Psychological thriller is a thriller story which emphasizes the abnormal psychological states of its characters. In terms of classification, the category is a subgenre of the broader ranging thriller category, with similarities to Gothic and detective fiction in the sense of sometimes having a “dissolving sense of reality”, moral ambiguity, and complex and tortured relationships between obsessive and pathological characters. Psychological thrillers often incorporate elements of and overlap with mystery, drama, action, slasher and horror (particularly psychological horror). They are usually books or films. – Wikipedia
Action and psychological aspects both are used to add to the suspense.
With a psychological thriller the conflict (battle!) is through the mind, skills, and wit of main characters, reversing the more normal thriller “plot over character” expectations ie. a psychological thriller reader needs to understand the character, character can (sometimes) be slightly more important than plot (although I prefer both in equal measures).
Characters shouldn’t win using physical talents or efforts, but rather using their mind, wits or smarts.
Elements of drama, mystery and horror can often find themselves in the psychological thriller due to the emphasis on motivation and the mind.
There are Life and death situations and certainly at the end (climax) but this could well involve death or danger to themind or intrinsic identity or values of the hero rather than a physical threat.
Psychological thrillers often deal with common themes such as death, reality, perception, identity, existence or purpose, and one or two of these themes should be wound through the novel.
Motives and intentions are more important than technical aspects of how a crime is done.
Readers expect the story to focus around both the hero and the villain, via changes in point of view and scenes involving each separately.