Opioid intoxication: This is the most common cause of bilateral pinpoint pupils due to the opioid's effect on the parasympathetic nervous system, leading to pupillary constriction.

Pontine stroke: A stroke affecting the pons in the brainstem can cause damage to the pupillary constriction centers, leading to pinpoint pupils.
Pilocarpine or other cholinergic toxicity: Medications or substances that stimulate the parasympathetic nervous system can cause pupillary constriction.
Horner's syndrome: Although typically unilateral, bilateral Horner's syndrome can occur due to various causes, including stroke, tumor, or trauma, affecting the sympathetic pathways.

Subarachnoid hemorrhage: Although pupillary dilation is more common in subarachnoid hemorrhage due to third nerve compression, some cases can present with pinpoint pupils, especially if there is increased intracranial pressure affecting the brainstem.
Status epilepticus: Prolonged seizure activity can lead to various neurological signs, including alterations in pupillary size.
Brainstem encephalitis: Inflammation of the brainstem can affect pupillary reflexes, among other neurological functions.

Argyll Robertson pupils: A condition characterized by bilateral small pupils that constrict when focusing on a near object but do not react to light, often associated with neurosyphilis.
Holmes-Adie syndrome: A rare neurological disorder affecting the autonomic nervous system, which can cause a tonic pupil that reacts poorly to light but constricts with near focus.
Familial amyloid polyneuropathy: A genetic disorder that can lead to autonomic dysfunction, including pupillary abnormalities.