are considered to have a high potential for abuse, no currently accepted medical use in treatment in the United States, and a lack of accepted safety for use under medical supervision. Therefore, drugs such as heroin, LSD, mescaline, and MDMA, which are classified under Schedule I, cannot be prescribed or dispensed legally for medical use. It is important to note that substances like opium, fentanyl, morphine, oxycodone, Vicodin, methadone, and other prescription pain relievers are not listed as Schedule I substances. Instead, they are usually regulated under Schedule II due to their recognized medical uses and are dispensed under strict regulations. Prescription or over-the-counter medicines taken in doses that are too high can lead to overdoses but these do not fall under the 'cannot be dispensed under ANY CIRCUMSTANCES' category unless they are specifically Schedule I substances.