Castor Oil - Herbal Monograph Series

Written By Dr. Colleen Huber

Photos from https://southwestdesertflora.com/WebsiteFolders/All_Species/Euphorbiaceae/Ricinus%20communis,%20Castorbean.html

Ricinus communis oil, cold-pressed

Uses

  • Top topical treatment for osteoarthritis, other joint pain and inflammation

  • Top treatment for dry eyes and blepharitis

  • One of the top five plants for hair growth and hair thickening

  • One of the top plants for constipation, topical or oral

  • Anxiolytic

 

For osteoarthritic knee pain

Castor oil was known in Latin as “Oleum Palmae Christi,”¹ literally the oil of the palms or hands of Christ. This likely had to do with the use of castor oil in healing wounds, as well as the shape of the leaf resembling an open hand.

Pliny the Elder, of AD 23 Rome, described the use of castor oil for joints, among other uses.²

In a controlled clinical trial, seniors with knee pain began the trial with an average reported pain level of 7.2 out of ten. They were given topical castor oil, 10 ml to massage on the knees daily, followed by heat application for ten minutes. The control group received neither castor oil nor heat applications. The trial went on for 24 days. The castor oil plus heat group had a 49% improvement in their reported level of pain, whereas the control group had a 7.5% improvement.³

Another study compared the use of topical castor oil to the use of topical heat for joint pain over the course of seven days. Although both treatments were found to be effective, heat reduced pain by 50% in that week, whereas castor oil reduced pain by 57%.⁴

 

For dry eyes, floaters and blepharitis

Meibomian glands make oil for tears, so that tears don’t evaporate quickly, keeping the surface of the eyes lubricated.  A deficiency of this fluid is commonly known as “dry eyes,” formally known as meibomian gland dysfunction.⁵ ⁶

Even very low concentration of castor oil, 2%, along with 5% polyoxyethylene castor oil, was found to be better than saline eyedrops for improving tear function and especially stability of lubrication. 

Floaters are loose aggregates of protein in the vitreous, visible as usually faint ripples or shapes or shadows in front of the viewer’s visual field.  They result from posterior vitreous detachment of pieces of membrane from the retina.  It is a common experience in senior years, as the vitreous becomes less gelatinous and more liquid.  Floaters can also be a manifestation of a serious disease, uveitis.

Although many people have reported on social media that floaters disappear after a week to a month of applying castor oil, and dry eyes improve in an even shorter period after topical application of castor oil to closed eyelids, there is almost no information in the medical literature about the value of castor oil for floaters.

Dr. J. Green wrote in the year 1875 about applying a solution of castor oil and atropine sulfate to the  inner upper eyelid to successfully treat corneal abrasions and corneal ulcers, as well as phlyctenulae and photophobia.⁷ Atropine sulfate must be used only by experienced physicians, with caution, and under medical supervision.

Blepharitis is an inflammation of the eyelid margin, sometimes with thickening and / or dandruff and / or loss of eyelashes or matting of eyelashes.  Pure cold-pressed castor oil was applied to one eyelid twice per day for four weeks in 26 blepharitis patients, while not treating the other eyelid.  The treated eye improved in all patients during that time, and without adverse reactions.⁸

 

For hair growth and prevention of hair loss

When castor oil was combined with rosemary oil, the increase in hair density on mice was greater than other cohorts in which either of those oils were used alone, and showed equivalent effect to the drug minoxidil. The effect was seen to be during the anagen phase.⁹ In a double-blind randomized controlled study in human subjects with a rosemary oil / castor oil combination, hair thickness increased by 66%, and hair density increased by 32% over the course of the 90 days of the study.¹⁰    

Two tablespoons of castor oil combined with five drops of rosemary essential oil is a common combination that may be massaged into the scalp and left on for 30 minutes before shampooing.  Before that, try a patch test of the mixture the day before on a small area of the inner forearm to check for tolerance. If the patch test is successful, then half-hour to overnight application to the scalp may be used.  If the mixture feels too viscous to arrive to the skin of the scalp, it may either be slightly heated to lukewarm, or it may be diluted with a little extra-virgin, cold-pressed olive oil.

 

For constipation

Dr. Charles Phillips in 1879 described castor oil as “a highly valuable evacuant, also for children . . . and, for infants, it is the safest of cathartics.” He explains: “As a laxative, it operates so speedily and mildly, that it is constantly resorted to where similar operation by medicines of a more powerful nature may cause injury.”¹¹

The ancient Greek physician Dioscorides wrote 2,000 years ago: “Taken as a drink it draws out watery matter through the bowels, and it also draws out worms.”¹²

The Ebers Papyrus of 1534 BC discusses castor oil as a laxative.¹³

 

For anxiety

At only 0.5 mL/kg, which was 2.5% of the dose of castor oil used as a laxative, male mice showed fewer measures of anxiety-like behavior after injection with castor oil than after injection with saline.¹⁴

 

Pharmacology and Mechanisms of Action

The U.S. FDA has approved castor oil for ophthalmic, nasal, oral, topical and intramuscular uses.¹⁵ It is classified by the FDA as safe and effective for use as a stimulant laxative.  Castor oil is made by cold-pressing the seeds.  It does not contain ricin, because the ricin is excluded in the cold-pressing process.¹⁶

