Chestnut tree in bloom

The structure of the buds of horse chestnut (Aesculus hippocastanum) is described in an earlier OSMOSIS 17 (Spring 2000). Even at the bud stage, you can clearly see developing leaves and flowers and by mid-May to early June, horse chestnut trees are normally in full flower. It is a spectacular sight with many thousands of flowers in large pyramidal inflorescences; often known as ‘candles’.

KS2 and KS3 pupils can find plenty of interest exploring these flowers. Using their knowledge of flower structure and function they can investigate aspects of pollination, make some predictions, collect data and try to find reasons for some of their observations. Horse chestnut flowers show variation in the number of floral parts and also in the petal colour – the ‘blotches’ on the petals range from yellow through salmon pink to a pinkish-red (carmine). Many of the flowers function as ‘male only’ flowers – the female parts (gynoecium) remain undeveloped. (Pupils described these as ‘miserable looking’!)

At Juniper Hall Field Centre, we have used horse chestnut flowers as a basis for investigation with a number of groups of pupils. Some of the ideas which developed and data collected from two such groups are given here.

First pupils were given a single horse chestnut flower so that they could work out its structure. They noticed the variation in colour and tried to find reasons for this. One group suggested that the pinkish (red) flowers were older than the yellow ones. They had also noticed that when the flowers first open, the petal blotch was yellow and the stamens turned downwards, but as the flower developed, the stamens began to turn upwards and shed their pollen.

From these observations, the pupils predicted that ‘the red flowers will have fewer turned-down stamens than the yellow ones’. To test their prediction, they examined 144 flowers (5 to 10 for each pupil). In each flower, they recorded the number of stamens that turned up and the number turned down as well as the colour of the petal blotch. Because the number of stamens per flower varied, they decided to give numbers of stamens up or down as a percentage of the total number of stamens. Some individual results as well as combined class results are given in Tables 1 and 2.

Colour of blotches

Number of stamens



Salmon pink






Salmon pink






Salmon pink








Colour of blotches
Stamens ‘down’




Salmon pink




Table 2 Class results for 144 flowers were combined and the mean percentage of flowers with stamens down was calculated

Table 1 One pupil examined 10 flowers. In each flower she recorded the colour of blotches on the petals and whether the stamens were up or down. Here are her results. (She also calculated percentage ‘up’ and ‘down’ for each flower.)

They agreed that these results did give evidence to support their prediction. However, they also noticed that the turned down stamens in the red flowers appeared to have shed their pollen. This led to another follow-up study. A second group of pupils then predicted that ‘red flowers would have no pollen left’. To test this, they imitated a visit from a bee by pushing their little finger into different coloured flowers so that it touched the petal blotch. They then checked their finger to see if there was any pollen on it and always cleaned it before the next test. You can see in Table 3 that these results again supported the prediction. However, even though the data were less complex than that of the first group, the conclusions were not as clear-cut. Many red flowers have already shed all their pollen and very young yellow flowers have stamens that have not yet begun to shed pollen. There was also some difficulty in seeing pollen on fingers. To overcome this, some suggested using a cotton bud (home-made for economy, as a clean one is needed for each test).

Colour of blotches

Number of flowers
Total examined
Number with pollen
% with pollen



Salmon pink




Table 3 A different group of pupils tested the prediction that red flowers would have no pollen left. Here are their results

Of course there were limitations, but both these studies encouraged observation, led to collection of meaningful data and stimulated scientific thinking. They raised many interesting questions – leading to yet more ideas for investigations!

  • Does the number of red flowers per candle increase with time?
  • Do bees visit yellow flowers more often than red ones?
  • How long does it take for a single flower to change colour?
  • Is the change in colour affected by the length of time the flower has been exposed to sunlight? Or is some other factor involved, such as the beginning of the shedding of pollen or a visit by an insect?

It was encouraging to see how the pupils taking part in these activities became much more aware of the relationship between the structure, colour and movement of different floral parts as well as the behaviour of visiting insects. The pupils were also stimulated to take an interest in what happens to other flowers. We are grateful to staff and pupils from The Cavendish School (London NW1), and from Queensgate School (London SW7), who helped collect these data and for allowing us to publish their results in this article.

