Neem: a genuinely useful plant with a genuinely serious caution

Azadirachta indica is used extensively across South Asia — leaves, bark, seeds and oil — for skin conditions, dental care, as an insect repellent and agriculturally as a pesticide.

It has some of the better evidence among Ayurvedic botanicals for certain uses, and a serious documented toxicity that is not widely enough known.

The serious warning first

Neem oil taken internally is toxic, particularly to infants and young children, and has caused deaths.

A recognised syndrome of neem oil poisoning in children is documented in the medical literature, involving vomiting, drowsiness, seizures, metabolic acidosis and encephalopathy, with fatalities reported.

The practice of giving neem oil to infants for various complaints has been the subject of published case series and public health warnings in India and elsewhere.

Neem oil should never be given internally to infants or children. Adults should not take neem oil internally either, and neem seed extracts should be treated with considerable caution.

This is the single most important thing on this page.

Where the evidence is reasonable

Dental and oral health. Neem twigs have been used as chewing sticks for a very long time, and neem-based mouthwashes and gels have been studied.

Several trials report reductions in plaque and gingivitis measures, some comparing favourably with standard antiseptic mouthwash. Study quality is variable and the direction of findings is reasonably consistent.

Insect repellent and larvicide. Neem-based preparations have demonstrated activity against mosquito larvae and some repellent effect. Agricultural use of neem as a botanical pesticide is established.

For personal protection against mosquito-borne disease, established repellents have far better evidence, and this matters where malaria or dengue is present.

Topical skin use. Traditional use for skin conditions is extensive. Clinical evidence is limited, with small studies in scabies, acne and other conditions. Some laboratory antimicrobial and antifungal activity is documented.

Head lice. Some studies of neem-based preparations report efficacy.

Where evidence is weak or absent

Internal use for blood sugar, for immunity, for parasites and for a broad range of internal conditions has limited human evidence, and internal use carries the toxicity concerns above.

Laboratory studies reporting a wide range of activities exist in quantity and, as always, do not establish clinical effect.

Additional safety considerations

Pregnancy. Neem has documented effects on fertility and has been investigated as a contraceptive agent. It should be avoided in pregnancy and by anyone trying to conceive.

Fertility. Effects on sperm and on implantation have been reported in animal studies. Relevant for anyone attempting conception.

Autoimmune conditions. Proposed immunostimulant effects raise theoretical concerns.

Blood glucose. Possible glucose-lowering effects, relevant for anyone on diabetes medication.

Children. Beyond the oil toxicity, internal neem preparations of any kind should not be given to children without medical supervision.

Surgery. Discontinue well before planned procedures.

What this case illustrates

Neem is a good example of why the natural-therefore-safe assumption is a bad one, and of why the distinction between topical and internal use matters enormously.

A plant with real, demonstrable biological activity — which is what makes it potentially useful — is by that same fact capable of causing harm. Pharmacological activity does not distinguish between wanted and unwanted effects.

It also illustrates the importance of the specific preparation. Neem leaf, neem bark, neem oil and neem seed extract are different materials with different constituents and different risk profiles. Advice about one does not transfer to another, and product labels are frequently unclear about which is present.

Reasonable use

Topical and dental applications, using products intended for those purposes, are the applications with the best combination of evidence and safety.

Internal use is not something to undertake casually, and neem oil internally should not be undertaken at all.

If you have neem oil in the house and there are children in it, treat it as you would any other potentially toxic substance and store it accordingly.

Never give neem oil internally to infants or children. If neem oil has been ingested by a child, seek emergency medical attention immediately. Avoid neem in pregnancy and when trying to conceive.