Herb × Condition

Neem for Eye Disorders

Sanskrit: निम्ब | Azadirachta indica A. Juss.

How Neem helps with Eye Disorders according to Ayurveda. Classical references, dosage, preparation methods, and what modern research says.

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Neem for Eye Disorders: Does It Work?

Does Neem (Nimba, Azadirachta indica) help with eye disorders (Netra Roga)? Yes, with a sharply defined role: Neem is the named classical herb for infective and suppurative eye disease, the red, weeping, pus-forming end of the conjunctivitis spectrum. The Sushruta Samhita places Neem inside the chapters on Raktabhishyanda (blood-type conjunctivitis) and prescribes a Neem-based Anjana (collyrium) for Netra-paka, eye suppuration.

Jasmine flowers, saindhava (rock salt), shringavera (ginger), krisna (black pepper) seeds, and the essence of kitashatru (neem), this ground preparation with honey should be fearlessly applied as anjana in netra-paka (eye suppuration).

Sushruta Samhita, Uttara Tantra, Chapter 12: Raktabhishyanda Pratishedha Adhyaya

The Ayurvedic case rests on Neem's deep antimicrobial and Pitta-cooling profile. The Bhavaprakash Nighantu classifies Nimba as antifungal, antibacterial, antiviral, and antiparasitic, with a bitter taste (Tikta Rasa) that pacifies Pitta and Kapha alike. For the eye, those two doshas together describe most infective and allergic presentations: Pitta heat drives the redness and burning, Kapha drives the discharge and sticky lid margins. Neem's specific phytochemistry, Nimbin, Nimbidin, Azadirachtin, and the limonoids identified in seed and bark, supports the classical claim of broad antimicrobial action.

Neem is the lead pick for infective and Kapha-Pitta eye disease: bacterial conjunctivitis with thick or yellow discharge, suppurative blepharitis, weeping lid-margin infection, and the post-viral or fungal lid involvement that turmeric alone cannot clear. It is also a useful adjunct for chronic allergic conjunctivitis where the lid margin is colonised. It is not the right herb for dry, gritty Vata eye strain, for cataract, or for the cool Pitta-cooling job that Aloe Vera and rose water handle better.

How Neem Helps with Eye Disorders

Most inflammatory eye disease in Ayurveda is read as a disturbance of Alochaka Pitta, the sub-dosha of Pitta seated in the eye. When that disturbance turns infective, red eye with thick discharge, swollen suppurating lid margin, sticky crusting on waking, the picture moves into the Pitta-Kapha overlap. This is the domain where Neem does its specific work.

Krimighna and Kushthaghna action against eye-surface pathogens

The Bhavaprakash Nighantu describes Nimba as antifungal, antibacterial, antiviral, and antiparasitic, and classifies it as Krimighna (anti-parasitic, in classical usage a broad antimicrobial) and Kushthaghna (the foremost drug for skin diseases). The lid margin is, anatomically and from the Ayurvedic standpoint, a skin surface, and chronic infective blepharitis behaves like a localized Kushtha. Neem's named action on this tissue layer is what makes the bark, leaf, and seed-oil preparations the classical choice for infective lid disease.

Tikta Rasa and Pitta-Kapha Shamaka effect on inflamed channels

Neem's bitter taste (Tikta Rasa) is one of the most strongly Pitta-pacifying and Kapha-pacifying rasas in the classical pharmacology. For the eye, bitter taste reduces the burning and redness of Pitta and dries the sticky discharge of Kapha simultaneously. This dual action is what fits the herb to infective conjunctivitis with discharge, where the cool-only herbs (Aloe Vera, rose water) reduce burning but do not clear the Kapha-pattern mucus.

Anjana tradition for suppurative eye disease

The Sushruta Samhita places Neem inside a named Anjana (collyrium) formulation for Netra-paka, the suppurative eye, alongside honey, rock salt, ginger, and black pepper. The principle is direct topical antimicrobial delivery to an infected eye surface. This is a specialist procedure not appropriate for home replication, but it establishes the classical authority for using Neem in the most serious end of the infective spectrum.

Where Neem sits in the eye-care toolkit

Neem does not replace Triphala as the daily Rasayana eye wash, nor Amla as the internal Chakshushya, nor Aloe Vera as the cooling topical for pure Pitta flares. Its lane is infective and suppurative lid disease, and Kapha-Pitta conjunctivitis with discharge. Used outside that lane, the bitter and slightly drying quality is unnecessary and the cooler, gentler herbs do the job better.

