Caprylic acid

Caprylic acid (octanoic acid, 8:0, C8H16O2) is a saturated fat with eight carbons. FAO and WHO (the UN food and health agencies) class fatty acids with 8 to 13 carbons as medium-chain. That puts it with capric acid (10:0) and lauric acid (12:0) in the medium-chain group. The name comes from the Latin word for goat.

PubChem, a US chemical database, describes an oily liquid with a slightly unpleasant, rancid-like smell that occurs naturally in coconuts and breast milk. Most people meet it as a main ingredient of MCT oil (medium-chain triglyceride oil), which is why this page covers MCT oil too.

Medium-chain fats take a shortcut. FAO says they are absorbed across the gut and travel through the portal vein to the liver, where they are rapidly burned. Long-chain fats go out through the lymph instead.

Ketones are fuels the liver makes from fat. In a crossover trial in 9 healthy adults, pure C8 oil raised blood ketones more than coconut oil or any other test oil. The coconut oil peak was 25% of the C8 peak.

One more fact most readers do not know: your body attaches this 8-carbon fat to ghrelin, a hunger hormone made in the stomach. Ghrelin needs it to be active. In rats, though, eating more caprylic acid did not raise the active form.

The evidence is narrower than the interest. The best-supported use is the MCT ketogenic diet for children whose epilepsy drugs fail. It worked about as well as the classical diet in one randomized trial. A Cochrane review of ketogenic diets, though, rates the evidence low to very low.

For weight, a meta-analysis (a study that pools trials) found about half a kilogram. In Alzheimer’s disease, small trials, some tied to the makers, point to a benefit mainly in people without the APOE4 gene variant. For Candida we found lab studies only. Few trials test caprylic acid alone: most use MCT oil, a mix of C8 and C10, or tricaprilin.

Health benefits of caprylic acid

• ★★More seizure-free children on ketogenic dietsIn 13 trials, children on ketogenic diets, which include MCT diets, were 3.16 times as likely to be seizure free (low-certainty evidence). In one trial, the MCT diet controlled seizures about as well as the classical diet.
• ★★Slightly better thinking in memory declineIn people with mild cognitive impairment or Alzheimer’s, MCT supplements raised ketones, and a combined thinking measure improved clearly. In another analysis, general thinking improved but memory, language and attention did not.
• ★★A little less weight and waist sizeIn 749 healthy adults, swapping long-chain fats for C8 and C10 MCTs cut body weight by 0.51 kg more and waist size by 1.46 cm. The authors found commercial bias in the trials.
• ★★No overall LDL change, but higher triglyceridesAcross 7 trials, MCT oil barely moved LDL, the “bad” cholesterol (+0.02 mmol/L), but raised triglycerides by 0.14 mmol/L. Against oils rich in unsaturated fat, it raised LDL.
• ★★Less food eaten at later mealsIn a review of 17 studies (11 pooled for food intake), people ate less at later lab meals after MCT instead of long-chain fat. Appetite ratings and appetite hormones showed little change.

Foods high in caprylic acid

Caprylic acid is a minor fat in most foods. In our USDA ranking per serving, coconuts lead with 0.67 g in 1 oz (28 g). They are far ahead of semi-skimmed cow’s milk at 0.05 g in a cup (246 g), then buckwheat and cashews with traces.

Coconuts also lead per 100 g, at 2.35 g, and per 100 kcal. The ranking below shows the rest.

The richest everyday sources are oils, and the ranking does not include them. FAO lists dairy fat, coconut oil and palm kernel oil as the typical sources.

PubChem puts caprylic acid at about 8% of coconut oil, and a 2020 trial gives 6% to 8%. The coconut oil in a 2017 trial held 3%, so the share varies with the batch. PubChem gives cow’s milk fat an average of 0.79% of its fatty acids, in a range of 0.53% to 1.04%.

MCT oil is made by freeing caprylic and capric acid from coconut and palm kernel oil and joining them back to glycerol, according to FAO. It is a refined product and is not in our food data.

A daily 20 g of tricaprilin, as in the Alzheimer’s trial of AC-1202, carries about 18 g of caprylic acid. That is our arithmetic from the molecular weights.

At 0.67 g an ounce, that would take about 27 ounces (about 780 g) of coconut a day. At 0.05 g a cup, it would take about 370 cups of milk. Food gives milligrams to a gram or so, while the supplement trials use tens of grams.

How caprylic acid works

Most of what is known about how caprylic acid works comes from short human physiology studies, brain slices and animals. What it does for health is tested in the study cards above.

