 The development of 5-HT2C receptor knockout mice in the mid-1990s was a hallmark achievement in the identification and development of serotonergic drugs for weight loss.These knockout mice were hyperphagic, which led to obesity, partial Leptin resistance, increased adipose deposition, insulin resistance, and impaired glucose tolerance.As a result of these symptoms, the researchers identified a functional role for the receptors in serotonergic regulation of food intake and body weight.