How to Use Neem for Eye Disorders

Never put neem leaf juice or seed oil directly into the eye

The classical Anjana formulation described in the Sushruta Samhita is a specialist preparation, not a home remedy. Raw Neem leaf juice and unprepared Neem seed oil are far too strong for the open eye and will cause sharp irritation, lacrimation, and possible chemical injury to the cornea. All home use of Neem for eye disorders works either through internal use, through eye wash with dilute decoction filtered to surgical sterility, or topically on the closed lid.

Neem leaf decoction eye wash for infective lid margin disease

For suppurative blepharitis and chronic infective lid margin disease, the home protocol is a Neem leaf decoction used as a closed-eye wash. Boil a small handful of fresh, clean Neem leaves in two cups of water for ten minutes, cool to body temperature, strain through fine muslin two or three times until the liquid is perfectly clear, and use that liquid to splash on closed eyes morning and evening. Discard after each use; do not store.

Internal Neem leaf decoction for Kapha-Pitta conjunctivitis

For systemic support during a bacterial or allergic conjunctivitis flare, take a teaspoon of fresh Neem leaf juice (or 250 to 500 mg Neem leaf powder) on an empty stomach, mixed with a teaspoon of honey to mask the strong bitter taste. This is the classical 1-2 tola dose adapted to modern home practice. Take for five to seven days only, the bitter, slightly drying quality is not for chronic daily use.

Dosage table

FormDoseAnupana / useIndication
Neem leaf decoction (external wash)Handful leaves in 2 cups water, boiled and strained 2-3 timesSplashed on closed eyesInfective lid margin disease, blepharitis
Neem leaf juice (internal)1 tsp (or 250-500 mg powder)With honey, empty stomachBacterial/allergic conjunctivitis with discharge
Panchanimba Churna1-3 gWarm water, twice daily after mealsChronic recurrent infective eye disease with skin involvement

Anupana tuned to the eye pattern

For Pitta-Rakta hot, deep red eyes with discharge, pair internal Neem with honey and consider adding Turmeric golden milk at night for a wider anti-inflammatory effect. For Kapha-pattern thick discharge with chronic recurrence, take Neem with warm water and a pinch of black pepper to amplify the Kapha-clearing action. Daily Triphala eye wash sits alongside any Neem protocol as the baseline.

Duration expectations

Acute bacterial conjunctivitis with discharge typically improves within five to seven days of combined internal Neem and external decoction wash. Chronic infective blepharitis needs two to four weeks of consistent external wash plus correction of the underlying lid hygiene. Do not exceed two weeks of continuous internal Neem leaf use; the bitter quality begins to dry the channels. If there is no improvement within 48 hours, vision is affected, or the discharge is increasing, see an ophthalmologist; some infections need prescription antibiotic drops.

Frequently Asked Questions

Can I put neem oil or neem juice directly into my eyes?

No. Raw Neem leaf juice and Neem seed oil are far too strong for the open eye and will cause stinging, tearing, and possible chemical irritation. The classical Anjana formulation that contains Neem essence is a specialist preparation with honey and other ingredients, not a home remedy. For home use, restrict Neem to closed-eye decoction wash (filtered through fine muslin two or three times) and internal use with honey.

How long does Neem take to work for conjunctivitis or lid infection?

Acute bacterial conjunctivitis with discharge typically improves within five to seven days of combined internal Neem leaf juice with honey and external decoction eye wash. Chronic infective blepharitis needs two to four weeks. If there is no improvement within 48 hours, vision is affected, or discharge is increasing, see an ophthalmologist. Neem complements antibiotic drops, it does not replace them in serious infection.

What is the best form of Neem for eye disorders?

It depends on the layer of disease. For infective lid margin and blepharitis, the Neem leaf decoction used as a closed-eye wash is the home gold standard. For systemic infective conjunctivitis with discharge, fresh Neem leaf juice or 250-500 mg leaf powder with honey internally. For chronic recurrent eye disease with skin involvement, the classical Panchanimba Churna (using all five parts of the tree) at 1-3 g with warm water twice daily. Avoid raw Neem oil near the eyes.

