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Castor oil has a reputation stretching back to ancient civilizations, serving everything from lamp fuel in Egypt to a household remedy in Europe. In the mid-20th century, scientists mapped out ways to modify natural castor oil to boost its usefulness in industry and medicine. By treating castor oil with hydrogen and adding chains of ethylene oxide, they crafted polyoxyethylene hydrogenated castor oil. This single innovation solved problems thick oils presented in industrial chemistry. The transformation led to what we now call RH40, which remains a backbone excipient in many pharmaceutical preparations. Its creation stands as an example of how persistent chemical tinkering leads not only to new molecules but shapes entire industries more efficient at drug delivery and safer compounds for daily use.
Polyoxyethylene hydrogenated castor oil, often called RH40, comes from hydrogenated castor oil that’s reacted with ethylene oxide. This process builds a heavier, water-soluble molecule. In the world of pharma, RH40 mainly acts as a solubilizer and emulsifier. It helps poorly soluble drugs dissolve in water-based systems, making effective oral solutions and liquid-filled capsules possible. I’ve seen its value in stabilizing vitamin prep and boosting the clarity of cough syrups, jobs it does invisibly every day. RH40 appears on ingredient lists under names like Cremophor RH40, Kolliphor RH40, and PEG-40 hydrogenated castor oil, making it a staple in labs that value safety records and predictability in their ingredients.
RH40 looks like a pale, almost waxy solid at lower temperatures, but it sweeps smoothly into a transparent, oily liquid above room temp. Its mild odor and near-neutral pH profile fit well with sensitive pharma applications, and a high hydrophilic-lipophilic balance (HLB) means it dissolves in water and sits well with lipophilic compounds. The average molecular weight usually falls between 2,000–3,000 Daltons. The ethylene oxide segments drive its solubility and help it form micelles—a feature that lets drugs ride through the body more efficiently. The product holds up across a wide pH span and shows strong chemical resilience under sterilization.
RH40 stands up to close scrutiny against BP, EP, and USP pharma grade benchmarks. Regulatory agencies set strict boundaries for ethylene oxide content, peroxide value, acid value, water content, and heavy metal limits. High-grade suppliers print precise details for identity, purity, and batch traceability on their labels. In the industry, a Certificate of Analysis (COA) always travels with every delivered drum, reflecting the level of oversight in pharma excipients. Tight labeling rules and specification checks give clinicians and pharmacists confidence in the safety of liquid-filled capsules and oral suspensions used in hospitals and clinics.
Making RH40 takes place in big, pressure-rated vessels where hydrogenated castor oil reacts with ethylene oxide. The hydrogenation step strips off any unsaturated bonds, creating a more stable base. Ethylene oxide then grafts onto this molecule, and operators can nudge the number of polyoxyethylene units to fit the desired HLB value. The process happens under nitrogen to protect against oxidation, with precise monitoring to keep impurities low. This work demands careful engineering, since ethylene oxide carries risks both as a chemical irritant and due to its explosive nature. Many experienced plant technicians recall days spent in protective gear, chasing the last traces of residual color or odor before a batch meets tight pharmaceutical specs.
After synthesis, RH40 can undergo further tweaks to suit special jobs. For instance, blending with other non-ionic surfactants tunes melting points and solubility for tricky drug formulations. Chemical derivatives expand possible uses; attaching functional groups or increasing ethoxylation creates specialty products for injectable drugs or high-load liquid systems. The molecule’s compatibility with a range of solvents, acids, and bases opens even more options for pharmaceutical scientists who want targeted drug delivery or improved patient tolerance.
Look for RH40 on pharmaceutical labels under synonyms like PEG-40 hydrogenated castor oil, Polyoxyl 40 Hydrogenated Castor Oil, Kolliphor RH40, and Cremophor RH40. Brand names often vary by supplier, each developed to meet regional pharmacopoeial standards. While some regulators still reference older synonyms, pharma manufacturing teams keep close track of approved names to avoid regulatory tripwires. Each synonym points to subtle differences, but at the core, the polyoxyethylene hydrogenated castor oil structure stays the same, bringing reliable performance batch-to-batch.
