What it is
L-carnitine is a compound your body already makes and also gets from food, particularly red meat. It is not a peptide and not a hormone.
Its job is transport. Fat in the body travels as fatty acids, and those fatty acids have to get inside the mitochondria — the small structures inside your cells that turn fuel into usable energy — before they can be burned. They cannot cross into the mitochondria on their own. L-carnitine is the shuttle that carries them across.
That is why it shows up in almost every fat-loss formula on this site: it is an ingredient in Lipo-C, LIPO C+, and Lipo Shredder as well as being sold on its own.
It comes as a ready-mixed solution. Nothing is reconstituted. There are two quite different ways to use it.
The first injects it into a muscle — an intramuscular injection — at 500 to 1,000 mg at a time, a few times a week, for fat loss and performance.
The second injects it just under the skin — a subcutaneous injection — at much smaller daily doses that climb over 12 weeks, to build up the amount of carnitine stored inside muscle.
Both are set out below.
A quaternary ammonium compound, endogenously synthesised and dietarily acquired, whose primary role is mitochondrial transport: long-chain fatty acids cannot cross the inner mitochondrial membrane unassisted, and carnitine is the carrier in the carnitine shuttle that delivers them for β-oxidation. It is not a peptide.
Supplied as a ready-mixed solution; no reconstitution.
Carnitine is also a declared constituent of three lipotropic products on this site — Lipo-C, LIPO C+, and Lipo Shredder — at undisclosed quantities, which matters when stacking.
Two materially different protocols are in use, and both are given here.
The first is intramuscular in the glute or thigh (subcutaneous permitted but not preferred), 500–1,000 mg per injection, 1–5×/week, on an 8-week cycle with a 4–8 week washout, indicated for fat loss and performance.
The second is subcutaneous, 50–200 mg daily, titrated across a 12-week cycle with a 6–12 week washout, aimed at raising intramuscular carnitine stores.
The dose difference between them is an order of magnitude per administration. The concentration figures reconcile exactly, however — both protocols use 5 mg per insulin unit — so the two are the same product used two ways rather than two different preparations.
What it does
It moves fatty acids into the part of the cell that burns them. What you get out of that depends entirely on when you take it and what you take it with — this is the most useful thing to understand about it.
Fasted, in the morning or 30 to 60 minutes before cardio: more fat gets used as fuel. This is the fat-loss use.
With carbohydrates: the carnitine gets driven into muscle cells instead. That improves endurance and recovery, and builds up the muscle's capacity to burn fat later. This is the performance use.
So the same injection does two different jobs depending on the meal around it.
One practical point: absorption drops as the dose goes up. Splitting a dose gets more of it in than taking it all at once.
Mitochondrial long-chain fatty-acid transport for β-oxidation, with the downstream effect determined by substrate state at the time of administration — which is the organising principle of the dosing rather than an aside.
Fasted administration, morning or 30–60 minutes pre-cardio: increased fat oxidation. This is the lipolytic application.
Co-administration with carbohydrate: carnitine is driven intracellularly into muscle, improving endurance and recovery and building capacity for later fat oxidation. Insulin-mediated uptake is the mechanism. This is the ergogenic and carnitine-loading application.
The subcutaneous protocol frames the same split in its own terms: fasted 30–60 minutes pre-cardio for fat oxidation, endurance, or lipotropic protocols; with carbohydrate, a meal, or post-workout nutrition for intramuscular carnitine stores, athletic recovery, and long-term mitochondrial support.
Bioavailability falls at higher doses, which is the rationale for splitting — and the mechanistic reason the 12-week subcutaneous protocol runs 50–200 mg daily rather than 500–1,000 mg in a bolus.
Benefits
Evidence grades: what the labels mean
- Human trials Supported by randomised or placebo-controlled human trials.
- Limited human data Some human evidence, such as pilot studies, case reports or observational data, but no controlled trials.
- Animal or lab only Shown in animal or cell studies only; not yet tested in people.
- Anecdotal No published studies; based on user reports or theory.
Each grade reflects the strongest published support for that specific claim, not for the compound as a whole.
