Hedonism can be conjoined with psychological egoism – the theory that humans are motivated only by their self interest – to make psychological hedonism: a purely descriptive claim which states that agents naturally seek pleasure. Hedonism can also be combined with ethical egoism – the claim that individuals should seek their own good – to make ethical hedonism the claim that we should act so as to produce our own pleasure.
However, hedonism is not necessarily related to egoism. The Utilitarianism of John Stuart Mill is sometimes classified as a type of hedonism, as it judges the morality of actions by their consequent contributions to the greater good and happiness of all. Note that this is altruistic hedonism. Whereas some hedonistic doctrines propose doing whatever makes an individual happiest (over the long run), Mill promotes actions which make everyone happy. Compare individualism and collectivism.
It is true that Epicurus recommends for us to pursue our own pleasure, but he never suggests we should live a selfish life which impedes others from getting to that same objective. Some of Sigmund Freud’s theories of human motivation have been called psychological hedonism; his “life instinct” is essentially the observation that people will pursue pleasure. However, he introduces extra complexities with various other mechanisms, such as the “death instinct”. The death instinct, Thanatos, can be equated to the desire for silence and peace, for calm and darkness, which causes them another form of happiness. It is also a death instinct, thus it can also be the desire for death. The fact that he leaves out the instinct to survive as a primary motivator, and that his hypotheses are notoriously invalidated by objective testing, casts doubt on this theory.