Benefits according to published studies:
May be helpful in those with Alzheimer's disease. Acetyl l carnitine protects against amyloid-beta neurotoxicity. It acts as an antioxidant, stimulates neurotransmitter formation, and helps with alertness and improved concentration.

May benefit those with mental fatigue associated with chronic fatigue syndrome.

Patients with multiple sclerosis may benefit from acetyl carnitine, which could reduce their fatigue.

In aging rats, chronic supplementation increases cholinergic synaptic transmission and consequently enhances learning capacity. The memory of aging rats is rejuvenated by giving them a combination of acetyl l carnitine and alpha lipoic acid.

May benefit those with diabetic neuropathy. This nutrient could be helpful in chemotherapy induced peripheral neuropathy.

ADHD or ADD
L-acetylcarnitine may help with attention deficit hyperactivity disorder in children with the genetic disorder known as fragile X syndrome. Fragile X syndrome results from an inherited genetic defect on the X chromosome. It is associated with  mental retardation and may also cause autism and ADHD, ADHD is common in young boys with fragile X syndrome. Dr. Giovanni Neri from Universita Cattolica in Rome studied boys between 6 and 13 years old for a period one year. Twenty four received l-acetylcarnitine and 27 received placebo. There was a more effective reduction of hyperactivity and improvement of social behavior in treated patients. American Journal of Medical Genetics 2008.

Cataracts
The effect of acetyl-l-carnitine on lenticular calpain activity in prevention of selenite-induced cataractogenesis.
Exp Eye Res. 2008.
Results suggest that, in addition to its already-described antioxidant potential, it prevents selenite cataractogenesis by maintaining calpain activity at near normal levels.

For erectile dysfunction treatment, natural remedy for impotence
Acetyl-L-carnitine plus propionyl-L-carnitine improve efficacy of sildenafil in treatment of erectile dysfunction after bilateral nerve-sparing radical retropubic prostatectomy.
Urology. 2005.
These nutrients proved to be safe and reliable in improving the efficacy of sildenafil in restoring sexual potency after bilateral nerve-sparing radical retropubic prostatectomy.

Fibromyalgia
Double-blind, multicenter trial comparing acetyl l-carnitine with placebo in the treatment of fibromyalgia patients.
Clin Exp Rheumatol. 2007.
One hundred and two patients meeting the American College of Rheumatology criteria for fibromyalgia syndrome were randomized into the study. The treatment consisted of 2 capsules/day of 500 mg acetyl l-carnitine or placebo plus one intramuscular injection of either 500 mg acetyl l-carnitine or placebo for 2 weeks. During the following 8 weeks the patients took 3 capsules daily containing either 500 mg acetyl l-carnitine or placebo.  The "total myalgic score" and the number of positive tender points declined significantly and equally in both groups until the 6th week of treatment. At the 10th week both parameters remained unchanged in the placebo group but they continued to improve in the acetyl l-carnitine group with a statistically significant between-group difference.

MDMA use
Acetyl-l-carnitine provides effective in vivo neuroprotection over 3,4-methylenedioximethamphetamine-induced mitochondrial neurotoxicity in the adolescent rat brain.
Neuroscience. 2009 January.
3,4-Methylenedioximethamphetamine MDMA, ecstasy is a worldwide abused stimulant drug, with persistent neurotoxic effects and high prevalence among adolescents. The massive release of serotonin from pre-synaptic storage vesicles induced by MDMA followed by monoamine oxidase B (MAO-B) metabolism, significantly increases oxidative stress at the mitochondrial level. l-Carnitine and its ester, acetyl-l-carnitine (ALC), facilitate the transport of long chain free fatty acids across the mitochondrial membrane enhancing neuronal anti-oxidative defense. Here, we show the potential of acetyl l carnitine against the neurotoxic effects of MDMA exposure. The present work is the first to successfully demonstrate that pretreatment with ALC exerts effective neuroprotection against the MDMA-induced neurotoxicity at the mitochondrial level. These results indicate potential benefits of acetyl l carnitine application in the prevention and treatment of neurodegenerative disorders.

Methadone, opiate withdrawal
Acetyl-l-Carnitine in the Management of Pain During Methadone Withdrawal Syndrome.
Clin Neuropharmacol. 2008.
Thirty subjects meeting clinical criteria for methadone dependence were consecutively recruited and treated with acetyl-l-carnitine 2 g/d or placebo for a 3-week detoxification period. Acetyl-L-carnitine acted as an effective antihyperalgesic agent for relieving opiate-withdrawal hyperalgesia in animals and displayed clinical efficacy on other withdrawal symptoms such as muscular tension, muscular cramps, and insomnia.

Acetyl-L-carnitine in the management of pain during methadone withdrawal syndrome.
Clin Neuropharmacol. 2009.
This study was designed to determine the short-term effect of acetyl-l-carnitine (ALC) on symptoms of withdrawal in opiate-dependent subjects and animals and, in particular, on pain. Considering its tolerability, the excellent side effect profile, the absence of significant interactions, and the lack of abuse potential, ALC can be considered as a useful pharmacological adjunct in the treatment of opiate withdrawal.

Nerve growth, influence on the brain and nervous system
In animal studies, ALCAR protects nerve cells. It not only increases the number of regenerating nerve fibers but also morphologically improves the quality of regeneration and target organ reinnervation.

Sexual health, sex enhancement
I am wondering if Acetyl-l-carnitine has any negative sexual drive affect?
   Not that we are aware of. If anything, it should enhance sexuality.

Weight loss
High dosages of acetyl l carnitine may help reduce appetite, but a more effective product for appetite suppression and weight loss is Diet Rx.

Forms and different variations
You may come across other forms of N acetyl carnitine such as acetyl l carnitine arginate and propionyl l carnitine. We are not certain whether acetyl l carnitine arginate or other variants offer any advantages. As of 2010, we are not aware of human studies comparing the different forms. Acetyl l carnitine supplements work quite well to improve mental function, we are not sure if the arginate form adds any additional benefits.

Additional Forms
Acetyl L-Carnitine Hydrochloride
Galactarate
Arginate Dihydrochloride - As of December 2010, human studies with this supplement could not be found in medical journals.
Taurinate Hydrochloride,  Hydrogen Fumarate, L-Leucinate Hydrochloride, L-Ornithine Dihydrochloride
     There has not been enough research with each of these forms of ALCAR to determine which are best for long term human consumption.

Acetyl l carnitine and alpha lipoic acid
Some dietary supplements include a combination of these two nutrients. Although the combination of these two nutrients could be healthy, many acetyl l carnitine and alpha lipoic acid products have too high dosages of these nutrients and side effects could occur. We suggest using no more than 100 mg of ALCAR and no more than 20 mg of ALA when combining the two for long term use.

I have been a good customer of my local health food store over the years. I have purchased scores of vitamins / minerals/amino acids and herbs of all types. Mostly I buy herbs for energy as well as anti-oxidants to treat a rare disease that I have. I usually end up throwing away most of them after a couple of weeks use. However, I have been taking Alpha Lipoic Acid and Acetyl-l-carnitine  (500 mg) in the morning on an empty stomach for months now. My mind is clearer, my skin looks better, and my energy level is higher that it has been in years. It also affects my libido in a positive way. I do not work in the nutrition industry. Someone could argue this could be some sort of placebo effect, but it has been such a dramatic effect I don’t think that it is placebo effect at all.