There are easily hundreds of "traditional herbal remedies" out there, and they run a wide range from "actually useful medicinally" to the equivalent of using the grass on your front lawn to cure a common cold. Many of them are ascribed near-mystical status because of their use through the ages.
The Science of Herbal Remedies
Look, we live in a capitalist society that strives to extract every bit of value it can get out of anything it can. On the one hand, any traditional remedy is likely to be studied extensively and any actual value in it will be processed, isolated, and turned into a synthetic medicine with much higher potency than the herb itself. On the other hand, there are a limited number of scientists studying traditional remedies, and there are hundreds of different plants and herbs that might have some medicinal use.
It's difficult to dismiss herbal remedies entirely. The idea that capitalism will have isolated and extracted every bit of value from them already relies on ignoring one fact about medical history: modern doctors and scientists tend to discount anything older than a few decades as uninformed.
Just because the remedy was used back when miasma theory was the norm and no one quite understood that things could be microscopic, doesn't mean it's nonsense!
Take the idea of a plague doctor. Plague doctors dressed in funny masks and robes to treat people with the plague. The masks they wore didn't really have filtration in them, but they were stuffed with herbs that served a similar purpose. They might not have known that germs could transfer sickness, but they knew that using gloves and full-body protective robes kept them safer. A lot of the basics of modern PPE are present in a plague doctor outfit. Even though the basic science was wrong, the results were not.
This idea repeats itself throughout history. Those ancient people knew a thing or two, even if they didn't have the knowledge or equipment to understand why what they knew was effective.
That's why we concern ourselves with herbal remedies in the 21st century. Just because an herb was used to treat a lot of things it can't actually treat doesn't mean it doesn't have health benefits at all.
All About Ashwagandha
Ashwagandha is, as you might be able to guess, an herbal remedy. It is common in Ayurvedic medicine, that is, traditional medicine originating in India and the surrounding areas.
The plant itself is a small shrub that only grows to be 14-20 inches tall. It grows naturally in the drier regions of India, Nepal, Yemen, and China, in dry, stony soil and partial shade.
The plant itself is known by several names. Ashwagandha is just one of those. It is also known as Indian Ginseng, poison gooseberry, and winter cherry. The scientific name is Withania Somnifera. "Withania" is thought to come from a British scientist Henry Witham, who studied fossil botany. Somnifera means "sleep-inducing" because of the observed effect that the plant has some level of sedative effect. The Indian name Ashwagandha comes from two words in Sanskrit; "ashva" meaning "horse" and "gandha" meaning "smell", referring to the way the root smells.
Incidentally, the name "Indian ginseng" comes from the fact that many of the chemicals isolated within the plant -- phytochemicals like withanolides, steroidal lactones, and over 40 others – are structurally similar to Panax Ginseng.
Traditional Medicine Uses
Ashwagandha has been used throughout history as an herbal remedy to treat a variety of ailments. The use of the herb has been traced as far back as 6,000 BC, making it one of the oldest traditional remedies out there today. It has been used as a "Rasayana", which is a concept in Ayurvedic medicine simply meaning "life-extending". 
In more modern terms, Ashwagandha has been used as:
- A tonic: a medicine meant to give energy and a feeling of vigor and well-being.
- An aphrodisiac: a medicine meant to enhance sexual performance and libido.
- A narcotic: a medicine meant to boost the mood.
- A diuretic: a medicine meant to enhance the passing of urine.
- An anthelmintic: a medicine meant to kill parasitic worms.
- An astringent: a medicine meant to constrict or shrink tissues and reduce swelling.
- A thermogenic: a medicine meant to boost the body's energy consumption.
- A stimulant: a medicine meant to boost energy production.
In other words, it has been used to generally enhance health, treat wounds, increase sexual performance, and so on. All of these are pretty typical uses of traditional medicine, boosting energy levels, making one feel healthier, and treating common ailments.
As far as specific ailments, well, you can throw pretty much anything at the wall and most of it will stick. It has been used to boost the health of frail children, treat infirmity caused by age, help with constipation and rheumatism, treat nervous breakdowns, and more.
Modern Medical Uses
Ashwagandha has been studied extensively, but many of the studies performed and written up about it are poor-quality. Good quality scientific experiments require control groups, large sample sizes, and careful selection for relevant traits. Many studies on Ashwagandha do not have these qualities and are thus of questionable quality. That said, some do exist, and they indicate that the Indian root may have some real health benefits.
Ashwagandha may help reduce blood sugar. Diabetes is one of the most common ailments globally, so anything that may help treat it is something worth looking into. Studies like this one have suggested that an Ashwagandha supplement may have the effect of reducing blood sugar levels by increasing insulin production and improving insulin sensitivity in muscle tissues. In other words, it makes your body produce more of the chemical that processes blood sugar and opens up your cells to process that sugar more readily. This has the added effect of boosting energy because burning sugar as fuel is how your body gets much of its energy.