Neem vs Triphala or Turmeric for eye disorders?

These cover different layers. Triphala is the daily tridoshic eye wash and internal Rasayana, baseline for everyone. Turmeric is the anti-inflammatory for sties and inflamed lid margins, applied as paste on the closed lid. Aloe Vera is the cooling Pitta-pacifying compress for hot, burning eyes. Amla is the internal Chakshushya Rasayana. Neem's lane is the infective, suppurative, discharging end: bacterial conjunctivitis, suppurative blepharitis, and chronic infective lid disease where antimicrobial action is what you need.

Safety & Precautions

Neem is a powerful medicine, not a mild daily tonic. Used correctly it is remarkably safe, but it has a handful of specific contraindications that every user should know about. Several of these are well documented in both classical and modern literature.

Do Not Use During Pregnancy

This is the single most important warning. Neem has well-documented anti-fertility and abortifacient effects in both classical Ayurveda and modern animal studies. Neem seed oil in particular has been studied as a contraceptive. Avoid Neem in any form, leaf, bark, oil, or supplement, if you are pregnant or trying to conceive.

Fertility Reduction (Both Sexes)

Neem reduces sperm motility in men and interferes with implantation in women. If you are actively trying to conceive, stop Neem at least 2-3 months beforehand. This same effect is why Neem has been studied as a reversible natural contraceptive.

Blood Sugar Interactions

Neem lowers blood sugar. If you are taking insulin, metformin, sulfonylureas, or other anti-diabetic medication, Neem can push blood sugar too low (hypoglycemia). Use only under medical supervision and monitor your levels closely when adding or stopping Neem.

Never Ingest Neem Seed Oil

Neem leaf preparations are used internally. Neem seed oil is for external use only. Swallowing neem oil, even small amounts, has caused serious poisoning, especially in infants and children, with symptoms including vomiting, seizures, metabolic acidosis, and Reye-like encephalopathy. Keep neem oil locked away from children.

G6PD Deficiency

People with G6PD deficiency should avoid Neem. Some compounds in Neem can trigger hemolytic anemia in this population. If you have not been tested and are of Mediterranean, African, or South Asian heritage, ask your doctor before using Neem.

Vata Aggravation and Depletion

The Bhavaprakasha Nighantu notes that Neem is not ideal for people with high Vata, debility, emaciation, or cold signs. It is cooling, drying, and depleting when overused. People who are already thin, weak, dry, anxious, or convalescing should use Neem sparingly and short-term, ideally paired with a warming, nourishing herb.

Other Cautions

  • Children under 2: Avoid all internal Neem. External use of diluted neem oil for lice or skin conditions is acceptable under adult supervision.
  • Autoimmune conditions: Neem is an immune modulator. Those on immunosuppressant drugs should consult their physician.
  • Surgery: Stop Neem at least two weeks before any scheduled surgery because of its effects on blood sugar and immune response.
  • Heart conditions: The Bhavaprakasha notes Neem can be burdensome to the heart in excess, keep doses moderate.

For healthy adults using typical food-level or short-course therapeutic doses, Neem is well tolerated. Most reported adverse events involve neem seed oil ingestion, unusually high doses, or use during pregnancy.

Other Herbs for Eye Disorders

See all herbs for eye disorders on the Eye Disorders page.

Classical Text References (6 sources)

Nimbi Taila – (Neem oil) :ना यु णं न बजं त तं कृ मकु ठकफ णुत ् ॥ ६० ॥ Neem oil – is not very hot (slightly hot) in potency, bitter, anti microbial, useful in skin diseases and mitigates Kapha.

— Astanga Hridaya, Chapter 5: Drava Vigyaniya Drinkables

74 पटोलस तला र टशा गे टाव गुजा अम ृताः वे ा ब ृहतीवासाकु तल तलप णकाः म डूकपण कक टकारवे लकपपटाः नाडीकलायगोिज वावाताकं वन त तकम ् कर रं कु कं न द कुचैला शुकलादनी क ट लं के बुकं शीतं सकोशातकककशम ् त तं पाके कटु ा ह वातलं कफ प तिजत ् Patola, saptala, arista (neem leaves), sharngeshta (angaravalli/bharangi), Avalguja (Bakuchi), amruta (Tinospora), Vetra (shoot of vetra), Brhati (Solanum indicum), vasa (Adhatoda vasica), kutill, tilaparnika (badraka), mandukaparni (Gotu kola), Karkota, karavella

