Acetyl-L-carnitine

Acetyl-L-carnitine (ALCAR, also ALC or LAC) is L-carnitine with an acetyl group attached. It is the most abundant carnitine ester in the body [1] and is made in the brain, liver and kidney [8]. It is sold as a supplement for energy, mood and memory, and in some countries it is prescribed for cognitive impairment and diabetic neuropathy, with generic tablets of its own [2]. Much of the clinical record comes from trials run or supported by its Italian manufacturer, Sigma-Tau, from the 1980s onward [4][9].

Depression is where the evidence is most consistent. A 2018 meta-analysis of 12 randomized trials (791 people) found ALCAR reduced depressive symptoms against placebo or no treatment, matched antidepressants in three head-to-head trials with fewer side effects, and worked best in older adults. Most of the trials used 3 g a day for a median of eight weeks, the pool also included people with migraine, fibromyalgia and liver disease, and there was some evidence of publication bias [10]. A 2026 update pooled 10 trials (725 people) and reached the same overall conclusion. The effect was large in trials of older adults and small and non-significant in younger ones, and head-to-head and add-on trials showed smaller differences that were not significant. The trials were small, mostly old and European, very inconsistent with each other and showed signs of publication bias, and the authors judged the certainty low [3]. In a double-blind trial, 80 adults over 65 with dysthymia did as well on ALCAR 3 g a day as on fluoxetine 20 mg over six weeks, and fewer had side effects (6 of 41 against 18 of 39); two of the authors worked for Sigma-Tau [11]. In bipolar depression, ALCAR combined with alpha-lipoic acid for 12 weeks was no better than placebo [12]. Separately, people with major depression had lower blood ALCAR than matched controls at two independent centers, most of all those with treatment-resistant depression [13].

Cognitive decline is mixed. A 2003 meta-analysis of 21 trials in mild cognitive impairment and mild Alzheimer's disease (1,204 people analyzed), built partly on unpublished data from Sigma-Tau, the sponsor of most of them, found a small advantage over placebo [14]. The Cochrane review the same year found benefit only on clinicians' global impressions at 12 and 24 weeks, not at a year and not on any objective measure of cognition, severity or daily function, and said the positive result may be chance [9]. The two largest trials were negative: 431 people with Alzheimer's disease declined at the same rate on ALCAR 3 g a day or placebo over a year, and in a post hoc split those over 65 declined slightly faster on ALCAR [5]. A follow-up trial in 229 people with early-onset disease, the subgroup that had looked promising, also failed; only the completers showed less decline on one screening test, driven by its attention item [6]. Sigma-Tau funded both trials [5][6]. A small Korean trial in dementia with cerebrovascular disease improved one cognitive scale but no other outcome [15]. A 2017 Cochrane review found no eligible trial of ALCAR as a cognitive enhancer in healthy people; the only two that qualified used plain L-carnitine and found no effect [16].

Nerve damage. In diabetic neuropathy, two year-long trials co-authored by Sigma-Tau staff analyzed 1,257 patients. Nerve biopsies showed more fibers and regenerating clusters on 500 mg three times daily but not significantly on 1 g three times daily, vibration sense improved, and nerve conduction did not change. Pain was analyzed only in the 27% for whom it was the main symptom: it fell on 1 g three times daily in the North American trial and in the two trials pooled, but not in the European one [17]. The 2019 Cochrane review judged the pain benefit very uncertain and found it only above 1.5 g a day [4]. A broader meta-analysis of peripheral nerve pain found a moderate effect, larger in diabetic than in other neuropathy [18]. In HIV-related nerve damage, two weeks of injected ALCAR did not significantly reduce pain in the full intention-to-treat population, and did only after eight patients, seven of them taking antiepileptic drugs, were excluded [19], and it did not help nerves recover after carpal tunnel surgery [20]. The clearest result is a harm: in 409 women starting taxane chemotherapy for breast cancer, 3 g a day did not prevent nerve damage at 12 weeks and made it worse by 24 weeks [7], and the difference persisted over two years [21].

Fatigue and other uses. In a single-center trial in 96 people over 70 with fatigue, 2 g twice a day for six months reduced physical and mental fatigue and improved cognitive scores against placebo [22]. In multiple sclerosis fatigue it beat amantadine in a small crossover trial [23], though a Cochrane review found the evidence insufficient [24]. In an open-label chronic fatigue syndrome study it improved mental fatigue [25], and in fibromyalgia it reduced tender points, pain and depression against placebo by week 10 [26]. In cirrhosis with hepatic encephalopathy it lowered blood ammonia, but five small trials from a single team showed no clear effect on quality of life or fatigue [8]. Carnitines (L-carnitine alone or with ALCAR) improved sperm motility and shape in unexplained male infertility, but not pregnancy rates [27]. A psychiatric guideline task force did not recommend ALCAR for ADHD in children, after two trials found no benefit [28].