RH40 enjoys a solid acceptance from regulators around the globe. The compound ranks among the safest solubilizers in pharmaceutical excipients when handled with care. Food and drug administrations in Europe, the US, and Asia list RH40 as GRAS (Generally Recognized as Safe) for most uses, but batch testing for peroxides and free ethylene oxide remains a staple in pharma QA labs. Workers in production lines handle it with basic PPE and keep storage tanks closed off from air and moisture. Pharmacies and hospitals stock formulations with RH40 because its low toxicity profile—backed by decades of clinical experience—keeps patient reactions rare. Every year, regulatory agencies tighten allowed impurity thresholds and reinforce the need for real-time batch analytics.
Doctors and patients benefit from RH40’s unique properties every day, often without realizing it. Oral medicines, soft gelatin capsules, multivitamin syrups, and even some injectables call on RH40 to get water-insoluble active ingredients into a usable form. I’ve witnessed generic drug makers use it to broaden access to essential drugs in emerging markets, where solubility issues often stall cheaper products. Its role isn’t limited to medicines; RH40 also finds a spot in cosmetics, shampoos, and lotions, smoothing out product performance and stability. Its lack of taste and odor further expands its use in pediatric medicines, where acceptance among children is everything.
Scientists use RH40 as a platform to solve dissolving and stability puzzles in both new and reformulated drugs. Structure-activity studies examine its micellar encapsulation of active molecules, driving forward the search for less toxic and more efficient drug delivery systems. Universities and drug developers lean on RH40 to design self-emulsifying drug delivery systems (SEDDS) for next-generation treatments, especially biologics and poorly soluble new chemical entities. Several clinical trials turned up RH40’s ability to enhance oral absorption rates and minimize drug precipitation, opening new doors for disease treatments once limited by insolubility.
Large-scale toxicity testing paints a reassuring picture, although researchers keep a close watch on hypersensitivity reactions and rare cases of anaphylaxis, mainly in injectable formulations with high RH40 concentrations. Animal trials and long-term exposure studies show low risk of organ toxicity, mutation, or accumulation in the body. I’ve seen regulatory agencies, including the EMA and FDA, review case data and confirm that safety margins for oral, topical, and many parenteral uses stay well within acceptable ranges. Still, formulators choose the lowest functional concentrations, especially in therapies for sensitive groups like children, the elderly, or those with allergies.
The future for RH40 continues to look strong, particularly with its fit for increasingly complex molecules in pharma pipelines. Researchers push to further reduce impurity loads and tweak molecular tails for even gentler profiles. Green chemistry breakthroughs target more eco-friendly synthesis routes and better renewability of castor-based feedstocks. Drug designers keep flocking back to RH40, especially with rising pressure to develop medicines that dissolve faster and work better from the very first dose. If biopharma companies keep innovating, new versions of RH40 and its close relatives will show up in advanced therapies, patient-specific formulations, and even wearables that deliver drugs over long spans. The story of RH40 belongs not just to chemistry labs, but to millions of patients who depend on safe, predictable medicines.
Growing up, my grandmother always kept a bottle of old-fashioned castor oil in her medicine cabinet. It was her go-to solution for stubborn digestion or tired skin, but the story didn’t stop with simple home remedies. Polyoxyethylene hydrogenated castor oil—often called RH40—takes that same castor bean and transforms it using a combination of chemistry and modern needs. Through a process with hydrogen and ethylene oxide, chemists change crude castor oil into something water-loving, gentle, and effective for today’s medicines.
RH40 finds its spot in so many pharmaceuticals because it does what few ingredients can. It gets oily, hard-to-mix drugs to dissolve into water, making solutions clear and stable. Many modern drugs—think cyclosporine, some vitamins, and hormone therapies—come as sticky messes that water can’t handle alone. RH40’s job is to step in, break apart the stubborn oil globules, and keep medicines mixed up just right.
This kind of ingredient doesn’t only help the drug stay together; it helps your body take in the medicine as planned. I’ve seen patients struggle with chalky, hard-to-swallow pills or cloudy mixtures that never mix no matter how long they shake the bottle. RH40 gives pharmacists and drug makers an edge by keeping medications smooth, palatable, and ready for the body to absorb.
