Short answer: NIH says kava may help anxiety but not generalized anxiety disorder, and some ashwagandha preparations may help stress and insomnia.12 Both have rare liver injury reports; kava's led to an FDA advisory in 2002 citing transplants.3 Neither should be mixed with sedatives. We found no trial comparing them.
| Kava | Ashwagandha | |
|---|---|---|
| Plant | Pepper-family plant from the South Pacific1 | Withania somnifera, an evergreen shrub2 |
| What NIH says | May help anxiety after several weeks; does not appear to help generalized anxiety disorder1 | Some preparations may help insomnia and stress; anxiety evidence unclear2 |
| Liver | Rare injury, some serious or fatal; FDA advisory cited over 25 reports abroad and 4 transplants13 | Rare cases of liver injury2 |
| Other side effects | Stomach upset, headache, dizziness; skin changes with long, heavy use1 | Drowsiness, stomach upset, diarrhea, vomiting2 |
| Do not combine with | Sedatives such as benzodiazepines, or alcohol1 | Caution with sedatives, thyroid, diabetes, blood pressure, seizure and immune-suppressing medicines2 |
| Pregnancy | May carry special risks1 | Avoid; do not use while breastfeeding2 |
Kava: NIH says there has been a fair amount of research on anxiety. Kava supplements may help but may need several weeks to work, and kava does not appear to help generalized anxiety disorder.1
Ashwagandha: NIH says many small trials used different preparations; some may help insomnia and stress, the anxiety evidence is unclear, and it may be safe for up to 3 months.2
We found no trial that compared them directly.
In 2002 FDA warned that kava supplements may be linked to severe liver injury, citing hepatitis, cirrhosis and liver failure in over 25 reports in other countries, four of them needing liver transplants, and a previously healthy young woman in the US who needed a transplant.3 NCCIH notes cases have also involved kava drinks made with water.1 For ashwagandha, NCCIH describes rare liver injury cases and advises against it with autoimmune or thyroid disorders and before surgery.2
See a doctor for yellow skin or eyes or brown urine.3 More detail: Ashwagandha vs rhodiola: how do the two herbs compare?, and the Kava and Ashwagandha guides.