Dopamine is a neurotransmitter (i.e. chemical) in the brain that gives us great feeling. From here:
Dopamine plays a role in how we feel pleasure. It's a big part of our unique human ability to think and plan. It helps us strive, focus, and find things interesting.
Is there any chemical(s) released in the brain that have an opposite effect to dopamine, that is, some chemical that makes us feel bad?