One of the reasons RH40 became popular is its track record with safety. It’s non-ionic, so it doesn’t irritate like some older surfactants. Most allergy-prone patients, kids, and folks taking new biologic therapies don’t deal with rashes or digestive troubles linked to this type of castor oil base. Hospitals pick it for intravenous solutions and eye drops, where harshness could do more harm than good.
I’ve watched doctors choose RH40-based formulas for children and for people who react to other emulsifiers. For instance, many eye drops for dry eyes or glaucoma patients contain RH40. The relief comes without burning or blurry vision, and compliance goes up because no one dreads every dose.
No ingredient works perfectly for everything. Some people can still have reactions, though rare, especially with high doses in injections. There are questions about long-term effects, especially as more new drugs combine unconventional ingredients. Since RH40 is made from castor oil and chemical processing, there’s room for improvement in sourcing and greener production. Right now, the industry leans on castor beans from areas facing environmental strain.
A possible answer involves developing similar surfactants from other sustainable plant oils or tweaking the process to reduce waste. Testing for new, even safer versions could mean more peace of mind for patients who take daily, lifelong medications.
Science keeps coming back to castor oil’s transformation for a simple reason: it works. As drugs become more complex and personalized, the need to safely combine oil-loving molecules with water keeps rising. Drug makers lean on RH40 for its blend of safety, reliability, and ability to help patients take their treatment without discomfort.
In my experience, it’s the everyday results—fewer side effects, easier dosing, less stress for families—that turn an ingredient into a trusted part of the pharmacy shelf. RH40 hasn’t replaced grandma’s old bottle, but it’s quietly doing its job in medicines people use every day.
Ask anyone involved in pharmaceutical production and they’ll tell you: choosing the right excipients can make or break a formulation. Rh40, also known as polyoxyl 40 hydrogenated castor oil, has become a staple in many drug products. This ingredient acts as a solubilizer, sometimes nudging tricky compounds into reliable, shelf-stable liquids or tablets. The catch? Not every batch is created the same, and small changes in quality can spell trouble down the road.
Pharmacopeias like BP (British Pharmacopoeia), EP (European Pharmacopoeia), and USP (United States Pharmacopeia) set strict guidelines for pharmaceutical ingredients. Their standards protect public health and keep products consistent from one bottle to the next. If Rh40 doesn’t tick every box, everything from stability to patient safety can be at risk.
I once worked in a lab where switching a single supplier led to delays — the product looked the same on paper, but failed USP’s impurity tests. Turns out, this sort of scenario pops up far too often. According to a 2022 survey from the Parenteral Drug Association, 17% of manufacturers reported batch rejections due to excipients falling short of compendial standards.
These pharmacopeias outline chemical identification tests, purity limits, microbial assessments, and labeling details. BP, EP, and USP all expect Rh40 to have a specific range of fatty acid esters, a validated method for measuring polyethylene glycol content, and tight control over possible impurities like free ethylene oxide. If a Rh40 supplier claims compliance, they should be able to present batch certificates showing each result matches or beats those pharmacopeial numbers.
Some regulatory agencies in Europe have flagged products because of missing or incomplete documentation. If the paperwork is lacking, health authorities don’t wait around — products get pulled or applications delayed. A review published by the European Medicines Agency cites non-compliance with Ph. Eur. standards as a leading cause for returned dossiers in 2021.
Sourcing compliant Rh40 starts with a deep dive into supplier credentials. Manufacturers serious about quality will request Certificates of Analysis (CoA) and ask to review the underlying lab data. One misstep I witnessed cost a company six months — a supplier claimed “USP grade” status, but couldn’t provide up-to-date microbial test reports. Communication with ingredients suppliers needs to be clear and direct, and regular audits keep everyone on their toes.
Some companies run in-house confirmation tests, even on “certified” batches. Gel permeation chromatography and peroxide value checks, for instance, catch impurities that slip past the supplier’s own testing. The value here comes from never assuming compliance just because a product landed on a truck with the right paperwork.
