Which symptom is characterized by a feeling of sickness and may indicate hallucinogen use?

Nausea is a common symptom associated with hallucinogen use, particularly with substances such as LSD or psilocybin. Users may experience an upset stomach or a general feeling of sickness, which can occur due to the way these substances interact with the body's serotonin receptors and affect the gastrointestinal system. This symptom can be alarming and may lead to vomiting in some cases, making it a notable indicator of hallucinogen ingestion.

While other symptoms like piloerection, bloodshot eyes, and difficulty in speech can also be present with various drug uses or other medical conditions, they are not as specifically associated with hallucinogens as nausea is. Understanding the range of symptoms can help in recognizing potential substance use and providing appropriate assistance or intervention.