Vervain is a digestive stimulant widely used in traditional medicine in North America.
Bitter herbs are thought to stimulate digestive function by increasing saliva production and promoting both stomach acid and digestive enzyme production. As a result, they are particularly used when there is low stomach acid but not in heartburn (where too much stomach acid could initially exacerbate the situation). These herbs literally taste bitter. Some examples of bitter herbs include greater celandine, wormwood, gentian,dandelion, blessed thistle, yarrow, devil's claw, bitter orange, bitter melon, juniper, andrographis, prickly ash, and centaury.. Bitters are generally taken either by mixing 1–3 ml tincture into water and sipping slowly 10–30 minutes before eating, or by making tea, which is also sipped slowly before eating.
Some bitters widely used in traditional medicine in North America include yarrow, yellow dock, goldenseal, Oregon grape, and vervain. Oregon grape's European cousin barberry has also traditionally been used as a bitter. Animal studies indicate that yarrow, barberry, and Oregon grape, in addition to stimulating digestion like other bitters, may relieve spasms in the intestinal tract.