Benefits
Nerve comfort and nerve fiber support
Two 52-week placebo-controlled trials in 1,257 people with diabetic nerve damage found more sural nerve fibers, better vibration sense and, at 1,000 mg three times a day, less pain, but nerve conduction did not improve. A Cochrane review rated the pooled pain evidence very low certainty and noted maker funding. In women on taxane chemotherapy, 3 g a day worsened nerve symptoms.
Memory and thinking in older adults
A pooled analysis of trials in people with mild cognitive impairment or early Alzheimer's disease found a small advantage for 1.5 to 3 g a day over placebo. A review of 11 trials found better clinician global ratings at 12 and 24 weeks but no benefit on objective cognitive tests, and a 1-year trial of 3 g a day in 431 people found no slowing of decline.
Mood support
A pooled analysis of 12 randomized trials (791 participants, mean age 54) found that ALCAR reduced depressive symptoms compared with placebo or no treatment, most clearly in older adults. The trials were small and their results varied widely (I-squared 86%), and the authors called for larger trials. ALCAR is not a substitute for professional mental health care.
Energy and fatigue in older adults
In a double-blind trial in 96 adults over 70 with chronic fatigue, ALCAR lowered physical and mental fatigue scores versus a control group (dose not given in the abstract). In a placebo-controlled trial in people with hepatic encephalopathy, 2 g twice a day lowered fatigue scores. In women on chemotherapy, 3 g a day had no effect on fatigue.
Sperm motility (alone or with L-carnitine)
In two small trials (double-blind and placebo-controlled, 60 men each) in men with low sperm motility, 6 months of ALCAR increased sperm motility, most clearly in men with the lowest starting values. One gave 1 g with 2 g of L-carnitine; the other split the 60 men among four groups, one of which took 3 g of ALCAR alone. Both measured semen quality, not pregnancies.
Mechanism of action
Entry into the brain and acetylcholine building blocks
Oral and intravenous ALCAR raise its levels in the fluid around the brain, indicating that it crosses the blood-brain barrier, and its acetyl group can be used to make the messenger acetylcholine. This is a proposed mechanism; it does not show that ALCAR treats Alzheimer's disease.
Nerve growth factor signaling
Studies in rats found that ALCAR increased nerve growth factor levels in the brain, which may support nerve cell survival. This is offered as one explanation for the nerve fiber findings in diabetic nerve trials, but it has not been shown in people.
Mitochondrial fatty acid transport
Like L-carnitine, ALCAR helps move long-chain fatty acids into mitochondria for energy production, and laboratory work suggests it supports the making of proteins and cell membrane lipids.
Clinical trials
Analysis of two 52-week randomized placebo-controlled trials testing 500 or 1,000 mg three times a day (Sima et al. 2005, Diabetes Care)
1,257 intention-to-treat patients with established diabetic nerve damage.
Sural nerve fiber numbers and regenerating clusters increased and vibration perception improved in both studies. Nerve conduction velocities and amplitudes did not improve. Pain improved significantly in one study and in the combined group taking 1,000 mg.
Systematic review and meta-analysis of randomized trials comparing ALCAR with placebo, oral or intramuscular then oral (Li et al. 2015, PLoS One)
Four trials reported in three articles, 523 patients with diabetic or non-diabetic nerve pain.
Pain scores on a visual analog scale fell by 1.20 points more than placebo (95% CI 0.68 to 1.72); the oral-only subgroup showed 1.15 points. The effect was clearer in diabetic (1.47) than non-diabetic patients (0.71, borderline). Adverse event rates were similar to control. The authors called for larger, longer trials.
Cochrane systematic review of randomized trials of ALCAR against placebo or methylcobalamin (Rolim et al. 2019, Cochrane Database Syst Rev)
Four trials reported in three publications, 907 participants with diabetic peripheral nerve damage.
Against placebo, ALCAR lowered pain by 9.16 points on a 100 mm scale (three trials, 540 people), rated very low certainty; at 1,500 mg a day or less there was little difference. Two trials were funded by an ALCAR maker and the other two had a co-author who consulted for one. Safety evidence was too uncertain to judge.
Meta-analysis of double-blind placebo-controlled parallel trials of at least 3 months at 1.5 to 3.0 g a day (Montgomery et al. 2003, Int Clin Psychopharmacol)
People with mild cognitive impairment or mild Alzheimer's disease in trials lasting 3, 6 or 12 months.
