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Neem - Azadirachta indica

Neem (Azadirachta indica A. Juss), a member of the Meliaceae family, has been used in traditional medicine across South Asia for thousands of years. This review synthesizes current scientific understanding of neem's therapeutic properties, efficacy, safety, and pharmaceutical applications based on peer-reviewed literature.

Image source and license: https://commons.wikimedia.org/wiki/File:Azadirachta_indica_A._Juss._(48913198513).jpg.
Modified by Peter Jorgensen.

Botanical Information

Azadirachta indica A. Juss (family Meliaceae) is commonly known as neem, Indian lilac, margosa tree, or nim. It should not be confused with Melia azedarach (chinaberry tree or Persian lilac), which belongs to the same family but has different chemical constituents and potentially toxic properties. Additionally, "neem" is sometimes erroneously applied to Murraya koenigii (curry leaf tree) in some regions, though they are botanically distinct species.

Active Compounds

Neem contains over 140 biologically active compounds, with the primary bioactive constituents being terpenoids, particularly limonoids such as azadirachtin, nimbin, nimbidin, and salannin. Other important compounds include quercetin, β-sitosterol, polysaccharides, and various organic acids. The distribution and concentration of these compounds vary among different parts of the plant (leaves, bark, seeds, oil).

Therapeutic Applications with Scientific Evidence

Based on peer-reviewed studies, neem has demonstrated efficacy in the following conditions:

• Antimicrobial activity: Strong evidence for antibacterial effects against both gram-positive and gram-negative bacteria, including drug-resistant strains.
• Antifungal properties: Effective against Candida albicans and dermatophytes.
• Antiparasitic effects: Demonstrated efficacy against malaria parasites and intestinal helminths.
• Antidiabetic activity: Multiple clinical trials showing blood glucose-lowering effects.
• Oral/dental health: Significant plaque-reducing and anti-gingivitis effects.
• Hepatoprotective properties: Liver-protective effects against various chemical toxins.
• Immunomodulatory activity: Enhancement of cellular and humoral immune responses.
• Anti-inflammatory effects: Reduction of inflammatory markers and symptoms.
• Dermatological applications: Efficacy in treating acne, psoriasis, and eczema.
• Gastroprotective effects: Protection against gastric ulcers.
• Anticancer potential: In vitro and animal studies showing cytotoxic effects against various cancer cell lines.

Evidence Quality Assessment

The strength of evidence varies considerably across therapeutic applications. The strongest evidence exists for antimicrobial, antidiabetic, and oral health applications, which have been supported by randomized controlled trials. For other applications like anticancer, hepatoprotective, and immunomodulatory effects, evidence is primarily from in vitro and animal studies, with limited high-quality human trials.

Recommended Dosages

Dosages vary based on the part of the plant used and the preparation method. Below are evidence-based dosages that have demonstrated efficacy in clinical studies:

• Neem leaf extract: 250-500 mg twice daily (standardized to 5% bitter principles)
• Neem bark extract: 100-300 mg daily (standardized to 2.5% nimbidin)
• Neem oil: Topical application of 2-5% concentration for skin conditions
• Neem seed extract: 100-200 mg daily (standardized to 10% azadirachtin)
• Dental applications: Toothpaste containing 2-5% neem extract; mouthwash with 10-15 ml of 0.05-0.1% neem extract solution

It's worth noting that standardization varies widely among commercial products, and the azadirachtin content is often used as a marker compound for standardization purposes.

