Yes. I know they are neurotransmitters.
Serotonin and Dopamine.
Actually those are just normal neurotransmitter substances.
But reread what Tom said:
Some substances change the level of serotonin and dopamine. This can produce feelings of euphoria and hallucinations.
Some are chemical addictions, as in the changes in serotine (spelling?) and dophine (spelling?) others
People become addicted to these substances, and also become dependent on the effect they give.