- Increases the amount of fat used as fuel, when taken fasted in the morning or before cardio.Anecdotal
- Improves endurance, when taken with carbohydrates.Human trials
- Improves recovery, when taken with carbohydrates.Limited human data
- Builds up the muscle's capacity to burn fat later, by raising the carnitine stored inside muscle cells.Human trials
- Supports mitochondria over the long term — the parts of your cells that produce energy.Anecdotal
- Supports athletic performance generally.Limited human data
- It is one of the ingredients in the lipotropic injections on this site, where it is credited with a direct role in fat use.Anecdotal
- Increased fat oxidation under fasted administration, morning or pre-cardio.Anecdotal
- Improved endurance when co-administered with carbohydrate.Human trials
- Improved recovery when co-administered with carbohydrate or post-workout nutrition.Limited human data
- Raised intramuscular carnitine stores, building capacity for subsequent fat oxidation.Human trials
- Long-term mitochondrial support — the stated aim of the 12-week subcutaneous protocol.Anecdotal
- Athletic performance enhancement, named as an indication alongside fat loss.Limited human data
- Declared constituent of the Lipo-C, LIPO C+, and Lipo Shredder formulations, credited there with a direct role in fat utilisation.Anecdotal
Reconstitution and dosing
There are two different protocols for L-carnitine. Both are below.
What is shared. The vial comes ready-mixed — nothing to reconstitute. Absorption drops as the dose gets bigger, so splitting doses gets more of it in. And the timing rule matters more than the dose: fasted, in the morning or 30 to 60 minutes before cardio, pushes it toward fat burning; taken with carbohydrates, it goes into muscle instead and improves endurance and recovery.
The intramuscular protocol. Inject into the glute or thigh. Subcutaneous — under the skin — is allowed but not preferred. A cycle is 8 weeks, followed by a 4 to 8 week break.
Standard, for fat loss and performance: 500 mg (100 units) per injection, 1 to 3 times a week.
Maximum: 500 to 1,000 mg (100 to 200 units) per injection, 3 to 5 times a week.
The subcutaneous protocol. Inject under the skin. A cycle is 12 weeks, followed by a 6 to 12 week break.
Weeks 1–2: 50 mg (10 units) once a day. Weeks 3–8: 100 mg (20 units) once a day. Weeks 9–12: 150 to 200 mg (30 to 40 units), either once a day or split between a morning and an evening dose.
The two are very different. The intramuscular one gives 500 to 1,000 mg in a single shot a few times a week. The subcutaneous one gives 50 to 200 mg every day. The daily-dosing one fits the warning that absorption falls at higher doses; the intramuscular one does not. Pick one protocol and follow it rather than mixing them.
About the numbers in the tables. Both protocols pair their millilitre doses with unit figures, and both use the same strength: 100 units is 500 mg, which is 5 mg per unit, or 500 mg in every millilitre. No vial size is specified. The tables use a placeholder vial of 5,000 mg in 10 mL, chosen because it gives that strength exactly. The vial size is a placeholder; the concentration is not.
Two protocols, given separately below.
Common ground. Ready-mixed solution, no reconstitution. Bioavailability declines at higher doses, which is the rationale for splitting. Substrate-state timing governs the effect: fasted, morning or 30–60 minutes pre-cardio, for fat oxidation; with carbohydrate, a meal, or post-workout nutrition, for intramuscular carnitine loading, recovery, and long-term mitochondrial support.
Intramuscular protocol. Glute or thigh; subcutaneous permitted but not preferred. Cycle 8 weeks with a 4–8 week washout. Best in the morning and/or 30–60 minutes pre-cardio.
Standard (fat loss / performance enhancement): 500 mg — 100 units — per injection, 1–3×/week.
Maximum: 500–1,000 mg — 100–200 units — per injection, 3–5×/week.
Subcutaneous protocol. Cycle 12 weeks with a 6–12 week washout.
Weeks 1–2: 50 mg (10 units) 1×/day. Weeks 3–8: 100 mg (20 units) 1×/day. Weeks 9–12: 150–200 mg (30–40 units), once daily or split into morning and evening doses.
Reconciliation. Per-administration doses differ by roughly an order of magnitude, and weekly totals by less than that — the maximum intramuscular protocol delivers 1.5–5 g/week, the subcutaneous titration 350 mg/week rising to 1.05–1.4 g/week. No rationale for the divergence has been established. The daily subcutaneous schedule is the one consistent with bioavailability falling at higher doses; the bolus intramuscular schedule is not. They should be run as alternatives, not combined.
