The antidote+ is made by mixing a toadflax and a yew root in a vial of coconut milk, giving 155 Herblore experience. The potion requires level 68 Herblore. Four doses are created instead of the usual three.
The Antidote+ cures poison, and provides a longer immunity than super antipoisons. This potion reduces poison damage by 100% for 9 minutes.
It is very useful at many boss places such as Dagannoth Kings to increase the amount of time you can remain there.
However, it is often recommended to use an Antidote++ as it is often cheaper, and about 40% more effective.