The endocrine system is closely connected with the brain, so our mood largely depends on the level of different hormones in the blood. Each of us knows this on our own. By the hormones of happiness, not hormones are usually meant, but one of the neurotransmitters - the substances that are responsible for transmitting the signal from one nerve cell to another. Dozens of different mediators work in the brain, including endorphins, dopamine and serotonin. All of them were discovered in the middle of the 20th century. Each of them was dubbed "the hormone of happiness": it was noticed that they are associated with a sense of pleasure. The level of these compounds increases when something pleasant happens (or is expected), and decreases during a period of depression or apathy.
However, the more neuroscientists study these substances, the more difficult is their connection with a particular emotion. And the more obvious is the inability to model chemical happiness.