Which drug is known as a powerful mydriatic and can take up to two weeks to wear off?

The drug known as a powerful mydriatic that can take up to two weeks to wear off is Atropine. Atropine works by blocking the action of acetylcholine on the iris sphincter muscle, leading to dilation of the pupil (mydriasis) and paralysis of the ciliary muscle, which impairs accommodation.

Atropine has a long duration of action compared to other mydriatics, with its effects potentially lasting up to two weeks, especially in pediatric patients. This prolonged effect is due to the drug's high potency and its ability to strongly bind to muscarinic receptors, resulting in extended pupil dilation.

In contrast, other drugs listed, like Cyclopentolate and Tropicamide, have much shorter durations of action, typically lasting from a few hours to a day. Phenylephrine, while effective as a mydriatic, is primarily a sympathetic agonist that also has a shorter duration of pupil dilation compared to Atropine. Thus, Atropine is distinguished by its prolonged effect, making it suitable for specific diagnostic and therapeutic scenarios.