ALCAR showed a small advantage over placebo on a combined summary measure (effect size 0.201) and on clinicians' global impression of change (0.32), seen from 3 months. ALCAR was well tolerated in all studies.
Cochrane systematic review of double-blind randomized placebo-controlled trials (Hudson et al. 2003, Cochrane Database Syst Rev)
11 trials, all in people with Alzheimer's disease.
More people improved on clinicians' global impression at 12 and 24 weeks, but not at 52 weeks, and there was no evidence of benefit on cognition, dementia severity or daily function. The reviewers said the positive result may be due to chance and found no evidence to recommend routine use.
Randomized, double-blind, placebo-controlled, parallel-group multicenter trial of 3 g a day (1 g three times a day) of ALCAR hydrochloride for 12 months (Thal et al. 1996, Neurology)
431 people aged 50 or older with mild to moderate probable Alzheimer's disease; 83% completed one year.
ALCAR and placebo groups declined at the same rate on both primary measures (ADAS cognitive score and Clinical Dementia Rating) and most secondary measures. A post hoc analysis hinted at slower decline in people aged 65 or younger. ALCAR was well tolerated.
Systematic review and meta-analysis of randomized trials of ALCAR alone or with antidepressants (Veronese et al. 2018, Psychosom Med)
12 trials with 791 participants (mean age 54, 65% women).
Across nine placebo or no-treatment controlled trials, ALCAR reduced depressive symptoms (standardized mean difference -1.10, 95% CI -1.65 to -0.56), with high heterogeneity (I-squared 86%). Benefits looked largest in older adults. The authors said larger trials are needed to confirm or refute the findings.
Randomized, double-blind trial (as indexed in PubMed) of ALCAR against a control group; the abstract gives neither the dose nor the comparison treatment (Malaguarnera et al. 2008, Arch Gerontol Geriatr)
96 people aged 71 to 88 meeting criteria for chronic fatigue.
Compared with the control group, ALCAR reduced physical fatigue, mental fatigue and fatigue severity scores and improved functional status and MMSE scores. A single trial in a specific older population.
Randomized, double-blind, placebo-controlled trial of 2 g ALCAR or placebo twice a day for 90 days, registered as NCT01223742 (Malaguarnera et al. 2011, Am J Clin Nutr)
121 people with mild (61) or moderate (60) overt hepatic encephalopathy, a liver-related brain condition.
In the mild group, ALCAR improved mental fatigue, fatigue severity, physical activity recall and a physical performance battery more than placebo; in the moderate group, fatigue severity and the 6-minute walk improved more. A specific patient population.
Placebo-controlled double-blind randomized trial: 2 months' washout, 6 months of 2 g L-carnitine plus 1 g ALCAR a day or placebo, then 2 months' follow-up (Lenzi et al. 2004, Fertil Steril)
60 infertile men aged 20 to 40 with low sperm motility; 56 completed.
Sperm parameters rose with treatment, and the clearest gains in forward and total motility were in men with the lowest starting motile sperm counts. A combination product, and pregnancies were not reported.
Placebo-controlled double-blind randomized trial: 1-month run-in, 6 months of 3 g L-carnitine, 3 g ALCAR, or 2 g L-carnitine plus 1 g ALCAR a day, or placebo, then 3 months' follow-up (Balercia et al. 2005, Fertil Steril)
60 infertile men aged 20 to 40 with low forward sperm motility; 59 completed.
Total and forward sperm motility rose in men given ALCAR, alone or with L-carnitine, and the antioxidant capacity of the semen increased. Men with lower starting motility were more likely to respond. The outcome was semen quality, not pregnancy.
24-week randomized double-blind placebo-controlled trial of 3,000 mg ALCAR a day in women receiving adjuvant taxane chemotherapy for breast cancer (Hershman et al. 2013, J Clin Oncol)
409 evaluable women (208 ALCAR, 201 placebo).
ALCAR did not prevent nerve symptoms at 12 weeks and made them worse by 24 weeks (neurotoxicity scores 1.8 points worse than placebo); grade 3 to 4 nerve toxicity occurred in 8 women on ALCAR versus 1 on placebo. Fatigue scores did not differ between groups.