Aloe vera

What is aloe?

Aloe (often called aloe vera) produces two substances - gel and latex - which are used for medicinal purposes. Aloe gel is a clear, gel-like substance found in the inner part of the leaves of the aloe plant. Aloe latex is found directly under the skin of the plant and is yellow in color. Some aloe products are made from the whole shredded leaf and therefore contain gel and latex.

Aloe medicines can be taken orally or applied to the skin. Aloe gel is taken orally for osteoarthritis, intestinal disorders such as ulcerative colitis, fever, itching and inflammation and as a general tonic. It is also used for stomach ulcers, diabetes, asthma and to treat the side effects of radiation therapy. However, most people use aloe gel to apply to the skin as a remedy for skin problems such as burns, sunburns, chilblains, psoriasis and cold sores. There is some scientific research to support such applications. Some chemicals contained in aloe gel may be effective in accelerating wound healing. However, it is too early to consider this proven, as scientific studies have come to contradictory conclusions. One study even suggests that aloe gel may delay wound healing. Some people take aloe latex orally, usually for constipation. Less commonly, aloe latex is taken orally for epilepsy, asthma, colds, bleeding, missed periods, colitis, depression, diabetes, multiple sclerosis, hemorrhoids, varicose veins, bursitis, osteoarthritis and glaucoma or other vision problems. However, oral ingestion of aloe latex is unlikely to be considered safe and harmless. There are concerns that some of the chemicals found in aloe latex may cause cancer. In addition to this, aloe latex puts a strain on the kidneys and can lead to serious kidney disease or even death. Until a few years ago, aloe latex was an ingredient in many laxatives. However, as long-term use of such preparations leads to a kind of habituation effect and more and more had to be used to achieve the desired laxative effect and the manufacturers were unable to provide any data on safety, such laxatives were withdrawn from the market in some countries.

Dosage forms of aloe vera

Aloe vera gel: Aloe vera gel can be applied to the skin to reduce inflammation, nourish the skin and heal wounds (2).
Aloe vera juice and capsules: Aloe vera can be taken orally via supplements to relieve constipation, boost immune function and reduce diabetes symptoms (1).

Ingredients of aloe vera

Aloe vera leaves consist of three layers (1, 3, 4):

Bark (outer layer) - The bark protects the plant, transports substances such as water and starch, and produces proteins and carbohydrates.
Latex (middle layer) - This layer contains glycosides (sugars bound to other compounds). Barbaloin/aloin, isobarbaloin and emodin are the primary active compounds.
Gel (inside the leaves) - The gel contains water, sugars, amino acids and vitamins. Glucomannan, salicylic acid and phytosterols are the primary active ingredients.

Latex and gel contain most of the active ingredients. The vitamins and anthraquinones contained in aloe vera have antioxidant properties. The enzymes, glycoproteins, fatty acids and hormones it contains have an anti-inflammatory effect (1).

How does aloe work?

As already mentioned, the usable parts of the aloe plant are the gel and latex. The gel may cause changes in the skin that could help with conditions such as psoriasis. Aloe appears to be able to promote wound healing by improving blood flow to the wound area and preventing the death of cells around the wound. In addition, aloe gel appears to have properties that are harmful to certain bacteria and fungi.

Aloe latex contains chemicals that have a laxative effect.

Possible health benefits of aloe vera

Aloe vera can promote the healing of burns and other wounds

Aloe vera is often used to treat burns due to its soothing, moisturizing and cooling properties. In 3 studies involving 80 patients with burns, aloe vera helped treat these wounds better than two antibacterial ointments (nitrofurazone and silver sulphadiazine). The aloe gel was also better than the two ointments at speeding up the regrowth of new skin and relieving pain. Aloe gel was also effective in 12 patients who had undergone skin grafting (5, 6, 7, 8). In another study of 18 patients with facial scarring, aloe gel helped speed up the healing of the skin. The treatment also reduced wound pain better than an antibacterial ointment. In another study of 60 people suffering from anal fissures, aloe vera juice powder helped to accelerate wound healing and reduce pain and bleeding (9, 10). Aloe vera gel also helped with chronic wounds in 2 studies involving 137 subjects. It was at least as effective as two medicinal gels (phenytoin and betamethasone) (11, 12). In addition, aloe vera accelerated the healing of surgical wounds. It was effective in two clinical trials involving 80 women who had undergone cesarean section and 49 subjects recovering from hemorrhoid removal (13, 14). However, there are conflicting results from other studies. In a study of 21 women with surgical scars, applied aloe vera gel significantly slowed wound healing compared to a standard ointment (15). The ingredients glucomannan (sugar) and gibberellin (a plant growth hormone) contained in aloe vera interact with growth factors, which can stimulate the activity and growth of skin cells. In this way, aloe vera applied to the skin could stimulate collagen formation and wound healing (1). In addition to this, aloe vera improved collagen composition, which helps wounds to heal faster (16). All this evidence suggests that aloe vera may accelerate wound healing.

