Which sign is associated with hallucinogen intoxication?

Pupillary dilation is a classic sign associated with hallucinogen intoxication. Many hallucinogens, such as LSD and psilocybin, have a stimulating effect on the autonomic nervous system, which can lead to physiological responses like increased heart rate and blood pressure, as well as changes in the eyes. The dilation of pupils, also known as mydriasis, occurs as part of this autonomic response and is highly indicative of hallucinogenic substance use.

Other options relate to different effects and symptoms that may not be specifically associated with hallucinogens. For instance, muscle weakness is more commonly associated with depressants or certain medical conditions. Weight loss can occur due to a variety of factors but is not specifically linked with hallucinogen intoxication, which may lead to heightened sensory perception and appetite in some instances. Delirium is a state of mental confusion that can be caused by various substances, including intoxication from different classes of drugs, but it's not a defining characteristic of hallucinogen use. Thus, pupillary dilation stands out as a clear and direct sign of hallucinogen intoxication.