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.
Recommended Dose
500–1000 mg daily
Timing
Morning on empty stomach
Mechanism of Action
Crosses the BBB and donates acetyl groups for acetylcholine synthesis. Transports long-chain fatty acids into mitochondria for beta-oxidation. Supports neuronal energy metabolism and neuroprotection.
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.
Best Products
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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)