Anne Bebbington
(FSC, Juniper Hall, Surrey)

Useful references

Bebbington A (2000) Exploring a horse chestnut bud in OSMOSIS 17

Farrant P (1997) Colour in Nature Blandford, London

Hickey M, King C (1988) 100 Families of Flowering Plants CUP, 2nd edition

Proctor M, Yeo P, Lack A (1996) The Natural History of Pollination Harper Collins, London

Red horse-chestnut

Tree & Plant Care

More tolerant of dryness than horse-chestnut, but still grows best in a moist soil.
Red horse-chestnut has a taproot which may make planting difficult.

Disease, pests and problems

Large spiny fruits can be messy.
Leaf blotch and mildew are possible problems, but less so on this species than on related species.

Disease, pest and problem resistance

This hybrid is less susceptible to leaf blotch and mildew than European horse-chestnut.

Native geographic location and habitat

This is a hybrid cross between red buckeye (Aesculus pavia) and Common horse-chestnut (Aesculus hippocastanum).

Bark color and texture

Bark is gray-brown, becoming platy as the tree ages.

Leaf or needle arrangement, size, shape, and texture

Palmately compound leaves arranged in pairs (opposite).
Dark green with 5 or sometimes 7 leaflets.
Fall color is yellow-brown.

Flower arrangement, shape, and size

6 to 8 inch long, cone-shaped terminal cluster.
Flower color varies from pink to red.

Fruit, cone, nut, and seed descriptions

Shiny brown nuts in a 1 ½” prickly husk.
Horse-chestnuts are not true chestnuts and should not be eaten.

Cultivars and their differences

Fort McNair red horse-chestnut (Aesculus x carnea ‘Fort McNair’): 30 feet high and wide with a rounded form. Some resistance to leaf blotch. Pink flowers with yellow throats.

Ruby Red Horse-chestnut (Aesculus x carnea ‘Briotii’): 25 to 35 feet high and 25 to 35 feet wide with a compact, rounded shape. Deep red flowers with yellow throats.

The horse chestnut tree (Aesculus Hippocastanum) is currently in flower and we are all enjoying the candelabra display of delicate pink and white flowers. This old and prestigious tree, which provides both visual beauty and hands-on fun, is swamped with history, interesting facts and cultural references. Do you know where it got the name ‘Horse chestnut’ from, for example?

But, unfortunately, it’s not all good news for this forestry icon which is currently being plagued by two conditions.

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Horse chesnThis is everything you need to know about the horse chestnut tree…

1. The horse chestnut tree was first introduced to the UK from Turkey in the late 16th century. It is native to the Balkan peninsula.

2. The horse chestnut began its process of naturalisation in the UK after extensive planting by landscapers including Sir Christopher Wren – who planted a mile long pathway of the beautiful tree at Bushy Park, near Hampton Court.

3. Horse chestnut conkers are poisonous to most animals and will cause sickness if eaten.

4. The annual world conker championships have taken place in the village of Ashton, Northants, since 1965. The first ever game was played on the Isle of White in 1848.

5. Certain chemicals can be extracted from conkers to treat strains and bruises.

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6. The word ‘conker’ originally derived from the word ‘conch’ and the game was first played using snail shells.

7. The timber from horse chestnuts is a pale, creamy white and is light in weight and weak in strength, meaning it is not very sought after for commercial and carpentry purposes. It was, however, once used to make artificial limbs.

8. Horse chestnut trees can live for up to 300 years and, at their largest, can reach heights of 40 metres with 2 meter wide trunks.

9. The Aesculus Hippocastanum got its association with horses because, when the leaves fall, the stalks leave a scar on the twig which resembles the shape of a horseshoe complete with nail holes. The conkers also used to be ground and fed to horses as a remedy for coughs.

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On a more serious note, horse chestnuts are currently suffering from two conditions…

1. Leaf Miner Moth (Cameraria ohridella)

What is it?

Leaf miner moths spread their larvae over horse chestnut trees which burrow into the leaf tissue. Over time, this browns, dries and eventually kills the leaf. If the tree has a particularly bad infestation, the majority of the leaves could die.

There is no scientific evidence that leaf miner affect the health of the tree overall but it is thought to affect its annual calendar and knock events such as fruiting, leaf tint and leaf fall off schedule.

Where is it?

