Which of the following best describes a Schedule I substance?

A Schedule I substance is defined as a drug that is illegal and has no accepted medical use in the United States. This classification indicates that these substances have a high potential for abuse and pose a significant risk of dependency. Consequently, they cannot be prescribed by healthcare providers or used in any medical contexts. Examples of Schedule I substances include heroin and LSD.

The other options describe characteristics of different schedules or categories of substances. For instance, options that suggest availability for pain management or prescription use pertain to substances that have accepted medical uses, typically classified under Schedule II or lower. Similarly, substances that are used in the treatment for addiction, such as certain medications for opioid dependence, do not fall under the Schedule I category, as they are recognized for legitimate medical applications. Therefore, the only choice that accurately captures the essence of a Schedule I substance is that it is illegal with no accepted medical use.