Most people actually consider milk thistle a pesky weed, and while it can be quite invasive, it also possesses remarkable medicinal benefits that make it worth keeping around. Most notably, this tall, thorny herb with spiky flowers has been prized for centuries for its anti-inflammatory, antioxidant and antiviral properties. It is also highly regarded as a liver tonic due to high amounts of a chemical compound known as silymarin.
Silymarin is a group of flavonoids (silibinin, silidianin and silicristin) known to help repair your liver cells when they've been damaged by toxic substances. These flavonoids also protect new liver cells from being destroyed by toxins. As such, milk thistle greatly improves the overall functioning of your liver, with specific applications related to cirrhosis of the liver, chronic liver inflammation and liver damage from alcohol and other intoxicating substances.
While all parts of the milk thistle plant are edible, silymarin is contained in the seeds only. Because a single plant produces thousands of seeds that spread very easily, you'd be wise to check with your local cooperative extension office to find out if milk thistle is considered an invasive species in your area. If it is, you may be banned from growing it.
Milk thistle (Silybum marianum) — also known as Mary thistle and holy thistle — is a common flowering herb1,2 within the Asteraceae family. Some of its close relatives include aster, daisy, dandelion, sunflower and ragweed. It is highly regarded for its anti-inflammatory, antioxidant and antiviral properties and has been used in traditional Chinese, European and Ayurvedic medicine for more than 2,000 years. It originated in Southern Europe, Asia Minor and the Mediterranean region, but now grows wild around the world.
Under almost any conditions, milk thistle grows 3 to 4 feet tall, featuring glossy, milky-white veined leaves and bright magenta or purple flowers beset with prickly spines. Its name results from the milky white sap its leaves release when they're crushed. Since its healing properties were first described in 40 A.D. by Greek physician and botanist Dioscorides, particularly related to treating snakebites,3 milk thistle has been used to treat a variety of ailments.
Today, milk thistle is available in a capsule, extract or powder form shown to benefit your liver, gallbladder, heart or prostate. According to the National Institutes of Health, silymarin is the most commonly used herbal supplement in the U.S. for liver problems.4 It is also useful as an essential oil.
Before you think about planting milk thistle in your garden or yard, be sure to check with your local cooperative extension to ensure it is not banned. Washington state5 recognizes the plant as a "Class A Noxious Weed" that must be eradicated when found. Although occasionally found in gardens, it is illegal to buy or sell milk thistle in Washington state.
Arkansas and Oregon also have restrictions. Even if you live elsewhere and are permitted to plant it, be forewarned: Milk thistle is a highly invasive weed that can quickly spread all over your yard, and neighboring yards as well. Milk thistle spreads quickly based on the reality a single flower head contains nearly 200 seeds.
Because these seeds germinate in temperatures ranging anywhere from 32 to 86 degrees F, this hardy plant can remain viable for nearly a decade. Once it is established and its seeds are allowed to spread, you will find it difficult, if not impossible, to stop it. Because milk thistle is also toxic to livestock, you will want to take care in planting it outdoors if you live on a farm or maintain farm animals of any kind.
Barring those concerns, you'll find milk thistle is easy to grow. It will tolerate any soil, and can get by even in drought conditions. Basically, you can plant them and leave them and they will still thrive. Below are steps you can take to plant milk thistle in your garden or yard:6,7
1. Choose a sunny or lightly shaded area
2. Direct sow milk thistle seeds in the spring after the last expected frost
3. Place seeds shallowly — at a depth of about a quarter of an inch — in groups of three to four seeds each
4. Space seed groupings about 30 to 36 inches apart
5. Water well to encourage growth (alternately, you can soak the seeds in water for 24 hours prior to planting them)
6. After seedlings appear, thin each group to the one strongest plant
7. Seeds will germinate in about three weeks in temperatures around 54 to 59 degrees F
When starting seedlings indoors, plant seeds about two months before the last frost. Fill starter pots with peat moss and follow the planting instructions above. Milk thistle seeds sown directly outdoors produce biennial plants in most climates, which means they will flower their second season. Plants started indoors are grown as annuals and will flower in the first year.
Milk thistle flowers attract pollinators such as bees and butterflies. In addition, many species of birds seek out the seeds for food. During late summer when the flowers dry out, it's common to see birds clinging to the spiny stalks of milk thistle and swaying in the wind as they chomp away on the seeds.