Aloe vera could promote skin health

In a study of 30 participants with dry hands, aloe vera (by wearing a glove for 8 hours a day) improved dry skin within 4 days. After 10 days, significant improvements in skin thickness, wrinkling and redness were observed. In another study, an aloe vera gel applied to the skin improved the moisture of the skin on the forearms of 20 female volunteers (17, 18). In a study of 41 patients with psoriasis, an aloe vera gel reduced redness, scaling and pain by 72.5%. In this study, however, the placebo was even more effective in reducing the symptoms of psoriasis (82.5%). Another aloe vera gel was more effective than a corticosteroid (triamcinolone acetonide) applied to the skin in a clinical trial involving 80 subjects with mild to moderate psoriasis (19, 20). In a small clinical study of 25 people, an aloe vera gel together with other ingredients was effective in improving the condition of seborrheic dermatitis (21). Aloe vera gel applied to the skin of rats increased the production of metallothionein, an antioxidant protein. This protein prevents oxidative damage caused by UV radiation, prevents suppression of antioxidants and reduces the release of immunosuppressive cytokines (IL-10) (22). Sugars contained in aloe vera may help to improve skin hydration by stimulating skin cells. The increase in collagen and elastin could make the skin softer and more elastic and reduce wrinkles (17, 1). Although the scientific evidence is limited, the available research suggests that aloe vera may help to increase skin hydration, relieve inflammatory skin conditions and reduce oxidative damage to the skin.

Aloe vera could relieve acne

Aloe vera products could help relieve acne. Acne products with aloe vera may be less irritating to the skin than traditional acne treatments. A small 2014 study found that a cream containing a combination of conventional acne medicine and aloe vera gel was more effective than the acne medication or a placebo in treating mild to moderate acne (55). In this study, lower levels of inflammation and fewer lesions were observed in the group that used the cream with aloe vera over an 8-week period.

Aloe vera could help with diabetes

In a clinical trial involving 30 patients with type 2 diabetes and high cholesterol levels, supplementation with aloe vera gel capsules helped to control diabetes. Taking 300 mg of aloe vera gel in capsule form twice daily for two months lowered blood glucose levels, total cholesterol levels and LDL (bad) cholesterol levels. It also reduced HBA1c, which is a measure of long-term blood glucose levels (23). In another clinical trial involving 45 subjects at increased risk of type 2 diabetes, two aloe vera leaf gel products were also able to reduce blood glucose levels, insulin levels and cholesterol levels (total cholesterol and LDL cholesterol). In another study of 136 obese, pre-diabetic subjects, an aloe vera gel complex reduced body weight and insulin resistance (24, 25). A meta-analysis of 9 studies found that diabetics showed the greatest improvements in blood glucose levels after taking aloe vera compared to healthy subjects (26). In human cells, an aloe vera compound (aloe-emodin glycosides) increased glucose uptake and glycogen synthesis. This may help to lower blood glucose levels and reduce insulin resistance (27). A limited number of studies suggest that oral aloe vera may help lower blood glucose and lipid levels in people with type 2 diabetes. Despite these promising studies, existing diabetes medication should never be replaced in whole or in part by aloe vera supplementation without consulting the treating physician.

Aloe vera could promote the healing of mouth ulcers

In a study of 40 patients with lip ulcers, aloe vera gel reduced the healing time. It also reduced pain and wound size (28). In another study of 90 patients, aloe vera gel completely healed 75% of mouth ulcers. It was particularly effective in reducing ulcer size, redness and weeping of the ulcers (29). In a clinical study of 26 patients suffering from throat cancer, a mouthwash containing aloe vera was as effective as anti-inflammatory benzydamine in relieving mouth ulcers resulting from radiation therapy. However, another study of 58 subjects concluded that aloe vera gel was ineffective. This could be related to the low cumulative radiation levels, as aloe vera gel was only effective at high radiation doses in another study (30, 31, 32). In summary, the results for the treatment of lip ulcers are promising, while the results for radiation-induced ulcers were mixed. Further research is needed before the use of aloe vera can be recommended in these areas.

