Final answer:
The characteristic symptom of someone on a hallucinogenic drug is enhanced sensory perception and vivid hallucinations.
Step-by-step explanation:
The symptom characteristic of someone on a hallucinogenic drug is C. Enhanced sensory perception and vivid hallucinations. Hallucinogens such as LSD, mescaline, and psilocybin lead to profound alterations in sensory and perceptual experiences. Users may experience a range of sensory and physical effects, including:
- Seeing or hearing things in a distorted way or perceiving things that do not exist (hallucinations).
- Intensified feelings and sensory experiences such as brighter colors or sharper sounds.
- Mixed senses, such as "seeing" sounds or "hearing" colors.
- A skewed perception of the passage of time, with time seemingly going by slowly.
While increased energy and heart rate are also physical effects of hallucinogens, the most distinctive symptoms of hallucinogen use are related to changes in sensory perception and the experience of hallucinations.