Final answer:
OTC cough medicines with codeine typically fall under Schedule III but are not commonly available over-the-counter in the U.S. due to their potential for abuse and serious side effects, especially in children.
Step-by-step explanation:
OTC cough medicines containing codeine are classified within the United States' controlled substance schedules. Specifically, OTC cough medicines with codeine generally fall under Schedule III of controlled substances. However, it is important to note that these medications are often not available over-the-counter in the U.S. and can vary by state law. They require a prescription due to risks of abuse and addiction associated with opioid medications.
Codeine is an opioid that has relatively low potency but still has abuse potential, like all opioids. Therefore, regulatory agencies have categorized it to help prevent misuse. Prescription opioid abuse has become a significant worldwide concern. This is particularly important in the case of cough medications for children, as the FDA has advised against the use of codeine-containing cough medication in this group due to the risk of serious breathing problems.
Despite being once viewed as the "gold standard" in cough suppressants, codeine's effectiveness has been questioned in recent clinical trials. There is evidence suggesting that it may not be more effective than a placebo, especially for acute cough in children. In addition, the adverse effects, such as the risk of overdose and serious side effects, have led to caution in prescribing these medications to younger populations.