Safety Profile and Side Effects

Neem has a generally favorable safety profile when used at recommended dosages, but several adverse effects have been documented:

• Gastrointestinal disturbances: Nausea, vomiting, and diarrhea (particularly with high doses)
• Hypoglycemia: Potential concern for diabetic patients using antidiabetic medications
• Hepatotoxicity: Rare cases reported with high-dose, prolonged use
• Reproductive effects: Potential spermicidal and anti-fertility effects, contraindicated during pregnancy
• Allergic reactions: Contact dermatitis and hypersensitivity reactions in susceptible individuals
• Drug interactions: May interact with antidiabetic, anticoagulant, and immunosuppressive medications

High-Dose Studies and Knowledge Gaps

Studies investigating doses above the recommended therapeutic range have shown dose-dependent toxicity. Acute toxicity studies in animals have established LD50 values for various neem preparations, but comprehensive human safety data for high doses is limited. Reported toxic effects at high doses include severe liver damage, metabolic acidosis, and encephalopathy. A significant knowledge gap exists regarding long-term safety of regular neem consumption, potential drug interactions, and effects in vulnerable populations such as pregnant women, children, and elderly individuals with comorbidities. Additionally, standardization protocols for neem products vary widely, creating challenges for establishing universal dosing guidelines.

Conclusion

Neem has demonstrated therapeutic potential across multiple health conditions, with the strongest evidence supporting its antimicrobial, antidiabetic, and oral health applications. However, significant variability in preparation methods, lack of standardization, and limited high-quality clinical trials for many indications necessitate cautious interpretation of available evidence. Future research should focus on standardized preparations, well-designed clinical trials, and systematic safety evaluations to better define neem's place in modern medicine.

References

Alzohairy, M. A. (2016). Therapeutics role of Azadirachta indica (Neem) and their active constituents in diseases prevention and treatment. Evidence‐Based Complementary and Alternative Medicine, 2016(1), 7382506.

Arumugam, A., Agullo, P., Boopalan, T., Nandy, S., Lopez, R., Gutierrez, C., ... & Rajkumar, L. (2014). Neem leaf extract inhibits mammary carcinogenesis by altering cell proliferation, apoptosis, and angiogenesis. Cancer biology & therapy, 15(1), 26-34.

Bandyopadhyay, U., Biswas, K., Sengupta, A., Moitra, P., Dutta, P., Sarkar, D., ... & Banerjee, R. K. (2004). Clinical studies on the effect of Neem (Azadirachta indica) bark extract on gastric secretion and gastroduodenal ulcer. Life sciences, 75(24), 2867-2878.

Bhanwra, S., Singh, J., & Khosla, P. (2000). Effect of Azadirachta indica (Neem) leaf aqueous extract on paracetamol-induced liver damage in rats. Indian journal of physiology and pharmacology, 44(1), 64-68.

Hao, F., Kumar, S., Yadav, N., & Chandra, D. (2014). Neem components as potential agents for cancer prevention and treatment. Biochimica et Biophysica Acta (BBA)-Reviews on Cancer, 1846(1), 247-257.

Jalaluddin, M., Rajasekaran, U. B., Paul, S., Dhanya, R. S., Sudeep, C. B., & Adarsh, V. J. (2017). Comparative Evaluation of Neem Mouthwash on Plaque and Gingivitis: A Double-blind Crossover Study. The journal of contemporary dental practice, 18(7), 567-571.

Mahmoud, D. A., Hassanein, N. M., Youssef, K. A., & Abou Zeid, M. A. (2011). Antifungal activity of different neem leaf extracts and the nimonol against some important human pathogens. Brazilian Journal of Microbiology, 42, 1007-1016.

Mathur, S., & Kachhwaha, S. (2015). Neem tree: amazing beauty component in skin and hair care. Advances in Pharmacology and Toxicology, 16(3), 31.

Udeinya, I. J., Mbah, A. U., Chijioke, C. P., & Shu, E. N. (2004). An antimalarial extract from neem leaves is antiretroviral. Transactions of the Royal Society of Tropical Medicine and Hygiene, 98(7), 435-437.

Yarmohammadi, F., Mehri, S., Najafi, N., Amoli, S. S., & Hosseinzadeh, H. (2021). The protective effect of Azadirachta indica (neem) against metabolic syndrome: A review. Iranian journal of basic medical sciences, 24(3), 280.