Aloe vera could promote oral health

Aloe vera toothpaste and mouthwashes are natural options for improving oral hygiene and reducing plaque.

Results from a 2017 study show that subjects who used an aloe vera toothpaste showed significant improvement in their oral health (56). This study included 40 adolescents who were divided into two groups. One group used an aloe vera toothpaste twice a day, while the other used a traditional toothpaste containing triclosan. After 30 days, the aloe vera toothpaste was found to be more effective than the triclosan toothpaste in reducing yeast infections, plaque and gingivitis. The subjects who used the aloe vera toothpaste showed better overall oral health with no side effects observed.

Aloe vera has anti-inflammatory effects

In a study of 40 volunteers, an aloe vera gel reduced UV-induced inflammation when applied to the back. Aloe vera gel was more effective than a hydrocortisone cream in reducing inflammation and skin redness (33). In mice, aloe vera gel applied to the ears reduced inflammation caused by an irritant compound (34).

In human intestinal cells, aloe vera gel reduced inflammation in a dose-dependent manner. This suggests that aloe vera may have the potential to treat inflammatory bowel disease (35). Aloe vera gel was also able to reduce inflammatory markers in human immune cells (36). The anti-inflammatory effects of aloe vera stem from its ability to reduce PGE2 production and stop the cyclooxygenase pathway (1). In addition to this, aloe vera suppresses other inflammatory markers such as TNF-alpha and IL.1B (37). It contains C-glucosyl chromium, an anti-inflammatory compound (38).

Aloe vera could have antimicrobial properties

In a clinical trial involving 390 volunteers, an aloe vera mouthwash was as effective as antibacterial chemicals in removing plaque. After 30 days, the aloe vera group also had healthier gums and less plaque compared to the control group (39). Herpes simplex is a virus that can cause cold sores and other oral conditions. Aloe vera gel killed the herpes simplex virus without damaging other cells (40). In addition, aloin extracted from aloe vera deactivated several types of viruses (influenza, herpes simplex and varicella zoster) (41). Water- and alcohol-based Aloe vera extracts inhibited Gram-positive and Gram-negative bacteria, with the alcohol-based extract being more effective. The extracts inhibited Enterococcus bovis, Staphylococcus aureus, E. coli, Proteus vulgaris, P. mirabilis, Pseudomonas aeruginosa, Morganella morganii and Klebsiella pneumoniae in the test tube (42). Purified aloe vera protein also inhibited the growth of fungi (Candida paraprilosis, C. krusei and C. albicans) (43). Aloe vera contains antimicrobial compounds (phenols, salicylic acid, lipol, urea, nitrogen and cinnamic acid) that inhibit viruses, bacteria and fungi (1). Aloe vera breaks up bacterial cells and stops their growth (44). Although these results are promising, further research is needed as only one human study has investigated the antimicrobial effects of aloe vera.

Aloe vera could promote digestive health

Consuming aloe vera could have a positive effect on your digestive tract and help to alleviate digestive tract conditions including irritable bowel syndrome. A study review from 2018 looked at 3 studies with a total of 151 subjects. The results of these studies showed that aloe vera significantly improved symptoms of irritable bowel syndrome compared to a placebo (57). No undesirable side effects were observed. In addition, aloe vera may help inhibit the growth of H. pylori bacteria, which can lead to gastric ulcers (58).

Aloe vera could help against constipation

Aloe vera could help to relieve constipation. In a study of 35 subjects with chronic constipation, aloe vera pills helped to reduce constipation better than a placebo. Patients experienced more regular bowel movements and softer stools and used laxatives less frequently (45). In rats, an aloe-emodin extract from aloe vera showed such a strong laxative effect that it even led to diarrhea (46). Phenolic compounds from aloe vera are responsible for its laxative effects. They stimulate the digestive tract, increase the amount of water in the intestine and stimulate contractions of the intestine (46).

Aloe vera could alleviate heartburn

In a pilot study of 79 gastric acid reflux patients, aloe vera was effective in relieving heartburn and other acid reflux symptoms. Compared to the group receiving omeprazole (a commonly prescribed medication for heartburn), the aloe vera group also had less bloating, nausea, vomiting and other symptoms. Aloe vera was well tolerated and had few side effects (47). As this is only a pilot study, further human studies are needed to confirm these effects.

