From the Guidelines
No, narcotics typically cause pupil constriction (miosis), not dilation. Opioid medications like morphine, hydrocodone, oxycodone, fentanyl, and heroin bind to opioid receptors in the brain and stimulate the parasympathetic nervous system, which leads to constriction of the pupils 1. This pupillary constriction is often a clinical sign that healthcare providers look for when assessing for opioid use or overdose. In contrast, stimulants like cocaine, amphetamines, and MDMA typically cause pupil dilation (mydriasis). The degree of pupil constriction from narcotics can vary based on the specific drug, dosage, and individual response, but pinpoint pupils (extremely constricted pupils) are a classic sign of opioid intoxication.
Some medications, such as over-the-counter decongestants, cold and flu medications, allergy medications, and sleeping aids, as well as prescription psychoactive and motion-sickness medication, can cause pupil dilation due to their anticholinergic properties 1. However, narcotics are not typically associated with pupil dilation. In an overdose situation, the pupillary response, along with respiratory depression and decreased consciousness, forms part of the classic opioid toxidrome that medical professionals use for diagnosis.
Key points to consider:
- Narcotics cause pupil constriction, not dilation
- Opioid medications stimulate the parasympathetic nervous system, leading to pupillary constriction
- Stimulants, not narcotics, typically cause pupil dilation
- Pinpoint pupils are a classic sign of opioid intoxication
- Certain medications, not narcotics, can cause pupil dilation due to anticholinergic properties 1.
From the FDA Drug Label
Morphine causes miosis, even in total darkness. Pinpoint pupils are a sign of opioid overdose but are not pathognomonic (e.g., pontine lesions of hemorrhagic or ischemic origins may produce similar findings). Marked mydriasis rather than miosis may be seen due to hypoxia in overdose situations. Morphine causes miosis, even in total darkness, and little tolerance develops to this effect. Pinpoint pupils are a sign of opioid overdose but are not pathognomonic (e.g., pontine lesions of hemorrhagic or ischemic origins may produce similar findings). Marked mydriasis rather than miosis may be seen with worsening hypoxia in the setting of EMBEDA overdose Fentanyl depresses the respiratory centers, depresses the cough reflex, and constricts the pupils
Narcotics typically cause pupil constriction (miosis), not dilation. This effect is consistently described in the provided drug labels for morphine, heroin, and fentanyl 2, 3, and 4. While mydriasis (pupil dilation) may occur in certain situations, such as hypoxia in overdose, the primary and expected effect of narcotics on pupils is constriction.
From the Research
Narcotics and Pupil Dilation
- Narcotics do not typically cause pupil dilation. Instead, they cause pupillary constriction, also known as miosis 5, 6, 7, 8, 9.
- Studies have shown that opioids, such as morphine, heroin, codeine, oxycodone, oxymorphone, and hydrocodone, cause dose-related decreases in pupillary size 7.
- The pupillary effects of narcotics are affected by lighting intensity, with peak miosis detected under moderately dim interior lighting 5.
- Narcotics also affect the dynamic responses of the pupil, including the velocity of constriction to a light stimulus and the velocity of redilation after a light stimulus 7.
Mechanisms of Narcotic-Induced Miosis
- The mechanisms behind narcotic-induced miosis are not fully understood, but they are thought to involve the neural pathways responsible for regulating pupil size 6.
- The effects of narcotics on the pupil are species-specific and may involve the activation of opiate receptor subtypes 6.
- Tolerance to the pupillary effects of narcotics can develop with repeated administration 6.