We recently updated the Ashwagandha page was updated to be much more expansive, currently residing at position 8 of our most cited pages (300+). We go back every year or so to revamp pages, and it was Ashwagandha's turn.
With the complete summary and the Ashwagandha page themselves being enough reading (both on Examine.com and through the cited sources) for any scientist out there, we are just going a recap on the most promising or at least most well talked about properties of this interesting herb:
Adaptogen-like effects: Ashwagandha is one of the primary adaptogen compounds (alongside rhodiola rosea and panax ginseng). If you want to reduce stress, consider them all viable options and then choose one of them based on safety or the other attributes of the herb.
Sedative/Anxiolytic: It seems that taking it in the morning or early afternoon can help sleep quality, and it's also non-sedating. Oddly, there are many anecdotes of ashwagandha making it hard to fall asleep if taken right before going to bed.
Physical Performance: Currently there are two studies showing increased VO2 max with this herb, and one of them is in elite athletes. Furthermore, a study in sedentary persons noted increased power output in the lower back and legs (no training required, but just a small boost in power) suggesting that Ashwagandha may be an ergogenic aid. Needs more evidence, but having something benefit the performance of elite athletes is indeed rare for supplements.
Social Anxiety: The sedative mechanism (enhancing GABA signalling without really acting like a benzodiazepine) is known to be anti-anxiety, but it is not very potent.
Anti-cancer: In short, Ashwagandha seems to enhance other anti-cancer agents including pharmaceuticals (but only has weak anti-cancer effects itself). The immune boosting properties may also be therapeutic, and (high doses) have been tested in women with breast cancer; improvements in quality of life, fatigue, and all functioning (social, emotional, and psychological) were found.
Immunity: Most of ashwagandha immunity benefits are because it reduces stress (by reducing cortisol).
Safety: It appears to be safe if used within the recommended dosing guidelines, although adequate drug-drug interaction testing has not been completed yet (kind of like Bacopa monnieri); it would be perfect if we just had this data).
It seems that ashwagandha has very promising pre-clinical evidence and pilot studies for its benefits, which mostly seem to anti-stress and anti-anxiety. Larger trials are definitely needed to confirm these benefits.