How does ADH act as a vasoconstrictor

My understanding is that it allows for water reabsorption in the collecting duct of the kidney. I know this increases blood pressure, but how exactly does it act as a vasoconstrictor?

If you understand that it increases blood pressure, then you should know why it works as a vasoconstrictor.

What happens is that it causes reuptake of sodium, which promotes the reuptake of water in the collecting duct. This will increase your blood volume, which greatly lowers your blood pressure. Now to counteract this decrease in arteriole blood pressure, your arteries will then vasoconstrict to increase peripheral resistance and cause an increase in blood pressure.