In topical use

Castor oil is the pharmacologically active extract in common use from the Ricinus communis plant.  As other triglycerides, it has a glycerol backbone and three fatty acid chains.  The fatty acids are mostly ricinoleic acid, which is an omega-9 fatty acid, as is oleic acid in olive oil, as well as grapeseed oil.  Castor oil is a humectant, meaning a moisture rich substance, and it excels at that role to such a commercially viable extent that its highest reported use concentration (81%) is in lipstick.  That is, four-fifths of some lipsticks are castor oil.¹⁷

The ricinoleic acid molecule resembles eicosapentanoic acid of fish oil, which has anti-inflammatory effects.  The ricinoleic acid molecule is remarkable for its low molecular weight, which allows it to pass through the epidermis and dermis, and to be absorbed into the circulatory system.  This enables castor oil to function as a carrier molecule with substances that accompany it.

For this reason, castor oil must be kept exceptionally clean.  Any substance will be carried with it through the skin and into the bloodstream.  So it is important to make sure that the castor oil used is “extra virgin,” meaning cold-pressed, and that it is prepared without solvents such as hexane.

For this reason also, castor oil must be stored only in glass.  Phthalates as well as bisphenol A (BPA) in plastic can be carried into the body if castor oil has leeched these from a plastic container.

Castor oil’s main mechanisms of action against the sensation of pain are 1) to decrease and to disrupt Substance P pathways, and 2) to bind EP3 prostanoid receptors, which significantly reduces the production of prostaglandin E2.¹⁸ This was a result of ricinoleic acid’s effect as an agonist of EP3 / EP4 receptors.¹⁹ The role of Substance P in pain is to increase glutamate-induced currents in major neurons, and to thus amplify pain, and to sensitize the sufferer to pain,²⁰ even to the point were mild touch can hurt.  Capsaicin from cayenne peppers also reduces Substance P, but there is a stinging pain from use of capsaicin, a disadvantage that castor oil does not have.  So castor oil, in reducing Substance P and prostaglandin E2, works against both of those pain pathways in a way that is comfortable for the patient.  The sensation of castor oil on the skin is often described as soothing.

Castor oil also inhibits prostaglandin D2, which is useful to combat male pattern baldness, also known as androgenic alopecia.²¹ Prostaglandin D2 was found to be more abundant on a bald scalp than on a haired scalp.  A study on mice found that prostaglandin D2 had caused miniaturization of hair follicles.²² Castor oil’s effect is to block the synthesis of prostaglandins D2 and E2.

Used topically on eyelids

Castor oil contains monounsaturated fatty acids. From topical application on the eyelids, it is known to deposit into the highly lipophilic retina and uveal tissues, such as the choroid and the ciliary body.²³ Floaters are a manifestation of uveitis, as well as a common condition of aging. These have been treated successfully with castor oil, as therapeutic concentrations of a castor oil based eyedrops were found to arrive to the retina and uveal tissues.²⁴

Taken orally

The way that castor oil functions as a laxative is thought to be as follows: In the small intestine, pancreatic lipase enzymes release ricinoleic acid by hydrolyzing the oil.²⁵ That acid and its salts reduce absorption of water and electrolytes from the intestine. This is one of the main mechanisms of laxatives generally. Then the resulting build-up of fluid inside the small intestine stimulates peristalsis, which stimulates a bowel movement.²⁶ Fluctuations in pH in the small intestine also convert ricinoleic acid reversibly with sodium ricineolate, which induces contraction of the small intestine and the cecum.²⁷

Also, as castor oil activates EP3 receptors on the smooth muscle cells that line the GI tract, propulsive intestinal motility is stimulated.²⁷

If the laxative effect is very thorough or prolonged, then be careful to re-hydrate with water, as well as to replenish food and electrolytes after this process.

 

Side Effects and Contraindications

The castor bean itself is poisonous, and must never be eaten in any quantity at all, because of the protein ricin, which is a lectin that has been used in chemical warfare.  Ricin attaches to the red blood cells and causes them to lyse and to release free hemoglobin, a large protein which in enormous quantity, released from red blood cells, then overwhelms the urinary system, causing hemolytic uremia and then acute renal failure.²⁹ The cascade of damage is thoroughly described.³⁰

The oil that is extracted from the castor bean does not contain the water soluble ricin, and therefore the oil is non-toxic.  The oil may be taken internally in moderation.  Despite its reputation as a strong laxative, it does not have harsh effect, but rather stimulates peristalsis.

Castor oil taken orally in pregnancy increases prostaglandin E2, in the amniotic cells and placenta.³¹ It has been observed to induce uterine contraction and labor.³² Therefore, it should never be taken earlier in pregnancy than the expected time of delivery.  However, when it is taken at term, after premature rupture of membranes, it has been considered a safe and convenient way to induce labor.³³ 

When castor oil comprised 10% of the diet of rats, no toxic effects were found³⁴ and no growth retardation was observed in weanling rats on that diet.³⁵

 

Native Origin and Range

Castor is in the Euphorbiaceae family, considered to be from Africa or India, but long naturalized for millennia throughout the world.

Dr. Colleen Huber
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