Slowed A5E

A slowed creature's Speed is halved.
A slowed creature takes a −2 penalty to AC and Dexterity saving throws.
A slowed creature cannot take reactions.
On its turn, a slowed creature can take either an action or a bonus action, not both. In addition, it can't make more than one melee or ranged attack during its turn.

Source: Adventurer's Guide (EN Publishing) · License: Creative Commons Attribution 4.0 / OPEN GAME LICENSE Version 1.0a details