It totally depends on the aspects of psychology you study. Some theories in psychology are just that, theories. They don't have scientific backing. However, reputable evidence from studies into neurotransmitters in the brain has been very beneficial for developing treatments for depression, for example. Psychology is quite closely linked with biology, however as I already stated, it depends on what you actually study.
People who have no idea what the subject entails and assume it's about society and nothing more are simply wrong. People are looked at on an individual basis and as part of society, not one or the other. There are so many unanswered questions so it would be silly to leave out certain methods considered "non-scientific" if they are the most effective for that particular research.
If all you studied were social aspects of psychology, it is a social science. If you concentrated on biological and cognitive psychology, it would be a science.