'Most people think of dopamine as the pleasure neurotransmitter. Dopamine is a major regulator of the reward pathway, which involves pleasure, but it doesn’t directly influence the sensory or mental experience of pleasure. Dopamine is a wanting chemical. It compels us to seek, to do, to move. Ultimately, dopamine triggers reward pathways as a way to motivate the organism to do the things that improve fitness, survival, and genetic proliferation. That it’s most active in the parts of the human brain that control movement and higher order thinking illustrates this fact nicely.'
You can read how internet use affects dopamine and people's behaviour and what you can do about it here.