From webMD: "Ashwagandha contains chemicals that might help calm the brain, reduce swelling, lower blood pressure, and alter the immune system. Since ashwagandha is traditionally used as an adaptogen, it is used for many conditions related to stress. Adaptogens are believed to help the body resist physical and mental stress."

It makes me sleepy so I only take at night now.

Another source with linked articles: this site won't let me post links. The below is from an article in Medical News Today about the health benefits of ashwagandha.

Stress and anxiety
Ashwagandha may have a calming effect on anxiety symptoms when compared with the drug lorazepam, a sedative and anxiety medication.

A 2000 study suggested that the herb had a comparable anxiety-reducing effect with lorazepam, suggesting that ashwagandha might be as effective for reducing anxiety. However, the researchers conducted this study in mice, not humans.

In a 2019 studyTrusted Source in humans, researchers found that taking a daily dose of 240 milligrams (mg) of ashwagandha significantly reduced people’s stress levels when compared with a placebo. This included reduced levels of cortisol, which is a stress hormone.

In another 2019 studyTrusted Source in humans, taking 250 mg or 600 mg of ashwagandha per day resulted in lower self-reported stress levels, as well as lower cortisol levels.

Although this research is promising, scientists need to collect much more data before recommending the herb to treat anxiety.