The larvae of these tiny moths were first observed in Macedonia in 1985 but were not discovered in the UK until 2002, in London.

The moths are currently spreading between 40 and 60km every year, which suggests that they may be being transported through the UK in vehicles.

What to do about it?

Forestry experts and researchers are currently still trying to assess the extent of leaf miner in the UK and are urging tree owners to record their horse chestnut’s health.

If you have spotted a new break out of leaf miner, record your update on the Forest Research website.

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2. Bleeding Canker

What is it?

This infection affects the trunk of the horse chestnut tree and can be identified by a brown, sticky substance oozing from the branches and bark of the tree.

The bacterial infection causing the tree to leak eventually splits the bark. As the years progress, the increased infection around the full diameter of the trunk will cause the tree to produce less, or premature, yellow leaves and, eventually, die.

Where is it?

Bleeding canker, or leaf tint, came to the UK in the 1970s and latest reports suggest that 49% of horse chestnut trees are now infected UK-wide.

What to do about it?

Unfortunately, because this disease is already so widespread, the Forestry Commission is not asking the public to closely monitor the trees. However, if you notice a tree in the early stages of infection, record it on the Forest Research website.

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Horse Chestnut

Contrary to popular belief, the horse chestnut is not a giant horse-sized nut, nor is it something that families roast over an open fire during traditional Christmas celebrations. The horse chestnut, in fact, describes the fruit of a broadleaf tree that can be found growing in Southeastern Europe. In herbal formulations, it goes through an extraction process and is standardized for use in various dietary supplements designed to support healthy veins, joints, muscles, and skin. Keep reading to learn more about the potential benefits and uses of the horse chestnut.

What is a Horse Chestnut?

The horse chestnut (Aesculus hippocastanum) or conker tree is a large deciduous tree native to the Balkan Peninsula that belongs to the Sapindaceae family, also known as the soapberry family. The horse chestnut tree prefers growing in moist, fertile, and well-drained soils in full sun to partial shade. Under ideal conditions, it can grow at a height of 50 to 75 feet, spreading its footprint from 40 to 65 feet and living for up to 300 years. That’s why the horse chestnut tree is commonly used for ornamental landscaping and for shade in parks, in village greens, along streets, and in large lawns. (1, 2)

When the tree is young, its bark is smooth and pinkish grey. However, the bark darkens and develops scaly plates as it ages. The horse chestnut tree blooms in mid-spring, around May, and features large palmate leaves with 5-7 pointed, serrated leaflets spreading from a central stem and conical clusters of white flowers of 4-5 fringed petals with a red, pink or yellow flush at the base. In dry conditions, the edges of the tree’s leaves may scorch and turn brown. (3)

The tree’s fruit is pollinated by insects and consists of large, globular, glossy mahogany brown seeds (Semen hippocastani), known as conkers in the UK, that are encased in spiky green husks, commonly referred to as the horse chestnut or buckeye. Each autumn, the prickly green seed pod turns brown and cracks, splitting open to reveal several hard, brown seeds inside. (4)

Once extracted from the husk, horse chestnut seeds look similar to the Ohio buckeye but are distinguished differently due to the sharp spines on their seed pods. (5) However, be careful not to confuse the horse chestnut (Aesculus hippocastanum) with the Ohio buckeye (Aesculus glabra) or the California buckeye ( Aesculus californica), as these are very different plants. In addition, keep in mind that the popular edible “sweet chestnut” (Castanea sativa and other Castanea), are in the Fagaceae (beech) family and produce edible nuts. The sweet chestnut is what families roast during traditional Christmas celebrations. Unlike the sweet chestnut, horse chestnuts and buckeyes (Aesculus) are in the Sapindaceae (soapberry) family and produce poisonous nuts that should never be consumed raw.

The horse chestnut tree’s seeds, bark, and leaves are used in herbal formulas for various health issues. Traditionally, the standardized extracts from the seeds of the horse chestnut tree have been used medicinally for the treatment of hemorrhoids, circulatory health, chronic venous insufficiency, varicose veins, rheumatism, bladder and gastrointestinal disorders, fever, and leg cramps. However, not all of these medical claims can be backed by science. (6) You will, however, find horse chestnut as an ingredient in a variety of dietary supplements, including capsules, tablets, liquid extracts, and tinctures, as well as topical ointments, and more. Continue reading to find out the science behind the horse chestnut.