— Astanga Hridaya, Chapter 6: Annaswaroopa Food

Tikta Gana – group of bitters :त तः पदोल ाय ती वालकोशीर च दनम ् भू न ब न ब कटुका तगरा गु व सकम ् न तमाला वरजनी मु त मूवाट पकम पाठापामागकां यायोगुडू चध वयासकम ् प चमल ू ं महा या यौ वशाल अ त वषावचा Patoli, Trayanti – Gentiana kurroa, Valaka, Usira – Vetiveria zizanioides, Chandana – Sandalwood, Bhunimba – The creat (whole plant) – Andrographis paniculata, Nimba – Neem – Azadirachta indica, Katuka – Picrorhiza kurroa, Tagara – Indian Valerian (root) – Valeriana wallichi, Aguru, Vatsaka – Hol

— Astanga Hridaya, Chapter 10: Rasabhediyam Tastes, Their

Tikta Gana – group of bitters :त तः पदोल ाय ती वालकोशीर च दनम ् भू न ब न ब कटुका तगरा गु व सकम ् न तमाला वरजनी मु त मूवाट पकम पाठापामागकां यायोगुडू चध वयासकम ् प चमल ू ं महा या यौ वशाल अ त वषावचा Patoli, Trayanti – Gentiana kurroa, Valaka, Usira – Vetiveria zizanioides, Chandana – Sandalwood, Bhunimba – The creat (whole plant) – Andrographis paniculata, Nimba – Neem – Azadirachta indica, Katuka – Picrorhiza kurroa, Tagara – Indian Valerian (root) – Valeriana wallichi, Aguru, Vatsaka – Hol

— Astanga Hridaya, Chapter 10: Rasabhediyam Tastes, Their

The wound should be fumigated with the smoke of Guggulu, Aguru, Siddhartha, Hingu (Asa foetida), Sarjarasa, Patu (Salt), Sadgrantha(Acorus calamus) or leaves of Nimba (neem), mixed with ghee; Then a wick prepared from paste of Tila, ghee, honey and appropriate drugs should be placed inside the wound and also covered over.

— Astanga Hridaya, Chapter 29: Shastrakarma Vidhi

The wound should be fumigated with the smoke of Guggulu, Aguru, Siddhartha, Hingu (Asa foetida), Sarjarasa, Patu (Salt), Sadgrantha(Acorus calamus) or leaves of Nimba (neem), mixed with ghee; Then a wick prepared from paste of Tila, ghee, honey and appropriate drugs should be placed inside the wound and also covered over.

— Astanga Hridaya, Chapter 29: Shastrakarma Vidhi

Source: Astanga Hridaya, Ch. 5, Ch. 6, Ch. 10, Ch. 10, Ch. 29, Ch. 29

Nimbi Taila – (Neem oil) :ना यु णं न बजं त तं कृ मकु ठकफ णुत ् ॥ ६० ॥ Neem oil – is not very hot (slightly hot) in potency, bitter, anti microbial, useful in skin diseases and mitigates Kapha.

— Astanga Hridaya Sutrasthan, Drava Vigyaniya Drinkables

74 पटोलस तला र टशा गे टाव गुजा अम ृताः वे ा ब ृहतीवासाकु तल तलप णकाः म डूकपण कक टकारवे लकपपटाः नाडीकलायगोिज वावाताकं वन त तकम ् कर रं कु कं न द कुचैला शुकलादनी क ट लं के बुकं शीतं सकोशातकककशम ् त तं पाके कटु ा ह वातलं कफ प तिजत ् Patola, saptala, arista (neem leaves), sharngeshta (angaravalli/bharangi), Avalguja (Bakuchi), amruta (Tinospora), Vetra (shoot of vetra), Brhati (Solanum indicum), vasa (Adhatoda vasica), kutill, tilaparnika (badraka), mandukaparni (Gotu kola), Karkota, karavella

