What defines a "psychoactive substance"?

A psychoactive substance is defined as any substance that can induce a psychoactive effect when consumed. This means that it has the ability to affect the brain and alter an individual's mental state, perception, mood, or consciousness. Such effects can vary widely depending on the substance and the dose. This broad definition encompasses a wide range of substances, including legal medications, recreational drugs, and even certain foods or beverages that can change mental states.

The choice specifying that it always alters consciousness is limited, as not all psychoactive substances necessarily alter consciousness permanently or consistently; effects can vary among individuals. Medications prescribed by doctors can certainly be psychoactive, but not all psychoactive substances are medications, making the second choice too restrictive. The last choice incorrectly narrows the definition to only those substances that produce euphoria, while many psychoactive substances can have different effects, such as sedation, hallucination, or stimulation. Thus, the comprehensive nature of the correct answer aligns with the established understanding of psychoactive substances.