Aloe vera could improve immune function

Aloe vera contains many antioxidants - vitamins C and E, flavonoids, tannins and carotenoids. By reducing oxidative damage, these antioxidants can protect the immune system (48). In guinea pigs, alprogen (a component of aloe vera) was able to prevent the formation of mast cells. Mast cells are white blood cells that can cause inflammation and hypersensitivity or allergic reactions. By inhibiting the formation of mast cells, alprogene prevented the release of histamines and leukotrienes, thereby preventing allergic reactions (49). Aloe vera also induced white blood cells in mice to release subleukin-1 and tumor necrosis factor (TNF), which stimulates the immune system (50). Aloeride, a sugar contained in aloe vera juice, activates white blood cells (macrophages), which stimulates immune function (51). As the available studies have been conducted exclusively in test tubes and with animals, further human studies are needed to find out whether these effects can be transferred to humans.

Possible side effects

Common side effects of using aloe vera on the skin include (4):

Skin rashes
Burning and stinging

When taken orally, the following side effects have been reported (4):

Diarrhea
vomiting
Stomach cramps
Constipation (in rare cases)

Most of these side effects can cause an electrolyte imbalance, especially with prolonged use. Electrolyte imbalances (especially potassium deficiency) due to prolonged aloe vera use can cause irregular heartbeat and increase the risk of heart failure (52). In some case studies, high oral doses of aloe vera caused kidney failure, hepatitis, liver dysfunction and even hyperthyroidism (4). In mice, high doses of aloe vera reduced brain function. They also damaged sperm, reduced the number of red blood cells and increased the rate of cell death (53). Administration of an aloe vera leaf extract in the drinking water over a two-year period induced the development of intestinal tumors in rats. Aloin was identified as the compound responsible for the development of colon cancer (54).

Are there any safety concerns with aloe?

Aloe gel is likely to be considered safe and harmless when applied to the skin or taken orally. Occasionally, aloe gel may cause burning and itching of the skin.

Aloe Latex may not be safe to ingest, and high doses are unlikely to be safe. Aloe latex can cause side effects such as stomach pain and stomach cramps. Long-term use of large amounts of aloe latex can cause diarrhea, kidney problems, blood in the urine, low potassium levels, muscle weakness, weight loss and heart dysfunction. Taking 1 gram of aloe latex per day for several days can even be fatal. There are some reports of liver problems in people who have taken an aloe leaf extract, but such side effects are the exception rather than the rule. It is believed that such side effects only occur in people who are hypersensitive to aloe.

Precautions and warnings

Pregnant and breastfeeding women: Taking aloe in gel form may not be considered safe and harmless. There are reports that aloe has been linked to miscarriages. For this reason, pregnant or breastfeeding women should not take aloe.
Children: The use of aloe may not be safe for children. Children under the age of 12 may experience abdominal pain, stomach cramps and diarrhea.
Diabetes: Some research suggests that aloe may lower blood sugar levels. For this reason, diabetics taking aloe should monitor their blood sugar levels closely.< br> - Intestinal diseases such as Crohn's disease, ulcerative colitis or constipation: People suffering from these diseases/problems should not take aloe latex as it irritates the intestines. It should be noted that all products made from whole aloe leaves always contain some aloe latex.
Hemorrhoids: People suffering from hemorrhoids should not take Aloe Latex as it can aggravate problems associated with hemorrhoids.
Kidney problems: High dosages of Aloe Latex have been linked to kidney failure and other serious kidney problems.
Surgeries: Aloe can affect blood sugar levels and blood sugar control during surgery. For this reason, you should stop taking aloe two weeks before planned surgery.

Interactions with medications

Aloe should not be combined with the following medications:

Medications for diabetes

Aloe gel can lower blood sugar levels and diabetes medications are also used to lower blood sugar levels. For this reason, the combination of aloe gel with diabetes medication can result in an excessive reduction in blood sugar levels. For this reason, the blood sugar level should be monitored closely with such a combination. The dosage of the diabetes medication may need to be adjusted.

Medication taken orally

When taken orally, aloe latex acts as a laxative. Laxatives can reduce the absorption of medication taken orally. For this reason, Aloe Latex can reduce the effectiveness of ingested medications.

Stimulating laxatives

When taken orally, aloe latex acts as a stimulant laxative. Stimulant laxatives accelerate the intestinal passage of food. Taking Aloe Latex in combination with other stimulant laxatives can speed up intestinal transit too much and lead to diarrhea, dehydration and low mineral levels in the body.

