FES Quintessentials (Research) Vervain 7.5ml FES is continually researching the healing properties of a wide array of wildflowers from California and beyond. The Vervain essence is currently being studied. However feedback from practitioners who use it in everyday practice have found it may be useful for the following: Encourages the positive potential of serenity, wisdom and tolerance. Remain enthusiastic towards the world around you while not imposing your views on others.