Missed compliance can’t just be chalked up to paperwork trouble. Weak oversight leads to recalls, regulatory warnings, or far worse — actual health risks. Health Canada’s 2023 annual report lists several cases where products missed excipient standards and landed on recall lists. The lesson is clear: without full compliance to BP, EP, and USP, Rh40 simply isn’t ready for responsible use in medicine.
With documented testing, open communication, and a healthy skepticism towards every batch that comes in the door, the risk stays low. Pharmaceutical production isn’t the place for shortcuts, not with ingredients that reach vulnerable patients every day.
Pharmaceutical manufacturers don’t cut corners with excipients, particularly those that go straight into the bloodstream or target sensitive tissues. Kolliphor RH40, widely known as Rh40, has found its niche as a reliable nonionic emulsifier, mainly built from hydrogenated castor oil and ethoxylated to a precise degree. It’s almost a silent partner in the drug formulation process, known for giving poorly soluble active ingredients a fighting chance.
The quality and make-up of Rh40 matter to researchers as much as the drug’s active molecules. Small changes in quality cascade through lab work, product stability, and safety. According to both the European Pharmacopoeia and typical manufacturer data sheets, key specifications tend to include:
The industry sees batch-to-batch consistency as a badge of honor. Well-run facilities will regularly post data close to the middle of the pharmacopoeial range. For example, the hydroxyl value may hover around 55 mg KOH/g, saponification value at 60 mg KOH/g, and water content at 0.5%. Labs across Asia, Europe, and the US often verify these readings, sharing results in open forums or industry roundtables.
Over years in pharmaceutical development, I’ve watched how small bumps in the acid value ripple into headaches with taste, stability, or even skin reactivity. Labs with tighter controls on these values end up fielding fewer questions from regulatory auditors and don’t scramble as often to repeat animal studies or scale up pilots.
Pharma grade certification draws a line between what’s safe for an ointment and what’s ready for an injectable or oral solution. Stray too far from the accepted hydroxyl range and partners start whispering about contamination. Elevated water or pH drift will turn a routine production run into an adventure, sometimes leaving a supply chain scrambling to make up for spoiled stock.
Even regulators pay close attention. In recent years, international health bodies have stepped up their focus on residual ethylene oxide, especially after contamination incidents in food and medical device sectors. Pharmaceutical sites with strong traceability and verifiable data on Rh40 keep projects moving smoothly across borders and inspection teams satisfied with their facts.
Sometimes, ingredient lots edge too close to their maximum or minimum cutoff and set off a series of checks. In these moments, I’ve seen teams pull together—the quality manager ships test samples to third-party labs, and the project manager keeps the communication lines open with formulation and procurement. In extreme cases of non-conformity, entire batches get set aside for investigation, a costly but necessary move to keep trust with prescribers and patients.
The solution starts with rigorous, transparent supply chain partnerships. Ongoing dialogue with excipient vendors pushes them to publish robust, easily-understood Certificates of Analysis. Active collaboration between quality assurance, formulation scientists, and regulatory staff drives continuous improvement, rather than chasing a perfect metric that only looks good on paper.
Rh40, often found in labs and manufacturing plants, helps keep things stable in products such as pharmaceuticals and cosmetics. Anyone working with it knows that attention to handling can make a real difference in results and safety. Over the years, I’ve seen colleagues run into issues just because a jug or drum of an ingredient got stored in the wrong place for a little too long. Those kinds of missteps can mean wasted money, lost time, and a risk to the final product’s quality.
Reliable storage starts with temperature. Rh40 does best in cool environments—somewhere between 20 and 25 degrees Celsius. Hot rooms or direct sunlight will speed up breakdown and might trigger unexpected changes to its properties. Light and humidity cause the same sort of headache. Shelving it in a dark, dry spot, away from windows and heating vents, protects both the product and the investment.
I remember a batch at a small compounding pharmacy where I worked, left too close to an old, draughty window. After a few months, the texture and appearance had changed enough that nobody could use it safely. That wasted batch cost a few hundred dollars and caused a week-long headache tracking down a replacement. Since then, we always check spots for leaks, heat sources, and drafts before using them for any raw material.
