St. John's wort is one of the world's best known medicinal herbs. It really might be better classified as a medicinal weed. This plant invades lawns and gardens and fields , spreading by sending out an extensive network of rhizomes and also by seed. Even though it probably originated in the Near East (Turkey and Greece to Iran), it has spread all over the world as a pest. It is called a "wort" because of its huge root system, making it hard to pull up. The term "St. John's wort" actually applies to an entire genus (group) of plants. The plant with the medicinal efficacy is just one kind of St. John's work, Hypericum perforatum.
The top of third of the plant is used to make herbal medicines. You could use the plant as a dried herb or to make tea, but most of its desired effects depend on a plant chemical called hypericin, so it's best to use a standardized product in capsules. You'll need 900 mg of hypercin a day to get the effect you seek, whether it's relieving depression or taking it as a natural sleep aid. And there is a special situation in which St. John's wort is a very good insomnia treatment.
St. John's Wort Is Especially Useful for Relieving Sleep Problems in Menopause
For women going through menopause, St. John's wort is among the best of all herbs as natural sleep aids. One of the most common of all menopause symptoms is poor sleep. And one of the reasons so many women going through menopause have sleep problems is hot flashes. Estrogen replacement therapy is the most common prescription for hot flashes , although its very serious downside is that it increases the risk of vaginal bleeding , recurrences of estrogen receptor positive cancers of the breast  and cancers of the uterus , and also increases the risk of pulmonary embolism, heart attack, and stroke .
There are many herbal, natural sleep aids for hot flashes. Some don't really work. Soy, ginseng, and kava kava, for example, have other benefits, but they won't usually help either sleep problems of hot flashes . Flaxseed oil really is more useful for treating vaginal dryness , although some women find that it helps with hot flashes.
Vitex (also known as vitex agnus-castus) is a popular herbal natural sleep aid for hot flashes, although it can take a few months to start to work Red clover has significant benefit for both hot flashes and vaginal dryness, but it won't help a lot if there issues beyond just estrogen levels. 
St. John's wort helps with hot flashes and insomnia in women going through menopause in ways that other herbs can't. Its actions aren't primarily hormonal. It relieves inflammation, and it acts on an enzyme in the brain called monoamine oxidase (MAO). This helps it relieve depression. The herb also relieves anger, palpitations, creeping sensation, mood swings, and muscle pain, and it fights mild viral infections. All of these actions together make St. John's wort an herb of choice for women whose needs for chronic insomnia treatment arise from menopause. 
What Do Women Need to Know About Taking St. John's Wort?
There are two things that every user of St. John's wort needs to know. First of all, you need to take enough. It just doesn't work if you aren't taking the equivalent of 900 mg of hypercin (this information will be on the label) every day. There are many products that don't contain the amount you really need . If you take this dose, you will begin to feel the results in about three weeks.
The other thing people who take St. John's wort need to know is that there is a really long list of medications with which it interferes. St.John's wort is best used in a "purely natural" approach to chronic insomnia treatment. St. John's wort reduces the effectiveness of:
- Antiretroviral drugs,
- Benzodiazepine tranquilizers,
- Estrogen and progestin oral contraceptives (the Pill),
- Heart rhythm drugs such as amiodarone and mexiletene,
- High blood pressure drugs of the beta-blocker (for instance, metoprolol) and calcium channel blocker (for instance, amlopidine or verapamil) classes,
- Immune suppressers (especially tacrolimus, which is used on cardiovascular stents), and
- Statin drugs for cholesterol.
It's also just not a good idea to take St. John's wort if you are taking any prescription drug for depression, even for four weeks after you quit taking that drug. Prescription antidepressants, opioids, cocaine, DMT, LSD, MDMA, migraine medications, and Parkinson's drugs combined with St. John's wort can trigger serotonin syndrome, a condition of dangerously high blood pressure, severe headaches, and mania that can take several days to several weeks to pass. Use St. John's wort on its own for gentle relief of insomnia and other symptoms of menopause.
What if you aren't a woman going through menopause? St. John's wort isn't just a useful natural sleep aid. It also may be helpful for mild to moderate depression, but only if it is used alone. Don't use it with other antidepressant drugs or herbs or any of the medications listed above.