How It Works

The unprocessed seeds, leaves, bark, and flowers of the horse chestnut tree contain a complex mixture of compounds that are believed to have certain medical qualities, including coumarins (esculin, aesculetin), coumarin glycoside (aesculin), and saponins (aescin), which are all believed to be bioactive, as well as flavonoids (quercetin, rutin, kaempferol), tannins (condensed & hydrolyzable), fatty acids, and sterols. (7, 8)

Aesculin, in particular, is poisonous and may increase the risk of bleeding. Aescin (or escin), on the other hand, is a different compound and is considered to be safe if taken in small amounts. Aescin is a mixture of triterpenoid and steroidal glycosides referred to collectively as saponins, is the main bioactive compound in horse chestnut that is responsible for most of its medicinal properties. According to the Department of Nutritional Sciences at the University of Toronto, “Saponins have been shown to have hypocholesterolemic, anti-coagulant, anticarcinogenic, hepatoprotective, hypoglycemic, immunomodulatory, neuroprotective, anti-inflammatory and antioxidant activity.” (9, 10)

Unfortunately, when ingested raw in an unprocessed form, the bioactive compounds in the horse chestnut may cause unwanted side effects such as severe gastroenteritis, also known as the stomach flu, an intestinal infection marked by diarrhea, cramps, nausea, vomiting, and fever. At its worst, ingesting unprocessed horse chestnut plant parts could also cause paralysis or coma. (11)

Ironically, the very same compounds that make the horse chestnut toxic are what make it potentially beneficial to human health, as well. When it is properly processed and standardized so that the active chemicals are separated out and concentrated, horse chestnut seed extract is considered safe for human consumption when used in low quantities and for short periods of time. (This process removes the poisonous aesculin.) However, even the processed extract could cause temporary itching, nausea, gastrointestinal upset, muscle spasms, or headaches. (12, 13)

Aescin is poorly absorbed by the body, at less than .25%, and the total flavonoids present amount to only 0.88% or 0.3%, which weakens the extract’s potential health benefits. Nevertheless, the horse chestnut is used in homeopathic medicine, because its bioactive compounds are believed to naturally thin the blood, help prevent fluid loss from veins, capillaries, and urine, and help prevent water retention (edema), among other potential health benefits. (14, 15)

A Brief History of Horse Chestnut

Horse chestnut was first cultivated in Turkey, part of the Balkan Peninsula. The origin of the horse chestnut tree’s name is unclear, but it is believed it comes from the mark left by the leaf stalk on the twig when it falls, resembling an inverted horseshoe with nail holes. Although eating raw horse chestnut is now understood to be a dangerous and possibly fatal mistake by humans, research indicates that historical uses included grinding up the fruit and feeding it to horses to relieve cough symptoms. (16)

Horse chestnuts were introduced to the UK in the late 16th century where it eventually became a popular element in the game of conkers (also known as Kingers). The first record of the game is from the Isle of Wight in 1848, modeled after a 15th century game played with hazelnuts. Conkers is still played today in Great Britain and Ireland. In fact, the World Conker Championships is held every year at Southwick, Northamptonshire. (17)

The game of conkers involves two players who each select one uncracked, firm, and symmetrical conker (horse chestnut seed) as a game piece. Each player punches a hole through the middle of their horse chestnut seed, threading a string about 25 cm long through the hole, tying a knot at one end, and letting the seed hang down from the string whose opposite end is tied around the player’s hand. The players then take turns at hitting their opponent’s seed. The first player draws the seed back for the strike, swinging it and trying to hit the opponent’s seed. The player gets three attempts for a clear strike. Extra attempts can be made if strings become tangled or if a strike causes the opponent’s horse chestnut seed to swing around in a full circle, known as ‘round the world. If the opponent drops their seed, the current player yells “Stamps” and jumps on it. The game continues until one of the horse chestnut seeds is destroyed. (18)

Historically, horse chestnut seed extract has been used for a variety of health conditions, including joint pain, gastrointestinal issues, fever, and leg cramps. Today, people take dietary supplements of horse chestnut seed extract to support health issues related to the function of veins and overall blood circulation. Common ailments involved in such supplement use include chronic venous insufficiency, varicose veins, hemorrhoids, and leg swelling after surgery. Sometimes, people also use preparations made from the bark of the horse chestnut tree to help support healing of skin sores. (19, 20)

Other uses for the horse chestnut include as an ingredient in shampoos and personal care products and as a starch substitute. In addition, due to the soft and smooth, fine texture of the horse chestnut tree’s bark, it is also a popular choice in wood carving projects.