Concentration basis and disclosure. Both protocols state unit-to-mass pairings, and both encode the same figure: 100 units = 500 mg in the intramuscular protocol, 10 units = 50 mg and 20 units = 100 mg and 30–40 units = 150–200 mg in the subcutaneous one. All four pairings resolve to 5 mg per insulin unit — 500 mg/mL. No vial volume or mass is specified, so the tables carry a derived placeholder of 5,000 mg in 10 mL, chosen because it reproduces 500 mg/mL exactly. The vial size is a placeholder; the concentration is fixed by both protocols.
Intramuscular — standard protocol (fat loss / performance enhancement)
Ready-mixed solution — nothing to reconstitute. Both protocols use 5 mg per insulin unit (500 mg/mL); no vial size is specified, so the 5,000 mg in 10 mL here is a placeholder chosen to reproduce that concentration exactly.
500 mg/mL · 5000 mcg per unit
Cycle: 8 weeks, then a 4–8 week washout · Frequency: 1–3×/week; intramuscular into the glute or thigh (subcutaneous allowed but not preferred); morning and/or 30–60 minutes before cardio
| When | Dose | Draw | How often |
|---|---|---|---|
| Standard dose (100 units) | 500 mg | 100 units | 1×/injection, 1–3 times per week |
Intramuscular — maximum protocol
Ready-mixed solution; no reconstitution. The 5,000 mg in 10 mL is a placeholder reproducing the 5 mg per insulin unit (500 mg/mL). Bioavailability falls at higher doses — the reason for splitting doses where possible.
500 mg/mL · 5000 mcg per unit
Cycle: 8 weeks, then a 4–8 week washout · Frequency: 3–5×/week; intramuscular into the glute or thigh; morning and/or 30–60 minutes before cardio
| When | Dose | Draw | How often |
|---|---|---|---|
| Low end of the range (100 units) | 500 mg | 100 units | 1×/injection, 3–5 times per week |
| Top of the range (200 units) | 1000 mg | 200 units(over 100 units: split across 2 syringes) | 1×/injection, 3–5 times per week |
Subcutaneous — 12-week titration
Ready-mixed solution; no reconstitution. The 5,000 mg in 10 mL is a placeholder reproducing the 5 mg per insulin unit that both protocols use. Per-dose figures here are roughly a tenth of the intramuscular protocol's — run one protocol or the other, not both.
500 mg/mL · 5000 mcg per unit
Cycle: 12 weeks, then a 6–12 week washout · Frequency: 1×/day, daily; subcutaneous; fasted 30–60 minutes before cardio for fat oxidation, or with carbohydrate for carnitine loading and recovery
| When | Dose | Draw | How often |
|---|---|---|---|
| Weeks 1–2 (10 units) | 50 mg | 10 units | 1×/day |
| Weeks 3–8 (20 units) | 100 mg | 20 units | 1×/day |
| Weeks 9–12 — low end (30 units) | 150 mg | 30 units | 1×/day, or daily total split between a morning and an evening dose |
| Weeks 9–12 — top of range (40 units) | 200 mg | 40 units | 1×/day, or daily total split between a morning and an evening dose |
5000 mg in 10 mL is 500 mg/mL, or 5000 mcg per unit. Draw 100 units (1 mL) for 500000 mcg.
Who should avoid it
- Anyone with cardiovascular disease.
- Anyone with a heart arrhythmia — an abnormal heart rhythm.
- Anyone with uncontrolled high blood pressure.
- Anyone sensitive to stimulants.
- Anyone with an anxiety or panic disorder.
- Anyone with epilepsy. L-carnitine may increase how often seizures happen.
- Anyone pregnant or breastfeeding.
- Interaction — use caution when stacking with caffeine or other stimulants.
- Interaction — L-carnitine can work against thyroid hormone activity and may reduce the effectiveness of thyroid replacement medication. It is used deliberately for that effect in people with an overactive thyroid.
- Interaction — there is an increased chance of low blood sugar when it is used with diabetes medicines such as insulin, metformin, and GLP-1 agonists (the class that includes semaglutide and tirzepatide).
- Interaction — using it with other fat metabolism agents or with stimulants may cause overstimulation, a faster heart rate, or jitteriness.
- Note: three of the lipotropic products on this site contain L-carnitine already, and two of those also contain stimulants. That combination is exactly what the interaction above warns about, inside a single vial.