Once Rh40 gets exposed to air or moisture, the risk of contamination goes up. Opening a container and then failing to seal it tightly can introduce dust or even mold. I’ve seen how a handful of fingerprint smudges or a poorly closed cap can ruin an entire supply. Simple habits make a difference—clean gloves, dry scoops, and airtight seals let the material go the distance. Good storage isn’t just about keeping things organized; it’s about extending shelf life and avoiding costly mistakes.
Most suppliers will tell you that Rh40 stays stable for about two years if left unopened and given the right conditions. Cracking open a drum starts the clock ticking faster. Time, temperature swings, and repeated exposure all team up to eat away at that shelf life. I always write the opening date on the label. If the color or smell starts to change, or if there’s any sign of separation, it’s smarter to play it safe and dispose of the batch.
Trying to stretch an old ingredient usually backfires. In pharmaceutical and cosmetic work, using expired materials raises safety and regulatory concerns, so keeping a rotation log and tracking all batch dates can prevent expensive slip-ups.
It doesn’t take high-tech solutions. Clean, temperature-controlled rooms, sealed packaging, and trained staff go a long way. Avoiding cross-contamination is another must—keep Rh40 away from strong-smelling chemicals and reactive substances. Using smaller containers for frequent access helps limit how much of the material gets exposed each time.
In tighter spaces or smaller operations, simple tricks—like using a storage cabinet with desiccant packs and labeling everything clearly—help maintain order and safety. Large-scale users often rely on standard operating procedures and regular audits, which have helped several companies I consult for to cut down on product loss and customer complaints.
Experience shows that it’s easy to take storage for granted until something goes wrong. Small investments in good storage pay off. In my experience, the habit of checking storage conditions often, rotating stock, and training staff keeps Rh40 and any similar ingredient fresh, stable, and fit for purpose. Quality control starts the moment Rh40 arrives and only ends when the last drop goes into production.
Grab any pack of modern tablets or spot-check an intravenous solution, and you’ll likely come across names that sound more at home in a chemistry lab than on your nightstand. Rh40, also called Polyoxyl 40 Hydrogenated Castor Oil, tends to pop up. Drug manufacturers favor it for its power to blend water and oil in medications, which helps drugs absorb better, especially ones that don’t play well with water.
Safety isn’t based on a hunch, and drug ingredients aren’t picked by chance. Both the Food and Drug Administration (FDA) and the European Medicines Agency keep a close eye on substances like Rh40. Scientists have run toxicity tests on rats and other animals, looking for evidence of organ damage, changes in bloodwork, or unexpected weight loss. At the doses typically used in drug products, no red flags have stuck out. Drugs hitting the market featuring Rh40 have to pass safety checks, and that doesn’t come easy.
I’ve followed updates from regulatory panels and read through patient information sheets. Allergic reactions to Rh40 in medicines crop up very rarely. The most common side effect is mild digestive discomfort, usually only at high doses. Compare this to regular preservatives or colorants, which have much more concerning reputations, and Rh40 comes across as tame.
No chemical deserves a free pass. Even ingredients seen as safe benefit from scrutiny and long-term surveillance. A couple of years ago, doctors started watching more closely for PEG allergies, which share some chemical backbones with Rh40. So far, the evidence points to Rh40 being low-risk. It doesn’t bioaccumulate, and the kidneys clear it efficiently. Patients with a castor oil allergy might want to discuss alternatives, though, as there’s a tiny chance for cross-reactivity.
If people ask about “toxicity” in prescription ingredients, it usually comes from a place of anxiety or past bad experiences. Friends battling chronic diseases sometimes bring up long ingredient lists with questions. In all honesty, risks from Rh40 don’t match those of artificial dyes, parabens, or even certain antibiotics. Years of monitoring and controlled trials haven’t linked Rh40 to cancer, gene damage, or birth defects. It helps make vital drugs work better—like certain cancer therapies or anti-seizure medicines—by boosting how much medicine your body can use.