Potential Benefits of Horse Chestnut

Usable parts of the horse chestnut tree for medical formulations include its seed, bark, and leaves. More specifically, horse chestnut seeds are used in herbal supplements to support vein health. Horse chestnut tree leaves and branch bark are used for skin care, and the leaves are also used for soft tissue health support and minor joint pain relief. However, most dietary supplements used to support optimal health are derived from its seed extracts. (21, 22)

Horse Chestnut Potential Health Benefits

  • Supports Vein Health
  • Supports Healthy Circulation
  • Supports Heart Health
  • Supports Joint and Muscle Function
  • Promotes Skin Healing

Horse chestnut seed extract has been clinically proven to help support overall vein health and promote healthy blood circulation throughout the body, which in turn may promote heart health, joints and muscle health, and healthy-looking skin. Most importantly, horse chestnut seed extract is used in a wide range of homeopathic treatments to support the health of people living with varicose veins (enlarged, twisted veins, usually found in your legs and feet, that appear pink or blue), chronic venous insufficiency (when the veins of the lower leg are unable to send blood back toward the heart), and hemorrhoids (swollen veins in the lowest part of your rectum and anus). (23, 24, 25, 26).

It is estimated that 25 percent of adults have varicose veins and similar circulatory issues, caused when blood doesn’t flow properly. Potential risk factors include obesity, a sedentary lifestyle, pregnancy, and old age. Varicose veins may cause painful discomfort or heaviness in the legs, as well as unattractive, visible gnarled veins that can be seen near the outer layer of the skin. Treatment may include lifestyle changes to improve circulation, such as losing weight, exercise, and using compression stockings. In addition, some people use dietary supplements such as those formulated with horse chestnut seed extract to help support healthy veins. (27)

Investigations in animal models suggest that horse chestnut seed extract, in particular, may have anti oedematous, venotonic, and anti-inflammatory properties. An anti oedematous is a substance that prevents or alleviates edema (fluid retention). (28) A venotonic is a substance that improves the tone of a vein by increasing the flexibility of elastic fibers in the vein wall. (29, 30) An anti-inflammatory helps prevent the body from releasing chemicals that increase the blood flow to an area of injury or infection, usually visible by redness and warmth, thereby preventing the body from damaging its own tissues. (31)

Several studies are examining the possible effect of horse chestnut seed extract supplements on people suffering from chronic venous insufficiency and varicose veins. Some reports suggest that it may help reduce edema, ankle and calf circumference, and symptoms related to chronic venous insufficiency and varicose veins. (32) According to research, “17 trials conducted on horse chestnut extract for the treatment of chronic venous insufficiency noted significant reductions in leg pain, edema, leg volume.” It was discovered that standard oral doses of a horse chestnut seed extract containing 50 mg aescin twice daily for 12 weeks appears to be effective in reducing symptoms of chronic venous insufficiency. (33) Another study reported that horse chestnut seed extracts standardized for escin are as effective as compression stockings. (34)

When it comes to supporting healthy blood circulation throughout the body, research suggests that horse chestnut seed extract supplementation may have a positive effect on not only the health of the veins in the arms and legs, but also blood circulation through the ears, skin, heart, and lower bowels. This is believed to be attributed to the ability of horse chestnut to naturally thin the blood and support circulation. The improved viscosity of the blood may help prevent possible clotting and blocking of veins, which has been known to be a major cause of stroke or heart problems. (35, 36) In studies on rats, aescin also appears to help enhance the effects of corticosteroids, reducing areas of inflammation. (37)

How to Buy Horse Chestnut

Warnings and Side Effects

When eaten in its raw, unprocessed form, horse chestnut is toxic to humans and most animals. (38) Although in the wild, horse chestnuts are eaten by deer, cattle, and horses, according to the American Society for the Prevention of Cruelty to Animals (ASPCA), horse chestnuts could cause severe vomiting, diarrhea, dilated pupils, convulsions, or coma. If you notice these signs in an animal such as a family pet, call an emergency veterinarian promptly. (39)