Five ideas cover it. It goes straight to the liver, and the liver turns it into ketones. C8 behaves differently from C10 and coconut oil, and it may act on nerve cells directly. The body also uses it to switch on ghrelin.

Here is each idea, and what has been seen in people.

It goes straight to the liver

After a meal, gut enzymes split fats. According to FAO, the short and medium-chain fatty acids released are absorbed across the gut. They travel through the portal vein to the liver, where they are rapidly burned. Long-chain fatty acids are rebuilt into fats, packed into chylomicrons (fat-carrying particles) and sent into the blood through the lymph.

A review of cell metabolism adds that medium-chain fatty acids enter mitochondria, the energy-making parts of cells, without the carnitine carrier that long-chain fats need.

For tricaprilin, a modeling study found that the steps before absorption limit the ketone supply. These are how well the oil disperses, how fast it is split and how fast the stomach empties. The step from octanoic acid to ketones played only a minor role in the model. Several authors are employees of the maker, Cerecin, which funded the study.

The liver turns it into ketones

Ketones are a fuel the brain can use when glucose is scarce. A crossover trial tested 15 healthy adults aged 65 to 73. Over 4 hours, 20 g of C8 lifted blood beta-hydroxybutyrate to a mean of 0.45 mmol/L. That compares with 0.18 with sunflower oil and 0.22 with 30 g of coconut oil, which was not clearly different from sunflower oil.

Carbohydrate gets in the way: 50 g of glucose cut the C8 value to 0.28 mmol/L. A German crossover study in 11 young women found the same pattern with tricaprylin at 0.2 g per kg of body weight. Ketones rose at low and medium glucose doses but not at the highest dose.

In people with Alzheimer’s disease, 30 g a day for one month doubled brain ketone use without changing brain glucose use. That held for a mix of caprylic acid (55%) and capric acid (35%) in 11 people, and for tricaprylin (95%) in 6 people.

C8, C10 and coconut oil are not the same

MCT oil is not one product. In the Quebec trial the classic MCT oil was 55% C8 and 35% C10. One test oil was over 95% C8, another over 95% C10, and the coconut oil held 3% C8 and 5% C10. Over 8 hours pure C8 was the most ketogenic, and the coconut oil peak was a quarter of it.

The rest of coconut oil is mostly other fats. FAO gives lauric acid at about 45 g per 100 g of coconut oil and palm kernel oil. Capric acid has its own page, because it behaves differently in the brain.

It may also act on nerve cells directly

Ketones were the first idea for how the MCT diet calms seizures, but ketone levels track seizure control poorly. In rat brain slices, decanoic acid (C10) blocked AMPA glutamate receptors and calmed seizure-like activity, and the ketones did not. In the same group’s earlier screen, octanoic acid at the same concentration had no effect on seizure-like discharges in brain slices. Decanoic acid had a strong one.

A 1986 study of children on the MCT emulsion diet found octanoic and decanoic acid in their blood. Their levels did not track seizure control. A 2018 review concludes that medium-chain fatty acids, rather than ketones, probably block seizure onset. It says they also change cell energy through mitochondrial biogenesis (making new mitochondria).

So in epilepsy, the benefit of the MCT diet may owe more to capric acid than to caprylic acid.

The body uses it to switch on ghrelin

Ghrelin, a hormone from the stomach, raises hunger. An enzyme called ghrelin O-acyltransferase (GOAT) attaches an 8-carbon fatty acid, octanoate, to ghrelin, and ghrelin needs that attachment to be active.

8 young men were sampled in the last 24 hours of a 61.5-hour fast. Most blood fatty acids were raised, but C8 and C10 were not. No fatty acid level predicted how much ghrelin was acylated, and the authors suggest the octanoate comes from inside the gut.

That raises the question of whether eating caprylic acid changes appetite. In rats it did not: dietary C8 left the active form of ghrelin unchanged and did not change body weight or food intake. In mice, an MCT diet raised plasma ghrelin 2.5-fold, yet ghrelin no longer made the mice eat more. We found no human trial that fed caprylic acid and measured active ghrelin.

What has been seen in people

The ketone rise is the best-established piece. It shows up in every crossover study above and can be seen in the brain with scans. What ketones do for health is less clear.

In epilepsy, the MCT diet matched the classical diet in one randomized trial. For weight, the effect is small, about half a kilogram in a meta-analysis, and the EFSA panel found the link not established. For thinking, the meta-analyses lean positive, mainly in people without the APOE4 variant. Yet healthy older adults saw no change, and a review of exercise studies found very little to no benefit from MCT oil for performance.

