This effect is temporary, and will not kill a player unless an additional source of damage is dealt to them. This is because the effect pauses when a player's health reaches . If the character regains health while the poison effect is still active, their health will continue to deplete until it once again reaches .
Like all status effects, it can be removed by drinking Milk.
Sources of Poison
A variant of the poison effect (called Fatal Poison), is exclusive to Minecraft: Bedrock Edition. This effect will continue to deduct health from a player, even after they reach , which kills the player.