It genuinely depends which aspect of it you study, and how deep you study it. I wouldn't say that AS/A2 is a science, but certainly aspects of degree level are, understanding the specific workings of the brain, neurotransmitters, how each area works and what can affect it, how different drugs can affect you..
When most people think of psychology, they think of social psychology and nothing else, which is why people think it's what I like to call "airy fairy". They completely ignore the in depth study of mental illness, biological psychology, not to mention the workings of lab equipment etc.