**Core Concept**
A "bad trip" refers to a severe, distressing psychological reaction during psychedelic drug use, characterized by intense hallucinations, paranoia, panic, and disorientation. This phenomenon is most strongly associated with **lysergic acid diethylamide (LSD)**, a potent serotonergic hallucinogen that acts primarily on 5-HT2A receptors.

**Why the Correct Answer is Right**
LSD binds with high affinity to 5-HT2A receptors in the cortex, leading to profound alterations in perception, mood, and cognition. This receptor activation disrupts normal neural communication, resulting in vivid hallucinations, emotional instability, and anxiety—hallmarks of a "bad trip." Unlike cannabis, which can cause anxiety but rarely leads to full-blown psychotic episodes, LSD is more likely to induce acute, severe psychological distress, especially in vulnerable individuals or under stressful conditions.

**Why Each Wrong Option is Incorrect**
Option A: Cannabis can cause anxiety or paranoia, but it does not typically produce the intense, unpredictable, and often terrifying hallucinations seen in a "bad trip." The risk of severe adverse reactions is significantly lower.
Option C: "None" is incorrect because both cannabis and LSD can cause adverse reactions, but LSD is the most strongly associated with classic "bad trip" symptoms.
Option D: While both drugs can cause psychological disturbances, only LSD is classically and clinically defined as causing a "bad trip" in psychiatric literature.

**Clinical Pearl / High-Yield Fact**
LSD is the most well-documented cause of a "bad trip" in psychiatric practice. Patients may experience acute psychosis, derealization, and autonomic hyperactivity—especially if they have a history of mental illness or use the drug in a non-therapeutic setting.

✓ Correct Answer: B. LSD