Serotonin, also known as 5-hydroxytryptamine, is a monoamine, neurotransmitter, and hormone that plays an important role in the body (5-HT). It is released from several different areas dispersed throughout the body. The serotonergic system encompasses the entire central nervous system (CNS) as well as the gastrointestinal tract (GI). The vast majority of serotonin is found outside of the central nervous system (CNS), where it can exert its influence on a wide variety of physiological processes. On the other hand, the two per cent of serotonin that is found in the central nervous system plays a critical part in the genesis of a wide variety of mental disorders. In the central nervous system, serotonin is responsible for modulating a wide variety of processes. Some of these functions include anxiety, learning, memory, the processing of rewards, and sleep. Serotonin exerts its effects via its receptors. Serotonin and serotonin receptors are significant in a variety of mental and neurological problems, including brain functions and the serotoninergic system. People experience contentment and peace of mind when serotonin is active. Humans show symptoms of despair, anxiety, and impulsive aggression when serotonin is inactive or at low levels. Early alterations in serotonergic signalling have been associated with a variety of neurodevelopmental conditions, including depression, aggression, and impulsiveness, as well as neurodevelopmental disorders such as schizophrenia, autism spectrum disorder, obsessive-compulsive disorder, and attention deficit hyperactivity disorder. The purpose of this review is to examine in depth how serotonin levels influence psychopathological conditions such as aggression, impulsivity, depression, etc., as well as its function in neurodevelopmental disorders.