Which substance is primarily associated with symptoms such as tachycardia and hallucinations when used excessively?

Cocaine is primarily associated with symptoms such as tachycardia and hallucinations when used excessively due to its stimulant properties and its effect on the central nervous system. Cocaine increases levels of neurotransmitters like dopamine, leading to heightened energy, euphoria, and increased heart rate (tachycardia). In contrast, excessive use of heroin, an opioid, typically leads to symptoms such as respiratory depression, sedation, and decreased heart rate rather than tachycardia and hallucinations. Alcohol can also lead to hallucinations, particularly in withdrawal scenarios, but it is less directly associated with consistent tachycardia as compared to cocaine. Marijuana, while it can alter perception and mood, usually does not produce hallucinations or significant effects on heart rate in the same manner and scale as cocaine. Thus, cocaine's stimulatory effects make it the most likely candidate for causing these specific symptoms when consumed in excess.