Caprylic acid (C8): Evidence, Trial Doses & Interactions

About Caprylic acid (C8)

The eight-carbon medium-chain fatty acid, sold as a purified fraction of MCT oil. It is the most ketogenic of the medium-chain fats and the most expensive to isolate.

C8 is MCT oil with the slower-converting fractions removed, and the ketone data support the premium in a narrow sense: gram for gram, C8 raises blood beta-hydroxybutyrate more and faster than C10 or a mixed MCT. What is much less clear is whether a two- to three-hour rise in circulating ketones does anything useful in a person eating a normal diet. Trials of ketogenic medium-chain preparations in mild cognitive impairment have produced small effects in post-hoc subgroups, and the antifungal claims that circulate for caprylic acid rest on laboratory work rather than on any human trial.

Sold as

Liquid oil, Powder, Softgel

Standardised to

Percentage C8; products marketed as "C8" range from 60% to 99% pure — a product without this marker may not resemble what was studied.

Also known as

C8 MCT, Octanoic acid, Caprylic triglyceride

Regulation: Sold as a dietary supplement or food ingredient with no pre-market efficacy or safety review. Ketogenic medical foods containing caprylic triglyceride are regulated separately as medical foods in some markets.

What the research used

The amounts, forms and durations published trials of Caprylic acid (C8) actually administered.

These are the amounts published trials administered — not a recommendation, and not a dose to copy. Trial participants were screened, supervised and given a characterised preparation. What is in a retail bottle is frequently not what was studied, and the amount that suits one person is not general advice.

Studied for Raising blood ketones
10–30 g
Moderate
C8 oil, single dose · Acute, with beta-hydroxybutyrate peaking around 1–2 hours
Dose-dependent and reproducible. Higher doses raise ketones further but also raise the likelihood of cramping and diarrhoea, which is what limits the dose in practice.
Studied for Cognitive trials in mild cognitive impairment
20–30 g
Limited
Caprylic triglyceride daily · 3–6 months
Trials of a caprylic triglyceride medical food reported effects concentrated in participants without an APOE4 allele — a subgroup finding from a small trial, not a demonstrated result.

This is general information about food, not medical advice. It cannot diagnose, treat or replace guidance from a clinician who knows your history.

When it was taken

Each window says whether a trial compared it against an alternative, or whether it is convention and pharmacology. Most timing advice is the second kind.

Each timing below was actually compared against an alternative in a trial, which is unusual.

On an empty stomach
Moderate
The ketone rise is larger when C8 is taken without a carbohydrate-containing meal, because insulin suppresses ketogenesis. This has been measured directly. It is also the condition under which gastrointestinal side effects are worst, which is a real trade-off.
Timing was tested. A trial compared this window against another and reported a difference.

What each association actually rests on, and the papers behind it. A rating describes the state of the research, not how promising the supplement sounds. How we rate evidence.

Cognitive function

Brain & Cognitive Health

Limited evidence

Small trials of ketogenic medium-chain preparations in mild cognitive impairment report modest changes on some cognitive measures, largely in subgroups identified after the analysis. Trials in healthy adults have not shown consistent benefit.

What may be going on: C8 is rapidly converted to beta-hydroxybutyrate in the liver, providing an alternative brain fuel that does not depend on glucose transport or metabolism.

Limited evidence. Early human work, or mostly lab and animal research.

View the 2 sources

Changes in regional cerebral blood flow associated with a 45 day course of the ketogenic agent, caprylidene, in patients with mild to moderate Alzheimer's disease: Results of a randomized, double-blinded, pilot study.(opens in a new tab)
Randomised controlled trial · Experimental gerontology · 2018 · PMID 30006299
Supplementation of medium-chain triglycerides combined with docosahexaenoic acid improves cognitive function in Chinese older adults with mild cognitive impairment: A randomized double-blind, placebo-controlled trial.(opens in a new tab)
Randomised controlled trial · Journal of affective disorders · 2025 · PMID 40044083

Deep research mode adds each paper’s own conclusion and stated limitations.

Energy metabolism

Energy & Metabolism

Limited evidence

C8 reliably raises circulating ketones, which is a measurable metabolic change. Translating that into an effect on perceived energy, endurance or metabolic health has not been achieved in controlled trials.

Limited evidence. Early human work, or mostly lab and animal research.

View the 2 sources

Medium-chain triglycerides may improve memory in non-demented older adults: a systematic review of randomized controlled trials.(opens in a new tab)
Systematic review · BMC geriatrics · 2022 · PMID 36273115
Effect of medium-chain triglycerides and whey protein isolate preloads on glycaemia in type 2 diabetes: a randomized crossover study.(opens in a new tab)
Randomised controlled trial · The American journal of clinical nutrition · 2025 · PMID 39732398

Deep research mode adds each paper’s own conclusion and stated limitations.

Digestive comfort

Gut & Digestive Health

Not enough evidence

Caprylic acid is widely sold for gut yeast on the strength of its antifungal activity in culture. No controlled human trial has tested whether oral caprylic acid changes candida carriage or digestive symptoms, and most of it is absorbed in the upper small intestine.

Not enough evidence. Not enough human research to say anything useful yet.

View the 1 source

Effects of a motilin receptor agonist (ABT-229) on upper gastrointestinal symptoms in type 1 diabetes mellitus: a randomised, double blind, placebo controlled trial.(opens in a new tab)
Randomised controlled trial · Gut · 2001 · PMID 11511562

Deep research mode adds each paper’s own conclusion and stated limitations.

Things to know

Interactions, contraindications and dose limits, most serious first. Concentrated extracts interact with medication in ways the whole plant does not, so this section carries more weight here than it does on a food page.

Worth knowing
Ketoacidosis risk in diabetes
Interacts withSGLT2 inhibitors, insulin
Deliberately raising ketone production is not neutral in type 1 diabetes or alongside SGLT2 inhibitors, both of which carry their own ketoacidosis risk.
Worth knowing
Avoid in advanced liver disease
Medium-chain fatty acids are delivered directly to the liver by the portal vein. This is avoided in cirrhosis with encephalopathy and in other advanced hepatic disease.
Too much
Gastrointestinal intolerance
Cramping, urgency and diarrhoea are common and dose-related, and worse on an empty stomach — which is exactly the condition that maximises the ketone response. Starting at 5 g and building slowly is the usual approach.

Caprylic acid (C8)

What caprylic acid (c8) may help with

About Caprylic acid (C8)

What the research used

When it was taken

On an empty stomach

The evidence in depth

Cognitive function

Energy metabolism

Digestive comfort

Things to know

Ketoacidosis risk in diabetes

Avoid in advanced liver disease

Gastrointestinal intolerance

What caprylic acid (c8) may help with

About Caprylic acid (C8)

What the research used

When it was taken

⏳On an empty stomach

The evidence in depth

Cognitive function

Energy metabolism

Digestive comfort

Things to know

Ketoacidosis risk in diabetes

Avoid in advanced liver disease

Gastrointestinal intolerance

On an empty stomach