Incidentally, this is an example of a study that wasn't well conducted. It tested a mere six people, which is not a viable sample size, and it did not have a control group to compare the effects. Even though it's on the trusted source of PubMed, it's not a high-quality or reliable study. Always check into the studies people cite to prove their points!
Ashwagandha might have anti-cancer properties. We will not tell you that Ashwagandha cures cancer (because it doesn't). There are zero human studies that show any results whatsoever. There are, however, several promising animal studies that show that chemicals in the herb might help disrupt cancer cell processes, as well as making them less resistant to apoptosis, or programmed death. Animal studies, primarily in mice, saw that large concentrations of Ashwagandha might help with the treatment of breast, lung, colon, ovarian, and brain cancers. Again, though, no such evidence exists for humans, so do NOT try to take this supplement as a replacement for cancer therapy.
Ashwagandha might help reduce stress levels. In your body, when you are stressed, you produce cortisol. Cortisol is a hormone that is produced in the adrenal glands and released in the body when you're stressed, as well as when your blood sugar is too low. Cortisol encourages your body to store sugar as fat, among other things. Essentially, it prepares your body to survive through times of stress, which in early history when we were evolving typically meant times of lower food availability and higher energy expenditure. 
Ashwagandha has been shown in some studies to help reduce bodily cortisol levels. Reducing the level of cortisol in your body helps calm you down and makes you less susceptible to stress and stress-related ailments.
Ashwagandha might help reduce anxiety. Anxiety and stress are highly interlinked, so anything that helps with one is likely to help with the other. Indeed, Ashwagandha is primarily known in the west as a treatment for anxiety. Several studies, such as this one, this one, and this one, have all shown that an extract of Ashwagandha phytochemicals helped reduce stress levels and the related effects of anxiety and insomnia.
Ashwagandha might help reduce depression. One thing you might notice in modern medicine is that most medications meant to treat anxiety are also antidepressants. This is because the bodily mechanisms behind anxiety and depression are very similar, and often stem from the same sources. People with anxiety typically have depression, and vice versa, though it's not always in the same level or even noticeable compared to the other.
As a side effect of several studies into anxiety, some study participants note the reduction in the effects of depression. This hasn't been studied as a primary effect, and thus the results aren't well-backed by science, but it's possible that this supplement has some antidepressant effects.
Ashwagandha may boost testosterone and fertility in men. Some studies like this one have been performed on the aphrodisiac effects of the root, primarily in men. This study looked at a number of infertile men, and revealed that their seminal plasma indicated both increased sperm count and increased motility, which translates to increased fertility. Additionally, some evidence exists that suggests the root can increase testosterone levels in men. While this isn't one of the primary advertised effects of the root these days, it may have some promising chemicals worth looking into.
Side Effects and Warnings
One of the problems with herbal medicine is that plants are, well, plants. Plants grow in a variety of uncontrolled environments, and they pick up chemicals and impurities from the soil, water, and air around them. The quality, purity, and efficacy of the plants can vary from year to year, from location to location, and even from plant to plant.
One of the benefits of modern medicine is the ability to study and isolate specific chemicals that have a tangible effect on the body, then study those for their effects and side effects. Herbal remedies can be studied, but, well, there's a lot going on. As mentioned above, Ashwagandha has well over 40 different phytochemicals in it. Even if some of them are hugely beneficial, if others are detrimental, using the plant itself might not be a good idea.
General studies indicate that Ashwagandha is safe enough in small doses, but there are two major warnings you want to be aware of.
First of all, Ashwagandha might interfere with pregnancy. Some of the phytochemicals might cause uterine contractions or toxicity that causes miscarriage. Avoid taking it if you're pregnant or trying to become pregnant.
Second, because Ashwagandha might help reduce blood pressure and blood sugar, it can interact with medications that do the same. This can result in either making those medications less effective or making them too effective. Going from hyperglycemia to hypoglycemia is a bad thing, and medication doses are typically calculated to bring you into a specific range, which the herbal supplement might push you past.
There's also some evidence that shows Ashwagandha makes the immune system more active, which can trigger or exacerbate the effects of autoimmune diseases like lupus, rheumatoid arthritis, and psoriasis. It's best to avoid this herbal remedy when you're taking any of the drugs listed in the "interactions" section of this page, and talk to your doctor about it if you're using it and they're prescribing you medication.
It's possible that there are some tangible health benefits of Ashwagandha, for anxiety, depression, diabetes, and other bodily diseases. True proof, and the isolation of the relevant chemical for use in clinical settings, still needs to be studied.
