Which of the following is NOT a characteristic of hallucinogens?

Hallucinogens are a class of drugs known for their significant effects on perception, mood, and cognitive processes. The primary characteristics of hallucinogens include the distortion of perceptions and the evocation of sensory images that may not be present in the environment. These substances can trigger vivid visual or auditory hallucinations and alter the user's sense of reality.

The characteristic that is not typically associated with hallucinogens is the exciting of neural activity specifically in the sense of speeding up brain functions or increasing arousal. Instead, hallucinogens often lead to altered states of consciousness without necessarily inducing high levels of neural excitation; they can cause profound changes in thoughts and perceptions rather than simply increasing energy levels or alertness.

Absent sensory input refers to the way hallucinogens can create experiences or sensations in the absence of real external stimuli. This can include visual or auditory experiences that feel real to the user but are not actually occurring. Thus, while hallucinogens indeed distort perceptions and evoke sensory images, they do not operate primarily by exciting neural activity in the traditional sense that many stimulants do.