Final answer:
Benzodiazepines can cause anterograde amnesia, impairing the formation of new memories for up to 6 hours from the onset of their effects, which helps in reducing anxiety.
Step-by-step explanation:
Benzodiazepines, such as alprazolam (Xanax), diazepam (Valium), and lorazepam (Ativan), are central nervous system depressants prescribed mainly for their anti-anxiety, sedative, and anticonvulsant effects. One of the significant effects of benzodiazepines, which can last for up to 6 hours from the onset of the drug's action, is anterograde amnesia; this is a condition where the formation of new memories is impaired, which can significantly reduce the anxiety associated with distressing procedures or events. Benzodiazepines are also known for their muscle relaxation and hypnotic properties but are not commonly used for pain relief, which is more often associated with opioids. Therefore, the correct answer to the student's question is C. anterograde amnesia.