From the FDA Drug Label
Morphine causes miosis, even in total darkness. Miosis (small pupils) is caused by morphine, a full opioid agonist, as it affects the brain stem respiratory centers and other parts of the central nervous system 1.
- Opioid overdose can also lead to pinpoint pupils, but this is not a definitive sign as other conditions like pontine lesions may produce similar findings. Key factors to consider are the mechanism of action of morphine and its effects on the central nervous system.
From the Research
Miosis, or small pupils, is primarily caused by opioids, such as morphine and codeine, as well as other medications, substances, medical conditions, and normal physiological responses. The most significant factor contributing to miosis is the use of opioid medications, which can cause pupillary constriction as a direct effect of their mechanism of action on the nervous system 2, 3, 4. Other medications like cholinergic drugs and certain antipsychotics can also lead to miosis. Medical conditions such as Horner's syndrome, inflammation of the iris, brain injuries, and neurodegenerative diseases are additional causes. Physiologically, miosis occurs in response to bright light, near focus, and with aging. Toxins, including organophosphate pesticides and certain mushroom species, can also induce pupil constriction.
Key factors to consider in the diagnosis of miosis include:
- Medication use, particularly opioids
- Underlying medical conditions that may affect the nervous system or the eye
- Exposure to toxins or substances that can cause miosis
- Physiological responses to light and near focus
It's essential to understand the cause of miosis because it can serve as a diagnostic clue for underlying conditions, medication effects, or substance use, helping healthcare providers determine appropriate treatment approaches 5, 6. In clinical practice, identifying the cause of miosis is crucial for managing the underlying condition effectively and improving patient outcomes in terms of morbidity, mortality, and quality of life.