What is one of the common side effects of drugs containing codeine?

Drugs containing codeine are opioid analgesics that can significantly affect gastrointestinal motility. One of the well-documented side effects of opioids, including codeine, is constipation. This occurs because codeine and similar medications bind to opioid receptors in the gastrointestinal tract, leading to decreased peristalsis and slower transit time of stool through the intestines. As a result, individuals taking codeine may experience difficulty in having regular bowel movements, which is a common complaint when using these types of medications.

In contrast, dizziness can occur with codeine use but is not as universally associated or as significant as constipation. Severe headaches and heart palpitations are not typical side effects associated with codeine use. Hence, the most common and expected side effect from codeine is indeed constipation, making it the correct choice.