One area we could all improve is in open conversations between healthcare workers and patients. Ingredients like Rh40 can sound intimidating. Drug companies should provide easy-to-read safety data, not just pages of dense regulatory jargon. Pharmacists and doctors who break things down for their patients offer peace of mind and help people stick with their treatment.
It’s important to remember that nothing is entirely free from risk. People can develop sensitivities, even to ingredients considered safe. Still, the available evidence and decades of use make Rh40 a safe bet for most. If you have unusual symptoms and suspect a link, talk it over with your doctor—reporting reactions keeps the system safer for everyone.
| Names | |
| Preferred IUPAC name | Hydrogenated castor oil, ethoxylated |
| Other names |
PEG-40 Hydrogenated Castor Oil Polyoxyl 40 Hydrogenated Castor Oil Cremophor RH40 Macrogol Glycerol Hydroxystearate Hydrogenated Castor Oil Ethoxylate 40 Polyethylene Glycol 40 Hydrogenated Castor Oil |
| Pronunciation | /ˌpɒliˌɒksɪˌiːθɪliːn haɪˌdrɒdʒɪˈneɪtɪd ˈkæstər ɔɪl/ |
| Identifiers | |
| CAS Number | 61788-85-0 |
| Beilstein Reference | Beilstein Reference 969540 |
| ChEBI | CHEBI:86315 |
| ChEMBL | CHEMBL1201708 |
| ChemSpider | 37199707 |
| DrugBank | DB11097 |
| ECHA InfoCard | ECHA InfoCard: 07-2119485297-27-0000 |
| EC Number | 61788-85-0 |
| Gmelin Reference | 88445 |
| KEGG | C16111 |
| MeSH | Polyoxyethylenes; Castor Oil; Surfactants; Polyethylene Glycols |
| PubChem CID | 57420773 |
| RTECS number | WKJ3992879 |
| UNII | YGK4YUT8E5 |
| UN number | UN3082 |
| Properties | |
| Chemical formula | C₆₂H₁₂₂O₂₆ |
| Molar mass | ~2530 g/mol |
| Appearance | Clear, yellowish, viscous liquid |
| Odor | Characteristic |
| Density | 1.05 g/cm³ |
| Solubility in water | Soluble in water |
| log P | 2.4 |
| Vapor pressure | Negligible |
| Acidity (pKa) | ~4.5 |
| Basicity (pKb) | 12.5 |
| Magnetic susceptibility (χ) | -9.05 × 10⁻⁶ cm³/mol |
| Refractive index (nD) | 1.453 – 1.473 |
| Viscosity | 60–160 cP (25°C) |
| Dipole moment | 2.1–2.8 D |
| Thermochemistry | |
| Std molar entropy (S⦵298) | 185 J·mol⁻¹·K⁻¹ |
| Pharmacology | |
| ATC code | A06AG11 |
| Hazards | |
| Main hazards | Not a hazardous substance or mixture according to Regulation (EC) No. 1272/2008. |
| GHS labelling | GHS02, GHS07 |
| Pictograms | [GHS07, GHS09] |
| Signal word | Warning |
| Hazard statements | Not a hazardous substance or mixture according to Regulation (EC) No. 1272/2008. |
| Precautionary statements | P264, P270, P301+P312, P330, P501 |
| NFPA 704 (fire diamond) | 1-1-0 |
| Flash point | > 315°C |
| Autoignition temperature | 320°C |
| LD50 (median dose) | LD50 (median dose) of Polyoxyethylene Hydrogenated Castor Oil (Rh40) BP EP USP Pharma Grade: "≥ 5000 mg/kg (rat, oral) |
| NIOSH | ZE4850000 |
| PEL (Permissible) | PEL: Not established |
| REL (Recommended) | ≤ 10 |
| IDLH (Immediate danger) | Not established |
| Related compounds | |
| Related compounds |
Polyoxyethylene Castor Oil Polyoxyl 35 Castor Oil Cremophor RH40 Polyoxyethylene Glyceryl Triricinoleate Hydrogenated Castor Oil PEG-40 Hydrogenated Castor Oil Polyoxyl 40 Hydrogenated Castor Oil Cremophor RH60 |
Chengguan District, Lanzhou, Gansu, China
