Final answer:
A drug overdose is most likely to result in unequal pupils, as certain drugs can cause one pupil to constrict or dilate more than the other.
Step-by-step explanation:
Unequal pupils, also known as anisocoria, refers to a condition in which one pupil is larger or smaller than the other. Among the given options, a drug overdose is the most likely condition to result in unequal pupils. Certain drugs, such as opioids or sympathomimetic agents, can cause one pupil to constrict or dilate more than the other.
For example, opioids like heroin can cause pinpoint pupils (miosis), while sympathomimetic agents like cocaine can cause pupils to dilate (mydriasis).
Therefore, option A, Drug overdose, is the correct answer.