ALCAR carries two useful pieces. The carnitine part is needed to move long-chain fatty acids into mitochondria for burning, and the acetyl part can be passed on to keep acetyl-CoA levels up [29]. Beyond energy metabolism, it has been reported to affect brain phospholipid metabolism, neurotrophic factors, synapse structure and the release of several neurotransmitters [29]. Its acetyl group can feed acetylcholine synthesis, the original rationale for trying it in dementia [30]. It reaches the brain: in people with Alzheimer's disease, spinal fluid levels rose in step with blood levels after intravenous and oral dosing [31].

Epigenetic action on mGlu2. ALCAR can donate acetyl groups to histones, the proteins that package DNA, and mGlu2 receptors act as a brake on glutamate release [32]. In two rodent models of depression, daily injections of ALCAR acetylated histones at the gene for the mGlu2 receptor and raised mGlu2 levels in the hippocampus and prefrontal cortex. Antidepressant-like behavior appeared within 3 days, against 14 days for clomipramine, and lasted two weeks after the drug was stopped. The effect was absent in mice lacking mGlu2 [33]. The same induction of mGlu2 at nerve terminals is the proposed basis of ALCAR's pain-relieving effect in animal models of neuropathic and inflammatory pain [34].

Ammonia. ALCAR lowered blood ammonia in trials in cirrhosis [8], the basis of its use in hepatic encephalopathy.

ALCAR is usually sold as the hydrochloride: 590 mg of the salt carries 500 mg of ALCAR [7]. In a bioequivalence study of 590 mg tablets, a generic and a branded product both gave peak levels of about 1.7 µg/mL [2].

Absorption is poor. Laboratory studies suggest ALCAR is partly deacetylated in the gut wall, and the little that reaches the blood is quickly converted to carnitine; as of 2004 its bioavailability had never been measured in healthy people [1]. It shares its gut and kidney transporter with L-carnitine. In a 2025 study in healthy adults, single 0.5 g and 1.5 g doses raised blood ALCAR only slightly, with a peak at 4 hours. A 1.5 g dose of plain L-carnitine raised blood ALCAR as much as the same dose of ALCAR did, and raised blood carnitine more. Most of the ALCAR dose was not absorbed: gut bacteria broke it down to trimethylamine, which the liver converts to TMAO, and the authors estimated that under 5% of the dose was retained [35].

The figures in the table are from the same 2025 study [35].

ALCAR has been well tolerated in trials. In the dementia trials, adverse events were no more common than on placebo; the most frequent possibly drug-related ones were digestive, such as diarrhea, nausea and vomiting [9]. In the year-long Alzheimer's trial of 3 g a day, body odor was more common on ALCAR, and rash and increased appetite nearly so [5]. In the two year-long diabetic neuropathy trials no one stopped for safety reasons, and pain, tingling and oversensitivity were reported less often on 1 g three times daily than on placebo [17]. In a third year-long neuropathy trial, 4.1% stopped because of side effects (headache, facial tingling, digestive upset) against 1.4% on placebo, a difference that was not significant [4]. In depression trials, side effects were fewer than with antidepressants, and serious ones were rare and not attributed to ALCAR [3]. Taken with alpha-lipoic acid, it caused more diarrhea, foul-smelling urine and rash than placebo [12].

Chemotherapy neuropathy. ALCAR 3 g a day, started with taxane chemotherapy, increased nerve damage and reduced functional status at 24 weeks; eight women on ALCAR had grade 3–4 neuropathy against one on placebo [7]. The difference lasted two years [21], and a breast cancer guideline endorsed by ASCO recommends against ALCAR to prevent chemotherapy neuropathy because of possible harm [37].

TMAO. A single 1.5 g dose raised blood TMAO about twentyfold, to levels that have been linked to adverse health outcomes in earlier studies; whether TMAO itself causes cardiometabolic disease is unclear [35].

Thyroid hormone. Most of an ALCAR dose is converted to L-carnitine [35], and L-carnitine is a peripheral antagonist of thyroid hormone: 2–4 g a day reversed and prevented hyperthyroid symptoms in women taking suppressive doses of levothyroxine [39]. That is relevant to anyone taking thyroid hormone.

Chemotherapy. ALCAR worsened taxane neuropathy when taken during chemotherapy [7].

Kidney disease. Baseline blood carnitine and ALCAR levels were highest in people with poor kidney function, and urinary elimination tracked kidney function [38].