How much caprylic acid do you need?

No official body sets a daily amount of caprylic acid. The FDA has set no Daily Value for it, and the EU no Reference Intake.

The 2010 FAO and WHO report on fats names dairy fat, coconut oil and palm kernel oil as typical sources. It gives no intake value. PubChem lists it as a metabolite that the human body also makes, and we found no deficiency disease for it.

What trials have used is a different question. The MCT doses in the cards ranged from 17.3 g to 30 g a day, for weeks to months. The weight-loss trial used 18 to 24 g a day of MCT oil, and runners took 60 g a day.

The Alzheimer’s trial of tricaprilin used 20 g a day. The single-dose tremor trial used 4 mg/kg of octanoic acid, about 280 mg for a 70 kg adult (our arithmetic).

A 2021 review of the ketone response suggests starting with 5 g of C8 and building up to 15 to 20 g. Ideally, it says, take it after an overnight fast or with a low-carbohydrate meal. That is one team’s advice from the trials, not an official limit. A 2022 review of exercise studies calls 30 g the safe maximal dose for limiting side effects during exercise.

Forms of caprylic acid: absorption and effects

Caprylic acid reaches people in several forms. It is a small part of the fat in coconut oil, palm kernel oil and milk fat. It is in classic MCT oil (a mix of C8 and C10) and in C8 oil (tricaprylin, called tricaprilin as a drug). It also comes in emulsions, drinks and jellies, and tremor trials used the free acid.

The honest bottom line is that two trials compared C8 with coconut oil, and both found C8 raised ketones more. One found MCT oil more filling than coconut oil. We found no trial that compared a pure C8 oil with a C8 and C10 mix on a health outcome. So the claim that pure C8 is better for the brain or for weight has no trial behind it.

Two other popular claims need care. Coconut oil is not MCT oil, as the table and the cards below show. And MCT oil does not simply melt fat. In a trial of 24 overweight men, energy use was higher on day 2, but the difference was not clear by day 28.

The weight effects in meta-analyses are also small. No brands or product recommendations are made here.

Form	What it is	What studies show	Source
Coconut oil	The whole oil: high in lauric acid (about 45 g per 100 g) with a small share of caprylic acid (3% to 8%, depending on the source)	Its ketone rise was not different from sunflower oil in 15 older adults. It was less filling than MCT oil in a crossover study. In a meta-analysis of 16 trials it raised LDL cholesterol by 10.47 mg/dL compared with nontropical vegetable oils.	1, 2, 4, 5, 6
Classic MCT oil (C8 and C10)	Medium-chain triglycerides made from caprylic and capric acid; 55% C8 and 35% C10 in one trial	The form in most trials of weight, appetite and thinking. A meta-analysis of 13 trials found 0.51 kg less body weight than with long-chain fats. A mix of 55% caprylic and 35% capric acid at 30 g a day doubled brain ketone use in 11 people with Alzheimer’s disease. In 7 trials MCT oil left LDL cholesterol unchanged and raised triglycerides by 0.14 mmol/L. In 24 overweight men, energy expenditure was higher on day 2 but not significantly by day 28.	1, 3, 7, 8, 9, 10
C8 oil (tricaprylin or tricaprilin)	The triglyceride of caprylic acid, over 95% C8; sold as MCT oil or developed as the drug tricaprilin	The most ketogenic oil in an 8-hour crossover study, and 20 g lifted blood ketones to 0.45 mmol/L in older adults. Carbohydrate blunted the ketone rise in 11 young women. The product AC-1202 was tested in 152 people with Alzheimer’s disease, and tricaprilin in 8 infants with epileptic spasms. A model says the dispersion of the oil and stomach emptying limit its ketone supply.	3, 4, 11, 12, 13, 14
C10 oil (tricaprin)	The triglyceride of capric (decanoic) acid, over 95% C10	It was less ketogenic than C8 in the crossover study, where C8 was the most ketogenic oil. In the lab, decanoic acid rather than octanoic acid blocked AMPA receptors and calmed seizure-like activity in brain slices.	3, 15, 16
Free octanoic acid	The liquid acid, which PubChem lists as corrosive to metals and tissue	Taken by mouth only in tremor trials. A single 4 mg/kg dose did not beat placebo at the main time point in 19 people. A dose-escalation study with doses of 8 to 128 mg/kg reached no dose-limiting toxicity, with mild abdominal discomfort the most frequent side effect. In 16 people with voice tremor, 3 weeks of dosing lowered the magnitude of tremor against placebo.	2, 17, 18, 19
Emulsions, drinks and jellies	MCT mixed with water, milk or a gelling agent	The MCT emulsion diet was used in children with epilepsy, and giving food with the MCT reduced side effects. MCT jelly was tested for 30 days in Alzheimer’s disease. A review says emulsifying MCT might raise ketones and ease side effects. In 29 people, an MCT breakfast in liquid form lowered whole-day intake compared with a liquid long-chain fat and emptied from the stomach most slowly.	20, 21, 22, 23
MCT in infant formula	Preterm formula with 30% or more of its fat as MCT	In 10 trials, high-MCT and low-MCT formulas gave similar short-term growth, with low to very low certainty. One study reported more stomach and bowel intolerance with high-MCT formula.	24

