Darsurion

The leaves of this plant, which a novice will surely confuse with nettles, are the basis of a preparation prized by the barbarians.
Drinking a darsurion maceration increases the duration of a barbarian's rage by 1 round if this one is triggered within 10 minutes of drinking the brew. Its effects are cumulative if you drink more than one potion, with a maximum of 5 additional rounds, meaning 30 seconds.