The bioactive compounds in horse chestnut seed extracts are poorly absorbed in the digestive tract, which means that they are flushed out through the kidney and gallbladder, causing much strain on the organs. (40) It is also believed that consuming large quantities of horse chestnut seed extract may lead to liver toxicity. (41) In addition, horse chestnut may trigger allergic reactions in some people. Also, due to the potential blood thinning and known circulatory properties of this plant, horse chestnut extract should not be taken with pharmaceutical blood thinners such as Warfarin and similar medications.

Other plants and trees that contain the same toxic chemicals contained within unprocessed, raw horse chestnut seeds, leaves, flowers, and bark are the white hawthorn tree (Crataegus oxyacantha), the ash tree (Fraxinus), and the sweet bursaria (Bursaria spinosa). So be careful when you’re trying new botanical-based supplements! Always do your research first. (42)

Dosage Recommendations

Do not use unprocessed raw horse chestnut preparations, as they can be toxic and lethal when ingested, as indicated above. Horse chestnut seed extracts that have been processed properly to reduce the risk of toxicity may be given orally through dietary supplementation in various forms or applied topically to support healthy circulation and wound healing.

When searching for dietary supplements containing processed horse chestnut for safe consumption, look for trusted brands. If you’re interested in trying a horse chestnut supplement, shop the Natural Healthy Concepts store. All products sold through Natural Healthy Concepts have been pre-vetted for safe, quality ingredients and manufacturing processes. (43)

It’s recommended that you keep your supplemental dosage of horse chestnut between 400 – 600 mg daily, not to exceed standardization for aescin at 100 – 150 mg daily. Doses should be separated by 12 hours (one dose for morning and one for night). (44)

As with all supplements, always consult with your healthcare provider first before trying a new supplement in your daily health routine. Adhere to the instructions on the nutritional label of the product you are using for exact dosage recommendations. It is generally recommended that children, pregnant women, people with allergies, or those taking certain blood thinning medications DO NOT take horse chestnut supplements.

If you’re looking for vein and circulatory health support, try a processed horse chestnut seed extract-based supplement today! It may make a difference to your health.


Horse Chestnut


  • Horse chestnut trees are native to the Balkan Peninsula (which includes such countries as Albania, Bulgaria, Greece, Romania, and Serbia), but are grown worldwide.
  • Historically, horse chestnut seed extract was used for joint pain, bladder and gastrointestinal problems, fever, and leg cramps.
  • Today, people use horse chestnut extract as a dietary supplement for chronic venous insufficiency (when the veins of the lower leg are unable to send blood back toward the heart), hemorrhoids, and swelling after surgery. Preparations made from the tree’s bark are applied to skin sores.
  • Usable parts of the plant include the seed, bark, and leaf, but seed extracts are most common.

How Much Do We Know?

  • There have been some studies in people on horse chestnut for chronic venous insufficiency but very little research has been done for other conditions.

What Have We Learned?

  • A 2012 systematic review of 17 studies published between 1976 and 2002 suggested that horse chestnut seed extract can improve leg pain, swelling, and itching in people with chronic venous insufficiency when taken for a short time. Results from one of these studies suggested that horse chestnut seed extract may be as effective as wearing compression stockings.
  • Preliminary evidence from one Chinese study suggested that escin, the main ingredient in horse chestnut, may help restore fertility in some men. However, since all the men in the study also received other supplements and drugs, it’s unclear whether the improvement was due to this compound alone or the combination approach.

What Do We Know About Safety?

  • The unprocessed seeds, leaves, bark, and flowers of horse chestnut contain esculin, which is poisonous and may increase the risk of bleeding. (Escin, on the other hand, is a different compound and is considered to be safe.)
  • Properly processing horse chestnut seed extract removes esculin. The processed extract is considered generally safe when used for short periods of time. However, the extract can cause some side effects, including itching, nausea, gastrointestinal upset, muscle spasm, or headache.

Keep in Mind

  • Tell all your health care providers about any complementary or integrative health approaches you use. Give them a full picture of what you do to manage your health. This will help ensure coordinated and safe care.

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