Nicotine

Tolerance 2

When large amounts of nicotine are present in the brain, the acetylcholine receptors become overstimulated.

This makes them temporarily insensitive, and acetylcholine and nicotine can no longer bind to them. Fewer signals are transmitted than usual, so more nicotine is needed to achieve the same pleasant feeling.

The neuron senses the lack of signals, and creates additional receptors for acetylcholine.