— Astanga Hridaya Sutrasthan, Annaswaroopa Food

Tikta Gana – group of bitters :त तः पदोल ाय ती वालकोशीर च दनम ् भू न ब न ब कटुका तगरा गु व सकम ् न तमाला वरजनी मु त मूवाट पकम पाठापामागकां यायोगुडू चध वयासकम ् प चमल ू ं महा या यौ वशाल अ त वषावचा Patoli, Trayanti – Gentiana kurroa, Valaka, Usira – Vetiveria zizanioides, Chandana – Sandalwood, Bhunimba – The creat (whole plant) – Andrographis paniculata, Nimba – Neem – Azadirachta indica, Katuka – Picrorhiza kurroa, Tagara – Indian Valerian (root) – Valeriana wallichi, Aguru, Vatsaka – Hol

— Astanga Hridaya Sutrasthan, Rasabhediyam Tastes, Their

The wound should be fumigated with the smoke of Guggulu, Aguru, Siddhartha, Hingu (Asa foetida), Sarjarasa, Patu (Salt), Sadgrantha(Acorus calamus) or leaves of Nimba (neem), mixed with ghee;

— Astanga Hridaya Sutrasthan, Shastrakarma Vidhi

Source: Astanga Hridaya Sutrasthan, Drava Vigyaniya Drinkables; Annaswaroopa Food; Rasabhediyam Tastes, Their; Shastrakarma Vidhi

In order to clean the seat of kapha and amashaya, the patient should be given the decoction of pippali, sarsapa (yellow sarson/Indian colza/Brassica campestris) and nimba (neem tree/Margosa/Indian lilac/Azadirachta indica) added with powder of pinditaka (madanaphala/emetic nut/bushy gardenia/Randia dumetorum) and saindhava (rock-salt).

— Charaka Samhita, Chikitsa Sthana — Therapeutic Principles, Chapter 20: Vomiting Treatment (Chhardi Chikitsa / छर्दिचिकित्सा)

Source: Charaka Samhita, Chikitsa Sthana — Therapeutic Principles, Chapter 20: Vomiting Treatment (Chhardi Chikitsa / छर्दिचिकित्सा)

Take rāsnā, vāsā, arka, triphalā, vidanga, bark of sigru, mushakaparni, neem, holy basin, nails of vyāghra (shell), durvā, sunflower, katukā, kākamāchi, brihati, kuṣtha, punarnavā, chitraka and dry ginger and make paste with cow’s urine.

— Charaka Samhita, Chikitsa Sthana — Therapeutic Principles, Chapter 12: Edema Treatment (Shvayathu Chikitsa / श्वयथुचिकित्सा)

In order to clean the seat of kapha and amashaya, the patient should be given the decoction of pippali, sarsapa (yellow sarson/Indian colza/Brassica campestris) and nimba (neem tree/Margosa/Indian lilac/Azadirachta indica) added with powder of pinditaka (madanaphala/emetic nut/bushy gardenia/Randia dumetorum) and saindhava (rock-salt).

— Charaka Samhita, Chikitsa Sthana — Therapeutic Principles, Chapter 20: Vomiting Treatment (Chhardi Chikitsa / छर्दिचिकित्सा)

The soup which is used for purification of breast milk, should be prepared with tender leaves of neem and vetra, parvala leaves, brinjal and amalaka added with dry zinger (shunthi), pepper, pippali and rock salt.

— Charaka Samhita, Chikitsa Sthana — Therapeutic Principles, Chapter 30: Gynecological Disorders Treatment (Yonivyapat Chikitsa / योनिव्यापत्चिकित्सा)

Source: Charaka Samhita, Chikitsa Sthana — Therapeutic Principles, Chapter 12: Edema Treatment (Shvayathu Chikitsa / श्वयथुचिकित्सा); Chikitsa Sthana — Therapeutic Principles, Chapter 20: Vomiting Treatment (Chhardi Chikitsa / छर्दिचिकित्सा); Chikitsa Sthana — Therapeutic Principles, Chapter 30: Gynecological Disorders Treatment (Yonivyapat Chikitsa / योनिव्यापत्चिकित्सा)

That which penetrates the subtle channels (Sukshma-chhidra) of the body is called Sukshma (subtle/penetrating), like Saindhava (rock salt), honey, Nimba taila (neem oil), and substances born of Eru (castor).

— Sharangadhara Samhita, Purva Khanda, Chapter 4: Dipana-Pachana Adikathanam (Digestive Actions etc.)

