The correct answer is serotonin.
Serotonin is a neurotransmitter (NT) produced in the human body. It is known as the "happiness" or "feel good" chemical. Many mood altering drugs and illicit substances like hallucinogens, antidepressants and stimulants interact with serotonin in the brain, which in turn alters people's moods, making them feel good and happy while consuming these substances.