Which of the following substances is a Schedule II controlled substance?

Dihydrocodeine with codeine is classified as a Schedule II controlled substance due to its potential for abuse and dependence. Schedule II drugs are substances that have a high potential for abuse, which may lead to severe psychological or physical dependence. Dihydrocodeine, in combination with codeine, falls into this category because both components are opioids known for their analgesic properties and associated risks of misuse.

In contrast, phenobarbital is classified as a Schedule IV controlled substance, which indicates a lower potential for abuse compared to Schedule II drugs. Chlordiazepoxide, also a Schedule IV substance, belongs to the benzodiazepine class, which is recognized for its abuse potential but is placed in a lower schedule than Schedule II. Tramadol is classified as a Schedule IV substance as well, as it is considered to have a lower potential for abuse compared to drugs in Schedule II, despite its pain-relieving properties.

Thus, understanding the classifications of these substances is crucial for recognizing the legal restrictions and prescribing regulations that apply to each drug, particularly in a pharmacy practice setting.