L-carnitine vs acetyl-L-carnitine

At a glance: L-carnitine vs acetyl-L-carnitine

Per gram, acetyl-L-carnitine hydrochloride contains about 673 mg of L-carnitine equivalent. A formulation therefore needs about 1.49 times more powder than with L-carnitine for the same carnitine-equivalent claim. L-carnitine is the free inner salt. Acetyl-L-carnitine hydrochloride is its acetyl ester, supplied as the hydrochloride salt.

Both dissolve readily in water and both take up moisture, which drives most handling decisions. Neither is a vitamin or a mineral. In EU food supplements their use therefore depends largely on national rules for other substances. For every carnitine form covered on this site, see the carnitine forms guide.

Content figures are for the pure substance, before assay adjustment.

Content per gram and label-claim arithmetic

The conversion uses the two molar masses. 239.69 ÷ 161.20 = 1.487, so 1.487 mg of acetyl-L-carnitine hydrochloride corresponds to 1 mg of L-carnitine. The inverse, 161.20 ÷ 239.69 = 0.6725, gives 67.3 % L-carnitine equivalent.

The arithmetic also works in reverse. Declaring 500 mg of acetyl-L-carnitine hydrochloride per serving means 336 mg of L-carnitine equivalent (500 × 0.6725).

These figures assume material at 100 % on the stated basis. For production, divide by the assay fraction on the certificate of analysis, then add any overage your stability data require. The overage calculator handles the second step.

Some brands declare acetyl-L-carnitine without the hydrochloride. That basis needs a different factor. Confirm the declared basis against the specification sheet before fixing label values.

Solubility, taste and processing

Moisture is the main processing issue for both forms. L-carnitine is markedly hygroscopic and can cake or liquefy in humid air. Acetyl-L-carnitine hydrochloride also picks up moisture. Weigh and blend both at low relative humidity, and keep opened containers sealed between uses.

In capsules, a hygroscopic fill can draw water from gelatin shells and leave them brittle. HPMC shells hold less water, which reduces this exchange. Run stability trials either way. The 1.49 mass factor matters here: at equal carnitine-equivalent claims, the hydrochloride may need a larger capsule or more capsules per serving.

For tablets, both forms usually need granulation or a dry-blend design that limits moisture contact. A glidant such as silicon dioxide helps flow in humid conditions. A moisture-barrier coating and tight packaging protect the finished tablet.

In powders and drinks, both forms dissolve quickly. Acetyl-L-carnitine is an ester, so it can hydrolyse in water to L-carnitine and acetic acid. Ready-to-drink liquids therefore need real-time stability data on acetyl-L-carnitine content. The hydrochloride makes aqueous solutions acidic and adds a sour note. That suits acidified drinks and effervescent systems. Check taste for both forms in the finished matrix.

EU regulatory status

Annexes I and II of Directive 2002/46/EC list permitted vitamins and minerals and their forms. Carnitine is neither, so neither form appears there. The Directive’s definition of food supplements still covers products containing other substances. The permitted forms guide explains how the annexes work.

No harmonised EU list sets which other substances may go into food supplements. Member states apply their own rules, notification procedures and, in some cases, maximum amounts. These differ between countries. Classification of a substance as food or medicine can also differ.

Regulation (EC) No 1925/2006 lets the Commission prohibit, restrict or place under scrutiny other substances through its Annex III. Check the current consolidated Annex III for both forms before launch.

Novel-food status must be confirmed for each form and use. See Regulation (EU) 2015/2283, the Union list in Implementing Regulation (EU) 2017/2470 and the novel food guide.

Labelling follows Regulation (EU) No 1169/2011 and the supplement-specific rules of Directive 2002/46/EC. The labelling guide covers both. For claim wording, consult the EU Register of nutrition and health claims and the health-claims guide.

Choosing between them

• Claim per unit. L-carnitine gives the most carnitine equivalent per milligram of fill. Choose it when capsule size or tablet mass is the limit.
• Product name. If the product is positioned on acetyl-L-carnitine, the ingredient list must name it. The mass factor then becomes a fixed design cost.
• Moisture control. Both forms need dry handling. L-carnitine is the more demanding of the two, which matters for sites without humidity-controlled weighing.
• Liquids. Ester hydrolysis makes acetyl-L-carnitine harder to keep on specification in ready-to-drink products. L-carnitine avoids that question.
• Markets. National treatment of each form can differ. Confirm status in every target member state before choosing.

Combining both forms makes sense when a brand wants both names on the label. It also works when a total carnitine-equivalent claim is split between forms to balance fill mass against positioning. Calculate each form’s contribution separately with the factors above. Declare each ingredient by its own name, and state the basis of any total. To price either form, or both, use the quote form.