Given their many thorns, it is best to put on a pair of thick gardening gloves before attempting to touch milk thistle, especially when harvesting their flowers for seeds. Keep in mind the average milk thistle plant may possess upward of 6,000 seeds! About 90 percent of them will remain viable after harvest.8
If you plan to collect seeds, you will want to harvest them before the plants fully mature. If the plants mature unattended, the seed heads will break on their own, making seed harvesting impossible. This is because when milk thistle flowers begin to dry out (usually in the fall), they produce silvery-white, tufted seed heads known as pappus (similar to dandelions). To extract the seeds from the flower heads you will need to:9,10
- Cut dried blossoms off the plant from the base of the flower head
- Place the flower heads in a paper bag and keep the bag in a warm location for about a week to allow them to dry completely
- Put the dried flower heads into a burlap sack, shake the bag well and then use your hands to coax the remaining seeds from the heads
- Dump the seeds into a bucket and separate out the unwanted chaff
- Once all the chaff is removed, store your milk thistle seeds in an airtight container in a cool, dark place until you're ready to use them
Whether or not you are able to grow your own, high-quality, organic milk thistle is inexpensive and readily available at your local health food store. Under the direction of your doctor, you may want to consider adding milk thistle to your diet if you are dealing with a liver-based problem such as:11
- Nonalcoholic fatty liver disease
Additionally, animal studies involving silymarin suggest it is useful to reduce liver injury caused by a number of drugs and environmental toxins, including:12
- Acetaminophen (Tylenol)
- Alcohol, drugs and psychotropic medications
- Industrial chemicals such as carbon tetrachloride, toluene and xylene13
- Chemotherapy and radiation
- Iron overload
- Poisonous liquids such as phenylhydrazine
In case you are wondering how milk thistle can benefit you if you do not have liver issues, check out these seven additional ways milk thistle is purported to support your health:14,15
• Assists with antioxidant activity — Milk thistle seeds contain a potent antioxidant called silymarin, which helps your body fight free radicals and reduce inflammation
• Boosts prostate health — Silymarin and a related milk thistle compound called isosilybin B not only have been shown to support prostate health through normal cell development, but also to be effective in the treatment of prostate cancer.16
• Counteracts mushroom poisoning — Intravenous administration of silymarin is the only known remedy used to stabilize cell membranes and inhibit absorption of toxins from Amanita phalloides. This deadly mushroom, known as the death cap, is commonly mistaken for edible varieties.
• Encourages healthy skin — Due to its antioxidant properties, silymarin is believed to have protective effects on your skin. In lab research, it has exhibited preventive and anticancer effects against skin cancer.17
• Improves lipid profiles — Most likely due to the presences of silymarin, along with other flavonoids, milk thistle is thought to encourage proper lipid absorption and synthesis in your body. A 2012 study18 showed silymarin was effective to significantly reduced LDL ("bad") cholesterol and triglyceride levels, while significantly elevating HDL ("good") levels.
• Promotes normal blood sugar — Research suggests silymarin decreases fasting blood sugar levels. Authors of one such study said: "[S]ilymarin treatment in Type 2 diabetic patients … has a beneficial effect on improving the glycemic profile."19
• Supports your liver, kidneys and gallbladder — Milk thistle has long been known to support your liver, kidneys and gallbladder health. Silymarin helps your liver grow new cells by boosting protein synthesis, and it has been effective in addressing toxin-induced liver aliments, including the treatment of liver diseases and liver cancer.20 It protects your kidneys against inflammation, free radical damage and toxins. Silymarin has also been shown to prevent the formation of gallstones.21
Given its many health benefits, you may be interested in knowing how to use milk thistle. Below are some ways you can incorporate this unique herb into your diet:22
- Powdered — Use a mortar and pestle to crush milk thistle seeds into a powder that can be added to soups, stir-fries and other dishes
- Salads — Because the entire plant is edible, you can add milk thistle flowers, leaves, roots and stalks to salads or incorporate them into cooked dishes
- Smoothies — For a healthy liver smoothie,23 soak 2 tablespoons of milk thistle seeds in filtered water overnight; the next morning, add the milk thistle (and soaking water), 1 cup of lemon juice,1/3 cup of lycium berries and 1.5 cups of ice to your blender and combine until smooth
- Snacks — Although it may be a bit of an acquired taste, milk thistle seeds can be eaten dry, as is
- Tea — Crush either or both milk thistle seeds and dried leaves to make a loose tea blend you can steep in an infuser with hot water; add a healthy sweetener of your choice to tone down the somewhat bitter flavor, or add a peppermint teabag for a different taste sensation24
In addition to oral milk thistle supplements, you can also purchase it in essential oil form. Extracted from the ripe seeds, milk thistle oil is abundant in sterols, essential fatty acids, antioxidants and vitamin E, giving it nutritive and skin-protective properties.25 It may actually help soothe skin problems like acne, eczema and rosacea.26 Milk thistle oil is also commonly added to cosmetics. Here's one way you can use milk thistle oil on your hair:27
- Add one drop of milk thistle oil to 10 drops of your preferred carrier oil
- Massage the diluted oil all over your scalp 10 minutes before showering
- Wash and style your hair as usual
You can find milk thistle at most health food stores under the names silymarin or silybum. Your best options are extracts of milk thistle with silybum or silymarin standardized to 70 to 80 percent. The recommended daily intake is 420 milligrams in divided doses.28 While you can stay on milk thistle indefinitely, it is not generally recommended. Be sure to consult with your doctor before taking milk thistle on a continuing basis, especially if you are using other medications.
If you have concerns about your liver health or are interested in any of the other potential health benefits — anticancer, antidiabetic and heart-boosting properties — of silymarin, you may want to give milk thistle a try. If you are not able to grow it in your area, a high-quality milk thistle supplement may be worth considering. While milk thistle is the richest known source, you can also find silymarin in artichokes, turmeric and coriander (cilantro).
Despite its many beneficial properties, milk thistle is not for everyone. According to WebMD, you should not take milk thistle if any of the following conditions apply:29
- You experience bloating, diarrhea, gas, nausea or an upset stomach after taking it
- You are breastfeeding or pregnant
- You have a ragweed allergy
- You have cancer of the breast, uterus or ovaries, endometriosis or fibroid tumors (mainly because milk thistle can mimic the effects of estrogen)