**Core Concept**
Pupillary dilatation, also known as mydriasis, is a condition characterized by the enlargement of the pupil. This can occur due to various pharmacological or physiological factors, including the use of certain substances. In the context of drug abuse, pupillary dilatation can be a significant indicator of specific substance use.

**Why the Correct Answer is Right**
Pupillary dilatation is commonly associated with the use of anticholinergic substances, such as cocaine. Cocaine acts by blocking the action of acetylcholine at muscarinic receptors in the eye, leading to a decrease in parasympathetic tone and subsequent mydriasis. This effect is due to the blockade of the muscarinic M3 receptors on the radial muscles of the iris, which normally constrict the pupil.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not directly relate to the cause of pupillary dilatation. The substance mentioned does not have a well-documented effect on the pupil size.
**Option B:** This option is incorrect because it is not commonly associated with mydriasis. While some substances may have multiple effects, this particular effect is not characteristic of this substance.
**Option C:** This option is incorrect because it does not directly relate to the cause of pupillary dilatation. The substance mentioned does not have a well-documented effect on the pupil size.

**Clinical Pearl / High-Yield Fact**
When assessing a patient with suspected substance abuse, it is essential to consider the effects of various substances on the pupils. A dilated pupil can be a critical indicator of cocaine use, and this information can aid in the diagnosis and management of the patient.

**Correct Answer: C. Cocaine**