Acetyl l-carnitine (ALCAR) is a modified form of carnitine, an amino acid derivative found in red meat, which is readily absorbed throughout the body, including the brain. It is involved in fatty acid metabolism and may improve several aspects of brain health, including mitochondrial function, activity of the neurotransmitter acetylcholine, and possibly cognition. However the data suggests that it does not provide a substantial cognitive benefit to patients with dementia.
Evidence from meta-analyses of randomized controlled trials suggests that ALCAR might slow cognitive decline, especially in patients with mild cognitive impairment (MCI) or the early stages of Alzheimer’s disease. However, the size of this effect is not likely to be large, and possibly not noticeable. Our search identified:
• 2 meta-analyses of randomized controlled trials in patients with MCI and/or Alzheimer's disease
• 2 clinical trials in elderly patients with fatigue
• Multiple small randomized controlled trials of ALCAR in MCI and/or Alzheimer's patients
• 2 observational studies of serum and cerebral spinal fluid (CSF) levels of carnitine
• 0 observational studies on the prevention of Alzheimer’s disease
• Many preclinical animal studies
ALCAR may improve cognitive function in elderly adults with fatigue based on two clinical trials from the same researchers , but no studies show that ALCAR can prevent Alzheimer's disease. Two studies reported that carnitine levels may decline in individuals as they progress to MCI and Alzheimer's disease .
Preclinical studies suggest many ways that ALCAR may benefit the brain. It may help to improve memory and mitochondrial function, especially in elderly animals . Evidence also suggests that it may raise the levels of nerve growth factor and increase the activity of acetylcholine, a neurotransmitter that is critical to healthy brain function and is substantially lost in Alzheimer's disease .
Little evidence exists on how carnitine treatment affects APOE4 positive or negative patients. One study reported that levels of l-carnitine in spinal fluid were lower in Alzheimer's patients without an APOE4 gene allele compared to patients with mild cognitive impairment . One preclinical study in mice reported that ALCAR and alpha lipoic acid treatment improved spatial and temporal memory tests but only in mice with APOE4 . For more information on what the APOE4 gene allele means for your health, read our APOE4 information page.
Despite some promise from early clinical trials, a meta-analysis of clinical trials concluded that ALCAR supplements are unlikely to provide a clinically meaningful benefit on the cognitive, behavioral, or functional abilities of Alzheimer's patients . For patients with less severe cognitive problems, specifically mild cognitive impairment or early-stage Alzheimer's disease, the clinical trial evidence is slightly more positive but also less reliable .
ALCAR is generally considered safe at doses up to 2–3 grams/day and has been used safely in clinical trials for up to 12 months. Some side effects noted in clinical trials include diarrhea, nausea, and vomiting . Carnitine can inhibit thyroid hormone activity, so those seeking treatment for hypothyroidism should not take any form of carnitine supplement . In addition, some research suggests that certain gut bacteria can convert carnitine to a substance called trimethylamine-N-oxide (TMAO), which may be associated with an increased risk of cardiovascular disease. However, this not well understood and needs more research .
NOTE: This is not a comprehensive safety evaluation or complete list of potentially harmful drug interactions. It is important to discuss safety issues with your physician before taking any new supplement or medication.
ALCAR is a common, over-the-counter supplement. Trials in Alzheimer's disease patients and elderly individuals with fatigue have generally used 2–3 grams/day for six months to one year. There are many natural sources of carnitine, such as red meat, fish, poultry, and some dairy products, but obtaining the doses used in previous clinical trials requires taking a dietary supplement.
For more information, visit the NIH's health information fact sheet.
More information on carnitine supplementation can be found at Drugs.com.