Alpha-lipoic acid (ALA) is an antioxidant made in the body and available as a supplement. Its best evidence is for reducing the symptoms of diabetic peripheral neuropathy — burning, tingling and pain — where 600 mg a day, particularly by intravenous infusion, improved symptoms in several randomized trials and meta-analyses. Its effects on blood glucose and insulin sensitivity are small and inconsistent. It is generally well tolerated; it can lower glucose enough to matter alongside medication and can interfere with thyroid treatment.
What alpha-lipoic acid is
Alpha-lipoic acid (also called thioctic acid) is a sulphur-containing compound that the body makes in small amounts and uses as a cofactor for enzymes involved in turning nutrients into energy inside mitochondria. It is also a potent antioxidant that works in both water and fat, and it helps regenerate other antioxidants including vitamins C and E and glutathione.
Small amounts occur in spinach, broccoli, organ meats and yeast. Supplements provide far more than diet — typically 300–600 mg per capsule.
How it appears to work
In diabetic neuropathy, high glucose damages nerves partly through oxidative stress and reduced blood flow in the tiny vessels that supply them (see blood sugar and nerve health). Alpha-lipoic acid is thought to counter both: neutralizing reactive oxygen species and improving microcirculation to nerve tissue. Laboratory work also suggests it can improve glucose uptake into muscle, which is the basis of its use for blood sugar.
Evidence by use
| Use | Rating | What the trials show |
|---|---|---|
| Symptoms of diabetic peripheral neuropathy (intravenous) | Moderate | A meta-analysis of four placebo-controlled trials (1,258 patients) found that 600 mg per day by infusion for three weeks produced a clinically meaningful improvement in pain, burning and paraesthesia. |
| Symptoms of diabetic peripheral neuropathy (oral) | Limited | Oral doses of 600–1,800 mg per day for 3–5 weeks improved symptom scores in trials; a 2012 meta-analysis judged the oral effect statistically significant but of uncertain clinical relevance. Longer oral trials show slower progression of nerve deficits but not consistent symptom benefit. |
| Blood glucose / A1C | Limited | Small trials report modest reductions in fasting glucose and improvements in insulin sensitivity; results are inconsistent and effects small. |
| Weight | Insufficient | Minor reductions (around 1 kg) in some trials. |
| Diabetic retinopathy | Insufficient | A large trial of 600 mg daily did not prevent macular oedema. |
Alpha-lipoic acid is licensed as a prescription treatment for diabetic neuropathy in Germany and some other countries; in the United States, Canada, the United Kingdom and Australia it is sold as a supplement.
Doses studied
- Neuropathy: 600 mg per day is the standard dose, intravenous or oral. Higher oral doses (1,200–1,800 mg) did not add benefit and caused more nausea.
- Glucose: 300–1,200 mg per day in trials, without a clear dose–response.
Absorption is best on an empty stomach, 30–60 minutes before food.
Side effects
Generally well tolerated. Nausea, vomiting and stomach upset are the most common, particularly at doses above 600 mg. Skin rash and itching occur occasionally. A rare but serious reaction — insulin autoimmune syndrome, causing severe hypoglycemia — has been reported mainly in people of East Asian ancestry with a particular genetic makeup.
Interactions and cautions
- Glucose-lowering medication. ALA can lower blood glucose; combined with insulin or sulfonylureas it may cause hypoglycemia.
- Thyroid medication. ALA may reduce the conversion of thyroid hormone and interfere with levothyroxine; people on thyroid treatment should discuss it with their doctor.
- Chemotherapy. As an antioxidant it could theoretically interfere with some cancer treatments; oncologists generally advise against it during treatment.
- Thiamine deficiency. ALA can worsen thiamine deficiency, which is relevant in heavy alcohol use; thiamine is sometimes given alongside it.
- Pregnancy and breastfeeding: insufficient safety data.
Where it appears in supplements
ALA is sold alone (300–600 mg capsules) and appears in nerve support and blood sugar formulas. In nerve formulas, look for 600 mg per day; a product containing 50–100 mg is far below the amounts studied. See blood sugar supplement research.
Bottom line
If the question is nerve pain from diabetes, alpha-lipoic acid at 600 mg a day is one of the few supplements with reasonable trial evidence, and it is worth raising with the doctor managing your diabetes. If the question is blood glucose, the evidence is weak and other measures — weight, activity, medication — do far more. See the comparison of glucose-lowering ingredients.
Frequently asked questions
Does oral alpha-lipoic acid work as well as intravenous?
The clearest results come from intravenous trials. Oral trials at 600 mg or more per day also show symptom improvement, but reviewers have questioned whether the size of the oral effect is clinically meaningful. Oral ALA is what is available to most people, and it may help some.
Is R-lipoic acid better than regular ALA?
The R form is the one the body makes, and it is better absorbed than the mixture of R and S forms in standard supplements. Almost all the clinical trials used the standard racemic form, so the evidence is for that, not for R-lipoic acid specifically.
Does alpha-lipoic acid help with weight loss?
A few trials report small weight reductions (around 1 kg) at doses of 600–1,800 mg. The effect is minor and not a reason to take it.
References
- International Journal of Endocrinology. Alpha lipoic acid for symptomatic peripheral neuropathy in patients with diabetes: a meta-analysis of randomized controlled trials (2012). PubMed PMID 22331979. https://pubmed.ncbi.nlm.nih.gov/22331979/
- Diabetic Medicine. Treatment of symptomatic diabetic polyneuropathy with the antioxidant alpha-lipoic acid: a meta-analysis (2004). PubMed PMID 14984445. https://pubmed.ncbi.nlm.nih.gov/14984445/
- NIDDK. Diabetic Neuropathy (2023). https://www.niddk.nih.gov/health-information/diabetes/overview/preventing-problems/nerve-damage-diabetic-neuropathies
- National Center for Complementary and Integrative Health (NCCIH). Diabetes and Dietary Supplements: What You Need To Know (2021). https://www.nccih.nih.gov/health/diabetes-and-dietary-supplements-what-you-need-to-know
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