Which symptom is commonly associated with heroin use, affecting the parasympathetic nervous system?

The symptom associated with heroin use that affects the parasympathetic nervous system is constipation. Heroin, as an opioid, binds to specific receptors in the brain and body, leading to a slowing of gut motility. This occurs because opioids can inhibit the action of nerves that stimulate peristalsis, the process that moves food through the digestive tract. As a result, individuals using heroin often experience constipation, which is a well-documented side effect of opioid use due to its impact on the gastrointestinal system.

In contrast, increased heart rate is typically associated with stimulants rather than opioids. Insomnia can occur in various contexts of substance use but is more related to withdrawal symptoms or concurrent substance use rather than a direct effect of heroin itself. Enhanced reflexes are typically not a symptom associated with heroin use; instead, opioids tend to depress the central nervous system, leading to slower reaction times. Thus, the choice of constipation aligns accurately with the physiological effects of heroin on the parasympathetic nervous system.