Pathyadi Kvatha: Pathya (Haritaki — Terminalia chebula), Nimba (neem — Azadirachta indica), Nidigdhika (Solanum xanthocarpum), Kiratatikta (Swertia chirayita), Guduchi (Tinospora cordifolia), and Chandana (sandalwood — Santalum album) decoction alleviates Pitta Jvara (fever caused by Pitta).

— Sharangadhara Samhita, Madhyama Khanda, Chapter 1: Svarasadikalpana (Svarasa, Kalka, Kvatha, etc.)

Panchanimba Churna [for Kushtha/skin diseases]: the root, leaves, fruits, flowers, and bark of Nimba (neem — Azadirachta indica) should be collected.

— Sharangadhara Samhita, Madhyama Khanda, Chapter 6: Churnakalpana (Powder Preparations - Extended)

Bibhitaka, Nimba (neem), Gambhari, Shiva, Shelu, Kakini — oil Nasya with each individually surely destroys premature greying.

— Sharangadhara Samhita, Uttara Khanda, Chapter 8: Nasya Vidhi (Nasal Therapy)

Alternatively, the barks of Khadira (Acacia catechu), Arishta (Azadirachta indica/neem), and Jambu (Syzygium cumini/black plum), combined with urine, or Kutaja bark (Holarrhena antidysenterica) with Saindhava (rock salt) as a paste, also destroys Arunshika (scalp dermatitis).

— Sharangadhara Samhita, Uttara Khanda, Chapter 11: Lepa Vidhi (Topical Paste Application)

Source: Sharangadhara Samhita, Purva Khanda, Chapter 4: Dipana-Pachana Adikathanam (Digestive Actions etc.); Madhyama Khanda, Chapter 1: Svarasadikalpana (Svarasa, Kalka, Kvatha, etc.); Madhyama Khanda, Chapter 6: Churnakalpana (Powder Preparations - Extended); Uttara Khanda, Chapter 8: Nasya Vidhi (Nasal Therapy); Uttara Khanda, Chapter 11: Lepa Vidhi (Topical Paste Application)

Then, fumigate the wound area with powders of Guggulu (Commiphora mukul), Aguru (Aquilaria agallocha), Sarja-rasa (Vateria indica resin), Vacha (Acorus calamus), white mustard (Sinapis alba), mixed with salt and Neem (Azadirachta indica) leaves, and anoint the vital points with ghee (18).

— Sushruta Samhita, Sutra Sthana, Chapter 5: Agropaharaniya Adhyaya - Surgical Instruments and Procedures

Post-operative fumigation with antimicrobial herbs (Neem, Guggulu, Vacha are all proven antiseptics).

— Sushruta Samhita, Sutra Sthana, Chapter 5: Agropaharaniya Adhyaya - Surgical Instruments and Procedures

Iron filings, copper dust, neem exudate collyrium, tin, and bronze residue — ground with flower juice.

— Sushruta Samhita, Uttara Tantra, Chapter 12: Raktabhishyanda Pratishedha Adhyaya (Chapter on Treatment of Blood-type Conjunctivitis)

Jasmine flowers, saindhava (rock salt), shringavera (ginger), krisna (black pepper) seeds, and the essence of kitashatru (neem) — this ground preparation with honey should be fearlessly applied as anjana in netra-paka (eye suppuration).

— Sushruta Samhita, Uttara Tantra, Chapter 12: Raktabhishyanda Pratishedha Adhyaya (Chapter on Treatment of Blood-type Conjunctivitis)

Vulture and owl droppings, the skin of a goat and buffalo, neem leaves, and Madhuka (licorice) should be used for fumigation.

— Sushruta Samhita, Uttara Tantra, Chapter 34: Shitaputanapratishedha

Source: Sushruta Samhita, Sutra Sthana, Chapter 5: Agropaharaniya Adhyaya - Surgical Instruments and Procedures; Uttara Tantra, Chapter 12: Raktabhishyanda Pratishedha Adhyaya (Chapter on Treatment of Blood-type Conjunctivitis); Uttara Tantra, Chapter 34: Shitaputanapratishedha

Medical Disclaimer: The information on this page is for educational purposes only and is not intended as medical advice. Ayurvedic treatments should be pursued under the guidance of a qualified practitioner (BAMS/MD Ayurveda). Always consult your healthcare provider before starting any new treatment. Content is sourced from classical Ayurvedic texts and may not reflect the latest medical research.