Diuretics

When taken orally, aloe latex acts as a laxative and some laxatives can lower potassium levels in the body. Diuretics can also lower potassium levels, which means that the combination of Aloe Latex with diuretics can lower potassium levels in the body too much.

Interactions with supplements and medicinal herbs

Supplements and medicinal herbs that can lower blood sugar levels:

Aloe can lower blood sugar levels and, when combined with other supplements or medicinal herbs that can also lower blood sugar levels, can cause blood sugar levels to drop too low in some people. Herbs and supplements that can lower blood sugar levels include alpha lipoic acid, bitter melon, devil's claw, fenugreek, garlic, guar gum, horse chestnut, panax ginseng, Siberian ginseng and others.

Medicinal herbs that contain cardiac glycosides

Aloe can lower potassium levels in the body. This poses a particular problem for the heart when aloe is taken in combination with other medicinal herbs that contain chemicals known as cardiac glycosides, which affect the heart's electrical system. Medicinal herbs that contain cardiac glycosides include hellebore, hemp root, digitalis leaves, plantain, brownroot, lily-of-the-valley root, heartleaf, oleander leaves, adonis rose, and pleurisy root.

Horsetail (horsetail) / licorice (licorice)

The combination of aloe with horsetail or licorice can lower potassium levels too much.

Medicinal herbs that act as stimulant laxatives

Combining aloe with medicinal herbs that act as stimulant laxatives increases the risk of potassium levels dropping too low. Such medicinal herbs include blue iris, buckthorn, walnut bark, buckthorn bark, castor oil, bitter melon, gum bark extract, jalapa root, mannar bark extract, Himalayan mayapple root, rhubarb root, senna leaves and husks, and dock root.

Interactions with foodstuffs

Interactions of aloe with foodstuffs are not known.

Recommended dosage and application

The following dosages have been used in scientific studies:

Constipation: 100 to 200 mg aloe or 50 mg aloe latex taken orally in the evening. Note: The use of aloe latex is not considered safe and harmless. Psoriasis: Aloe extract cream 0.5%, applied to the skin three times a day. Sunburn and minor burns: To treat sunburn, aloe vera gel should be applied to the affected areas several times a day.