Here are the form-specific and head-to-head studies, strongest evidence first, 4 in all.

Is caprylic acid safe? Supplements, dose and interactions

Caprylic acid at food amounts is not described as a safety concern in any source we found. The FDA lists it as a flavoring agent and adjuvant, limited to good manufacturing practice levels (21 CFR 184.1025). PubChem reports that JECFA, the FAO and WHO food additives committee, saw no safety concern at current intake as a flavoring.

We found no upper limit and no recommended intake for caprylic acid or MCT oil from the FDA, the EU or FAO and WHO. MCT oil and tricaprilin are another matter. The trials used tens of grams a day, for 14 days up to 6 months, so long-term safety at those doses is untested.

• Stomach and bowel upset is the main problem. In healthy older adults on 30 g a day of MCT, 75% in the main part had diarrhea and 11% withdrew because of side effects. In infants on tricaprilin, 75% had gut side effects and 50% vomited, while food eased side effects in children on the MCT diet. A 2021 review suggests starting with 5 g and building up, and says emulsifying the oil might ease side effects.
• Blood fats. A meta-analysis of 7 trials found that MCT oil did not change LDL cholesterol but raised triglycerides by 0.14 mmol/L. In 31 overweight adults who finished a 16-week plan, MCT oil did not worsen blood sugar, cholesterol or blood pressure compared with olive oil. Coconut oil is different: it raised LDL cholesterol by 10.47 mg/dL in a meta-analysis of 16 trials.
• Who should ask a doctor. A 1982 review lists ketosis, acidosis and cirrhosis as reasons not to use MCT, which raises ketones on purpose. People with liver disease, and anyone pregnant, breastfeeding or on medicines, should ask a doctor first. We found no trial in pregnancy or breastfeeding, and no human study of drug interactions.
• The pure acid. The liquid acid is corrosive to metals and tissue, according to PubChem, and it is not the form sold as MCT oil. In a tremor dose-escalation study, oral octanoic acid reached no dose-limiting toxicity up to 128 mg/kg in single doses. Mild belly discomfort was the most frequent side effect.
• Candida and other medical claims. Yeast claims rest on lab work: in dishes, octanoic acid blocked Candida albicans biofilm, and caprylic and capric acid blocked hyphae and biofilm (2017). An older study found capric acid killed the yeast fastest, but we found no human trial. In 2013 the FDA told the maker of Axona, a tricaprilin product, it was an unapproved new drug, not a medical food (RAPS). A phase 3 tricaprilin trial is registered, but its June 2026 record shows it had not started recruiting.

How to use caprylic acid wisely

• Count on food for small amounts only. An ounce of coconut gives 0.67 g and a cup of semi-skimmed milk 0.05 g in our USDA ranking. The supplement trials used 17.3 to 30 g a day of MCT. Food will not give you trial doses.
• If you try MCT oil, start low and take it with food. A 2021 review suggests 5 g to start, and children on the MCT diet had fewer side effects when they took it with food. Expect a modest result: about 0.51 kg of weight in a meta-analysis and no gain in endurance in 12 runners.
• Do not swap coconut oil for MCT oil. In 15 older adults, coconut oil did not raise ketones above sunflower oil. It was less filling than MCT oil in a crossover study. In a meta-analysis of 16 trials, it raised LDL cholesterol by 10.47 mg/dL.

History of caprylic acid

The name caprylic comes from the Latin word for goat, like caproic acid (6:0) and capric acid (10:0). PubChem lists two ways of making it commercially, both from coconut oil. They are saponification and distillation, or fermentation and fractional distillation of the oil’s volatile fatty acids.

