Which statement describes nicotine?

Nicotine is characterized as rapidly absorbed due to its ability to quickly enter the bloodstream when inhaled through cigarette smoke or other delivery systems. When nicotine is inhaled, it reaches the brain and achieves peak concentrations within a matter of seconds, which leads to near-instantaneous effects on behavior and mood. This swift absorption contributes to its addictive potential, as users seek the rapid onset of nicotine's effects.

The other characteristics do not accurately reflect how nicotine functions. For example, describing nicotine as a long-acting agonist would imply a prolonged duration of action, which is not the case since nicotine itself has a relatively short half-life. The notion of decreasing brain receptor activity contradicts its function as a stimulant, as nicotine actually enhances activity at nicotinic acetylcholine receptors, leading to increased neural transmission rather than a decrease. Lastly, while nicotine binds to receptors, it does not form persistent bonds; rather, it typically disassociates from the receptors, allowing for neurotransmission to resume. Therefore, "rapidly absorbed" is the most accurate description of nicotine's pharmacokinetic properties.