References

Further sources

Bunyapraphatsara N, Yongchaiyudha S, Rungpitarangsi V, Chokechaijaroenporn O. Antidiabetic activity of Aloe vera L juice. II. Clinical trial in diabetes mellitus patients in combination with glibenclamide. Phytomedicine 1996;3:245-8.
Yongchaiyudha S, Rungpitarangsi V, Bunyapraphatsara N, Chokechaijaroenporn O. Antidiabetic activity of Aloe vera L juice. I. Clinical trial in new cases of diabetes mellitus. Phytomedicine 1996;3:241-3.
Chalaprawat M. The hypoglycemic effects of aloe vera in Thai diabetic patients. J Clin Epidemiol 1997;50(Suppl 1):3S.
Yang HN, Kim DJ, Kim YM, et al. Aloe-induced toxic hepatitis. J Korean Med Sci 2010;25:492-5.
Eshghi F, Hosseinimehr SJ, Rahmani N, et al. Effects of Aloe vera cream on posthemorrhoidectomy pain and wound healing: results of a randomized, blind, placebo-control study. J Altern Complement Med 2010;16:647-50.
Schorkhuber M, Richter M, Dutter A, et al. Effect of anthraquinone laxatives on the proliferation and urokinase secretion of normal, premalignant and malignant colonic epithelial cells. Eur J Cancer 1998;34:1091-8.
Mueller SO, Stopper H. Characterization of the genotoxicity of anthraquinones in mammalian cells. Biochim Biophys Acta 1999;1428:406-14.
Kanat O, Ozet A, Ataergin S. Aloe vera-induced acute toxic hepatitis in a healthy young man. Eur J Int Med 2006;17:589.
Rabe C, Musch A, Schirmacher P, et al. Acute hepatitis induced by an Aloe vera preparation: a case report. World J Gastroenterol 2005;11:303-4.
Bottenberg MM, Wall GC, Harvey RL, Habib S. Oral aloe vera-induced hepatitis. Ann Pharmacother 2007;41:1740-3.
Lee A, Chui PT, Aun CST, et al. Possible interaction between sevoflurane and Aloe vera. Ann Pharmacother 2004;38:1651-4.
Vogler BK, Ernst E. Aloe vera: a systematic review of its clinical effectiveness. Br J Gen Pract 1999;49:823-8.
Williams MS, Burk M, Loprinzi CL, et al. Phase III double-blind evaluation of an aloe vera gel as a prophylactic agent for radiation-induced skin toxicity. Int J Radiat Oncol Biol Phys 1996;36:345-9.
Miller MB, Koltai PJ. Treatment of experimental frostbite with pentoxifylline and aloe vera cream. Arch Otolaryngol Head Neck Surg 1995;121:678-80.
Kaufman T, Kalderon N, Ullmann Y, Berger J. Aloe vera gel hindered wound healing of experimental second-degree burns: a quantitative controlled study. J Burn Care Rehabil 1988;9:156-9.
Gallagher J, Gray M. Is aloe vera effective for healing chronic wounds? J Wound Ostomy Continence Nurs 2003;30:68-71.
Olsen DL, Raub W, Bradley C, et al. The effect of aloe gel/mild soap versus mild soap alone in preventing skin reactions in patients undergoing radiation therapy. Oncol Nurs Forum 2001;28:543-7.
Langmead L, Makins RJ, Rampton DS. Anti-inflammatory effects of aloe vera gel in human colorectal mucosa in vitro. Aliment Pharmacol Ther 2004;19:521-7.
Heggie S, Bryant GP, Tripcony L, et al. A phase III study on the efficacy of topical aloe vera gel on irradiated breast tissue. Cancer Nurs 2002;25:442-51.
Muller MJ, Hollyoak MA, Moaveni Z, et al. Retardation of wound healing by silver sulfadiazine is reversed by Aloe vera and nystatin. Burns 2003;28:834-6.
Syed TA, Ahmad SA, Holt AH, et al. Management of psoriasis with Aloe vera extract in a hydrophilic cream: a placebo-controlled, double-blind study. Trop Med Int Health 1996;1:505-9.
Langmead L, Feakins RM, Goldthorpe S, et al. Randomized, double-blind, placebo-controlled trial of oral aloe vera gel for active ulcerative colitis. Aliment Pharmacol Ther 2004;19:739-47.
Rajasekaran S, Sivagnanam K, Ravi K, Subramanian S. Hypoglycemic effect of Aloe vera gel on streptozotocin-induced diabetes in experimental rats. J Med Food 2004;7:61-6.
Schmidt JM, Greenspoon JS. Aloe vera dermal wound gel is associated with a delay in wound healing. Obstet Gynecol 1991;78:115-7.
Luyckx VA, Ballantine R, Claeys M, et al. Herbal remedy-associated acute renal failure secondary to Cape aloes. Am J Kidney Dis 2002;39:E13.
Cascara sagrada, aloe laxatives, O-9 contraceptives are category II-FDA. The Tan Sheet May 13, 2002.
Food and Drug Administration, HHS. Status of certain additional over-the-counter drug category II and III active ingredients. Final rule. Fed Regist 2002;67:31125-7.
Reynolds T, Dweck AC. Aloe vera leaf gel: a review update. J Ethnopharmacol 1999;68:3-37.
Hutter JA, Salman M, Stavinoha WB, et al. Antiinflammatory C-glucosyl chromone from Aloe barbadensis. J Nat Prod 1996;59:541-3.
Nusko G, Schneider B, Schneider I, et al. Anthranoid laxative use is not a risk factor for colorectal neoplasia: results of a prospective case control study. Gut 2000;46:651-5.
Klein AD, Penneys NS. Aloe vera. J Am Acad Dermatol 1988;18:714-20.
Brinker F. Herb Contraindications and Drug Interactions. 2nd ed. Sandy, OR: Eclectic Medical Publications, 1998.
Gennaro A. Remington: The Science and Practice of Pharmacy. 19th ed. Lippincott: Williams & Wilkins, 1996.
Wichtl MW. Herbal Drugs and Phytopharmaceuticals. Ed. N.M. Bisset. Stuttgart: Medpharm GmbH Scientific Publishers, 1994.
Foster S, Tyler VE. Tyler's Honest Herbal: A Sensible Guide to the Use of Herbs and Related Remedies. 3rd ed, Binghamton, NY: Haworth Herbal Press, 1993.
Newall CA, Anderson LA, Philpson JD. Herbal Medicine: A Guide for Healthcare Professionals. London, UK: The Pharmaceutical Press, 1996.