The medical story starts with epilepsy. Fasting has been used for epilepsy since at least 500 BC, and doctors introduced the ketogenic diet in the 1920s to mimic it. In 1921 Wilder published two articles on ketonemia and epilepsy. Nine papers on the diet followed in the 1920s, covering more than 400 patients.

Antiseizure drugs then pushed the diet aside. In 1971 Huttenlocher and colleagues published medium-chain triglycerides as a therapy for intractable childhood epilepsy. In 1986 Sills and colleagues reported 50 children on the MCT emulsion diet, 8 of them seizure free. The first randomized trial of the classical and MCT versions came in 2009.

The brain-fuel idea reached Alzheimer’s disease in 2004. Reger and colleagues gave 20 people with Alzheimer’s or mild cognitive impairment an MCT drink and saw ketones rise. People without the APOE4 variant also did better on the ADAS-Cog test. In 2009 Henderson reported the 90-day trial of AC-1202, a tricaprylin product that its maker, Accera, planned to sell as Axona.

The FDA objected to its medical food status in 2013. A phase 3 trial of tricaprilin, called ALTER-AD, is registered with 535 planned participants. Its June 2026 record showed it was not yet recruiting.

Octanoic acid had a different path into medicine. The tremor trials began because 1-octanol, an 8-carbon alcohol, had shown benefit in essential tremor, and octanoic acid is its main breakdown product. A placebo-controlled trial of octanoic acid in essential tremor was published in 2013. In 2013 and 2016, UK lab work pointed to decanoic acid, rather than octanoic acid, as the seizure-calming fat of the MCT diet.

Frequently asked questions about caprylic acid

What is caprylic acid, and is it the same as MCT oil?

Caprylic acid is the 8-carbon fatty acid, called C8. MCT oil is a manufactured fat in which medium-chain fatty acids sit on glycerol, usually caprylic and capric acid. In one trial the classic MCT oil held 55% C8 and 35% C10, and the C8 oil over 95% C8. So caprylic acid is a main part of many MCT oils, and some products are almost pure C8.

Does caprylic acid kill Candida?

In dishes, to a degree; in people, we found no evidence. Octanoic acid cut Candida albicans biofilm formation by more than 75% at 2 µg/mL in a lab study. An older dish study found capric acid killed the yeast fastest.

We found no trial of caprylic acid by mouth for a yeast infection. A persistent infection needs a doctor’s diagnosis.

Is C8 better than coconut oil?

For raising ketones, yes in the two trials that compared them. In 9 healthy adults, the coconut oil ketone peak was a quarter of the C8 peak. In 15 older adults, 20 g of C8 lifted ketones to 0.45 mmol/L. Coconut oil (30 g) did not differ from sunflower oil.

The whole coconut oil raised LDL cholesterol by 10.47 mg/dL in a meta-analysis, while MCT oil left it unchanged.

Does MCT oil help you lose weight?

Only a little. A meta-analysis of 13 trials found 0.51 kg less body weight than with long-chain fats. In one 16-week plan, MCT oil gave a 1.67 kg lower weight than olive oil.

MCT lowered later food intake in lab meals but not hunger ratings. An EFSA panel concluded in 2011 that a cause and effect link between MCTs and weight loss was not established.

Does MCT oil help Alzheimer’s disease?

Possibly a little, mainly in people without the APOE4 variant. A meta-analysis of 9 publications found better general cognition. A 6-month trial in 52 people with mild cognitive impairment raised brain ketone use by 230%.

In healthy older adults, 30 g a day for 14 days raised ketones but did not change thinking. Tricaprilin is not an approved drug.

How much caprylic acid or MCT oil should I take?

No official dose exists. The trials used 17.3 to 30 g a day of MCT, and 18 to 24 g a day of MCT oil in the weight-loss trial. A 2021 review suggests starting with 5 g of C8 and building up to 15 to 20 g. Food gives far less: 0.67 g in an ounce of coconut.

What are the side effects of MCT oil?

Stomach and bowel upset is the main one. In healthy older adults on 30 g a day, 75% had diarrhea in the main part of the trial and 11% withdrew. MCT oil also raised triglycerides by 0.14 mmol/L in a meta-analysis of 7 trials. Taking it with food and building up slowly helps, and people with liver disease should ask a doctor first.

Does the MCT diet help epilepsy?

It helps some children, with low certainty. A Cochrane review of ketogenic diets, including the MCT diet, found children were about 3 times as likely to be seizure free (risk ratio 3.16). It rated the evidence low to very low.

In a trial of 145 children the MCT and classical diets worked about equally. It is a medical treatment for drug-resistant epilepsy, not a supplement to start on your own.