Amino Acid
ALCAR (Acetyl-L-Carnitine)
Moderate EvidenceA 2003 meta-analysis of double-blind placebo-controlled trials in mild cognitive impairment and early Alzheimer's found a small but significant benefit (effect size 0.20). That is a clinical population at 1.5–3 g/day, not healthy adults at 500 mg — the everyday cognitive-enhancement case is extrapolated from it, not demonstrated by it. The wider record is less tidy than that one figure. A Cochrane review of 11 trials, all in Alzheimer's disease, found more people rated as improved on clinical global impression at 12 and 24 weeks but no benefit on cognition, dementia severity or daily function, and warned that the positive result may be chance (Hudson 2003). For mood, a meta-analysis of 12 randomised trials with 791 participants (mean age 54) found ALCAR reduced depressive symptoms against placebo and matched antidepressants in three head-to-head trials with fewer side effects — but the placebo-controlled results were highly inconsistent between trials and the authors asked for larger studies (Veronese 2018). And the largest randomised trial of all showed harm: in 409 women on taxane chemotherapy, 3 g a day for 24 weeks made nerve damage worse, still measurable two years later (Hershman 2018). Compared with citicoline and alpha-GPC, which supply choline, ALCAR supplies the acetyl side and its best evidence is on mood rather than memory; compared with CoQ10 it works on fuel transport rather than the electron-transport chain. Verdict: a plausible experiment for older adults with low mood, at the 1.5–3 g a day used in the trials rather than the 500 mg common in products — not a proven memory supplement, and never during taxane chemotherapy.
Recommended Dose
500–1000 mg daily
Timing
Morning on empty stomach
Mechanism of Action
Acetyl-L-carnitine (ALCAR) is carnitine carrying an acetyl group, and each half does a different job. The carnitine half transports long-chain fatty acids into mitochondria for beta-oxidation; the acetyl half can be used to maintain acetyl-CoA, the hub of cellular energy metabolism (Pettegrew 2000). Crosses the BBB and donates acetyl groups for acetylcholine synthesis. Reviews also describe effects on brain phospholipid metabolism, neurotrophic factors, synaptic structure and several neurotransmitter systems, most of it from laboratory work (Pettegrew 2000).
Side Effects & Safety
Mild fishy body odor, GI discomfort, or restlessness at high doses. May increase seizure frequency in susceptible individuals. Avoid with thyroid medication without supervision.
Do not use / talk to a doctor first
- Undergoing taxane-based chemotherapy — a randomised trial found ALCAR made nerve damage worse, not better
- Seizure disorder or on anticonvulsants
- Thyroid disease or on thyroid medication
- Pregnancy and breastfeeding — safety not established
Interactions
Taxane chemotherapy (paclitaxel, docetaxel)
Increased chemotherapy-induced peripheral neuropathy, still measurable two years later — the opposite of the intended effect
Source: Hershman 2018, JNCI (SWOG S0715)
Warfarin / acenocoumarol
Case reports of increased INR and bleeding risk
Source: NIH ODS carnitine fact sheet
Thyroid hormone medication
Carnitine can inhibit thyroid hormone entry into cells, potentially blunting treatment
Source: NIH ODS carnitine fact sheet
Pregnancy & breastfeeding
Not established. There is no adequate trial evidence for supplemental ALCAR in pregnancy or breastfeeding, so the honest answer is that we do not know — treat that as a reason to avoid it, not a reason to assume it is fine.
Who should avoid / see a doctor
Anyone receiving taxane chemotherapy, on warfarin, on thyroid medication, with a seizure disorder, or pregnant/breastfeeding. Stop and see a doctor if you develop new or worsening numbness, tingling or burning in the hands or feet.
Synergies
Used in These Stacks
See ALCAR (Acetyl-L-Carnitine) inside a full protocol — the stack pages cover when and why to combine it.
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References
- 1.Montgomery 2003, Int Clin Psychopharmacol — Meta-analysis of double-blind placebo-controlled trials (3–12 months, 1.5–3.0 g/day) in mild cognitive impairment and early Alzheimer's: significant advantage over placebo, integrated summary effect size 0.201 (95% CI 0.107–0.295) and CGI-Change 0.32 (95% CI 0.18–0.47). Benefit appeared by 3 months and grew over time. (clinical populations, not healthy adults; small effect size)
- 2.Hershman 2018, J Natl Cancer Inst — SWOG S0715: 409 women on adjuvant taxane chemotherapy, ALCAR 1000 mg three times daily vs placebo for 24 weeks. The ALCAR arm had significantly WORSE neuropathy scores (−1.39 points, 95% CI −2.48 to −0.30, P = .01), still evident at two years. This is the basis for the chemotherapy contraindication above. (randomised controlled trial showing HARM — reported here because a supplement page that only lists benefits is not an honest one)
- 3.Pettegrew 2000, Mol Psychiatry — Review: ALCAR contains carnitine and acetyl moieties; carnitine is important in fatty-acid beta-oxidation and the acetyl moiety can maintain acetyl-CoA levels; reported neurobiological effects include brain energy and phospholipid metabolism, neurotrophic factors, synaptic morphology and transmission. (narrative review)
- 4.Hudson 2003, Cochrane Database Syst Rev — Cochrane review of 11 double-blind randomised trials of ALCAR in Alzheimer's disease: more participants improved on Clinical Global Impression at 12 weeks (OR 2.33) and 24 weeks (OR 3.91) but not at 52 weeks; no evidence of benefit on cognition, dementia severity or functional ability; the significant result may be due to chance; no evidence to recommend routine use. (systematic review)
- 5.Veronese 2018, Psychosom Med — Meta-analysis of 12 RCTs (791 participants, mean age 54): ALCAR reduced depressive symptoms versus placebo/no intervention across nine trials (SMD −1.10, 95% CI −1.65 to −0.56, I² 86%) and was similar to antidepressants in three trials (SMD 0.06) with fewer adverse effects; most effective in older adults. (high heterogeneity; authors call for large trials)
