Choose the one word substitution for the following description: A drug which makes a person see things that are not really there.

Introduction / Context:
One word substitution questions check whether you know precise technical terms for detailed descriptions. In this case, the description refers to a special type of drug that affects perception and causes a person to experience sights or sensations that are not actually present. Such drugs are discussed in medicine, psychology, and social studies.

Given Data / Assumptions:
- Description: A drug which makes one see things that are not really there. - Options: Aphrodisiac, Steroid, Carcinogen, Hallucinogen. - The key idea is creating false perceptions or hallucinations.

Concept / Approach:
A hallucinogen is a psychoactive drug that causes hallucinations, which are false sensory experiences such as seeing, hearing, or feeling things that do not exist in reality. The other options refer to very different types of substances with different effects. By focusing on the idea of seeing things that are not there, we can identify hallucinogen as the correct term.

Step-by-Step Solution:
Step 1: Identify the key phrase in the description: see things that are not really there. Step 2: Recall the definition of a hallucination: a perception without external stimulus. Step 3: Recognise that a hallucinogen is a drug that produces hallucinations. Step 4: Check each option: - Aphrodisiac is a substance believed to increase sexual desire. - Steroid is a class of organic compounds, often used medically or for building muscle. - Carcinogen is a substance that can cause cancer. - Hallucinogen specifically refers to drugs like LSD that cause hallucinations. Step 5: Only hallucinogen matches the description given in the question.

Verification / Alternative check:
Think of common examples. Substances such as LSD or certain mushrooms are known as hallucinogens because they cause users to see patterns, colours, or beings that are not actually present. In contrast, steroids are associated with hormone like effects, carcinogens with causing cancer, and aphrodisiacs with arousal. None of these categories are defined by causing visual illusions or hallucinations.

Why Other Options Are Wrong:
Aphrodisiac affects desire, not perception, and therefore does not fit the description. Steroid covers substances often used for medical treatment or performance enhancement but does not necessarily produce hallucinations. Carcinogen is dangerous because it may lead to cancer, not because it alters what a person sees or hears.

Common Pitfalls:
A common mistake is to confuse technical scientific terms that sound similar or are frequently mentioned in health discussions. Candidates might choose carcinogen simply because it seems serious, without matching it to the given description. To avoid this, always focus on the specific effect described: seeing things that are not really there points directly to hallucinations and therefore to hallucinogens.

Final Answer:
The correct one word substitution is Hallucinogen.