Which of the following substances falls under Schedule I?

Schedule I substances are classified as having a high potential for abuse and no accepted medical use in the United States. This classification is part of the Controlled Substances Act. LSD, or lysergic acid diethylamide, is considered a Schedule I substance because it is widely recognized for its potential for abuse, and it has no accepted medical uses in treatment as approved by the FDA. This means that while it can produce significant effects on perception, mood, and other mental processes, it poses a high risk of addiction and is not safe for medical use under federal regulations.

In contrast, fentanyl, oxycodone, and morphine are classified as Schedule II substances. Schedule II drugs are recognized to have therapeutic uses but carry a high potential for abuse and dependence. These substances can be prescribed in controlled doses for valid medical reasons, which differentiates them from Schedule I drugs.