For 50 years, Seratonin has been regarded as the brain’s primary ‘happy hormone’ or, to put it more accurately, neurotransmitter. In addition, treatment for depression has commonly been spearheaded by drugs like Prozac, which increase serotonin’s availability in the brain. This type of medication, known as SSRI drugs (which stands for selective serotonin re-uptake inhibitors), works by preventing serotonin from leaving the synapses in the brain. The more serotonin, the better the mood.