He taught that there is no un-caused cause; there is nothing that comes from nothing.
This is getting into semantics, but one could perhaps say that the atoms themselves are the uncaused causes.
Cicero In his De Finibus says this;
Quote"The swerving [of the atoms] is itself an arbitrary fiction; for Epicurus says the atoms swerve without a cause, — yet this is the capital offence in a natural philosopher, to speak of something taking place uncaused."
However, the atoms are uncaused if we are speaking in terms only of their existence. The particular motion of the atoms is partially caused by an infinite regress of other causes (an endless chain of billiard balls bouncing, hooking, clinging, separating, and hurling apart through the void inertially), and partially, as in the swerve, their motion is caused by their own nature.