- No separate contraindications or interactions have been documented for the 12-week subcutaneous protocol. Everything above applies to both protocols.
- Cardiovascular disease — contraindicated.
- Cardiac arrhythmia — contraindicated.
- Uncontrolled hypertension — contraindicated.
- Stimulant sensitivity — contraindicated.
- Anxiety or panic disorder — contraindicated.
- Epilepsy — contraindicated; it may increase seizure frequency.
- Pregnancy and lactation — contraindicated.
- Interaction: caution stacking with caffeine or other stimulants.
- Interaction: antagonism of thyroid hormone activity, potentially reducing the effectiveness of thyroid replacement. The same property is used therapeutically in hyperthyroidism, which is the mechanistic confirmation rather than a mitigation.
- Interaction: increased hypoglycaemia risk with insulin, metformin, and GLP-1 receptor agonists.
- Interaction: combination with other fat-metabolism agents or stimulants may produce overstimulation, tachycardia, or jitteriness.
- Lipo-C, LIPO C+, and Lipo Shredder all contain L-carnitine, and the latter two also contain sympathomimetics (Eria jarensis, albuterol). The overstimulation interaction above describes those formulations by construction. None of those formulations declares the carnitine quantity that would let the combined exposure be calculated.
- No separate contraindications, interactions, or adverse effects have been documented for the 12-week subcutaneous protocol. The set above is taken to govern both, since both concern the same compound.
- Note: the hypoglycaemia and the thyroid interactions both sit awkwardly against the fat-loss population most likely to use this, which overlaps heavily with GLP-1 users and with people on thyroid replacement.
Side effects
- Reaction where you inject — redness, swelling, burning.
- Nausea.
- Vomiting.
- Abdominal cramping.
- Diarrhoea.
- A fishy body odour, usually only at higher doses.
- Restlessness.
- Insomnia.
- Headache.
- Increased appetite, which is not common.
- Low blood sugar, particularly in diabetics and in anyone on insulin or other glucose-lowering drugs.
- It may increase how often seizures happen in people with epilepsy.
- Increased appetite is an odd finding on a fat-loss compound, though it is uncommon.
- Injection site reaction: erythema, swelling, burning.
- Nausea.
- Vomiting.
- Abdominal cramping.
- Diarrhoea.
- Fishy body odour, usually at higher doses — the trimethylamine effect.
- Restlessness.
- Insomnia.
- Headache.
- Increased appetite (uncommon).
- Hypoglycaemia, particularly in diabetics and those on insulin or glucose-lowering agents.
- May increase seizure frequency in epileptics.
- The fishy odour, the gastrointestinal cluster, and the reduced bioavailability at higher doses all point the same way, toward dose-splitting rather than bolus administration — which is what the 12-week subcutaneous protocol does and the intramuscular one does not.
- Appetite stimulation is an unexplained adverse effect on a compound indicated for fat loss.
User reports
User reports are individual experiences submitted by site visitors. They are not medical advice, are not verified for accuracy, and do not reflect Amino Reference's views. Read the evidence section above and talk to a clinician. Full disclaimer.
Stacking
Lipo-C already contains L-carnitine, alongside methionine, choline, and vitamin B5. Read it before adding standalone carnitine on top — you may be doubling up without knowing how much is already there.
Contains L-carnitine at an undeclared quantity alongside methionine, choline chloride, and dexpanthenol. Additive exposure cannot be quantified, which is the practical argument for choosing one or the other rather than stacking.
Also contains L-carnitine, and adds a stimulant. That is precisely the combination this page warns about — carnitine with stimulants can cause overstimulation, a fast heart rate, and jitteriness.
Carnitine plus Eria jarensis in one vial. This page's own interaction warning — fat-metabolism agents or stimulants combined with carnitine producing overstimulation, tachycardia, or jitteriness — describes that formulation exactly, at undeclared quantities.
Contains L-carnitine and albuterol, a stimulant. The same warning applies, more strongly.
Carnitine plus a β2-agonist in one vial. The strongest instance of the overstimulation interaction this page warns about, again at undeclared quantities.
Its entry names L-carnitine as a stack, for supporting the transport and burning of fatty acids while you are changing body composition.
Reciprocal suggestion from that compound's entry — carnitine supporting mitochondrial fatty-acid transport and oxidation during GH-driven recomposition.
Dosing figures have been reviewed and units are recomputed from the stated protocol.