Alpha lipoic acid is a sulphur-containing compound made in small amounts by the body and used by mitochondria as an enzyme cofactor. The strongest human evidence is in diabetic nerve pain, where 600 mg a day reduced symptom scores in randomised trials. In Great Britain it is sold as a food supplement, and no health claim for it is authorised.
That last sentence is the reason this article exists. On a British shelf, alpha lipoic acid sits beside vitamins whose boxes talk about energy and tiredness. Its own box says nothing, and legally it cannot, yet it has a larger randomised evidence base than most of what surrounds it. No page currently ranking for it in Britain explains that gap. This one sets out what the trials found, at what dose, with the awkward results left in.
What is alpha lipoic acid?
Alpha lipoic acid, also called thioctic acid or ALA, is a small fatty acid carrying two sulphur atoms. Your cells make a little of it, and it works inside mitochondria as a cofactor for the enzyme complexes that turn pyruvate and other fuels into usable energy, the same pathway NAD+ shuttles electrons through on the way to ATP.
Its second job is the one supplements are sold on. Oxidative stress is the state in which free radicals outrun the defences meant to contain them, and the cumulative damage that follows sits behind most antioxidant marketing. In the review by Shay and colleagues in Biochimica et Biophysica Acta in 2009, lipoic acid both scavenges free radicals directly and, more importantly, regenerates other antioxidants and shifts the cell’s own defences. Dissolving in both water and fat, it reaches compartments most antioxidants do not, which is why older writing calls it a universal antioxidant.
There is a catch that Shay and colleagues make explicit and that most consumer pages skip. The lipoic acid in food is covalently bound to protein and is not the same thing as the free lipoic acid in a capsule. The pharmacological effects described in the literature come from the free form, taken in quantities food does not supply.
R-alpha lipoic acid versus the standard racemic form
Alpha lipoic acid exists in two mirror-image forms, R and S. Only R occurs naturally in the body, and chemical synthesis produces an equal mixture of both, which is what capsules labelled simply alpha lipoic acid contain. R-alpha lipoic acid is sold separately at two or three times the price, on the argument that the natural form must work better.
The direct human evidence for that argument is one pilot study. Keith and colleagues, in Pharmacological Research in 2012, gave 500 mg of either R-lipoic acid or the racemic mixture to adults averaging 32 years and adults averaging 79 years, crossing them over after a washout. In older men, 2 out of 6 showed higher peak plasma levels and a larger area under the curve on the R form.
R-ALPHA LIPOIC ACID: THE PITCH AND THE DATA
WHAT THE MARKETING SAYS
- R is the natural form, so it must be better absorbed.
- The S half of the racemic mixture is inert filler you are paying for.
- A lower dose of R does the work of a higher dose of the standard form.
WHAT KEITH 2012 ACTUALLY FOUND
- A pilot study, six older men and a small young comparison group.
- Two of six older men absorbed R better. Not six of six.
- Young men tended in the opposite direction, favouring the racemic mixture.
- Absorption varied far more between older individuals than between the two forms.
- The authors conclude that age and individual variation should be considered, not that one form wins.
The practical reading is that the large randomised trials below were run with the racemic form at 600 mg. If you want the evidence base, that is what generated it. Nothing in the literature shows that a lower dose of R-alpha lipoic acid reproduces those results.
Diabetic nerve pain: where the real evidence is
Almost everything solid about alpha lipoic acid in people comes from one indication: diabetic distal symmetric polyneuropathy, the burning, stabbing, tingling and numbness in the feet that develops as a complication of long-standing diabetes.
SYDNEY 2: five weeks, and a clear symptom effect
Ziegler and colleagues published the SYDNEY 2 trial in Diabetes Care in 2006. It was multicentre, randomised, double-blind and placebo-controlled, with 181 patients in Russia and Israel taking 600 mg, 1 200 mg or 1 800 mg of oral alpha lipoic acid a day, or placebo, for five weeks after a one-week placebo run-in.
The primary outcome was the Total Symptom Score, which adds up stabbing pain, burning pain, pins and needles, and numbness in the feet. It fell by 4.9 points, or 51%, on 600 mg; 4.5 points, or 48%, on 1 200 mg; and 4.7 points, or 52%, on 1 800 mg. On placebo it fell 2.9 points, or 32%. All three doses beat placebo.
Total Symptom Score after five weeks, SYDNEY 2
Read the bars again. Tripling the dose bought nothing, while nausea, vomiting and vertigo rose with it. The authors concluded that 600 mg once a day gives the best risk-to-benefit ratio, and that is why 600 mg became the reference dose.
NATHAN 1: four years, and the result nobody quotes
Ziegler and colleagues then ran NATHAN 1, published in Diabetes Care in 2011: 460 patients with mild-to-moderate diabetic polyneuropathy randomised to 600 mg a day or placebo for four years. It is by a distance the longest trial of the compound.
The primary endpoint was not met. The composite of the Neuropathy Impairment Score for the lower limbs and seven neurophysiological tests showed no significant difference between groups, at p = 0.105.
Several secondary measures did favour alpha lipoic acid: the Neuropathy Impairment Score (p = 0.028), the lower-limb score and its muscular weakness subscore, with more patients meaningfully improved and fewer progressing. The authors explain the failed primary endpoint too. The placebo group barely deteriorated, so there was little progression left to prevent.
And one number that no consumer page reports. Serious adverse events were more common on alpha lipoic acid than on placebo, 38.1% against 28.0%, in a four-year trial of people with diabetes. Overall tolerability and dropout rates did not differ, but that gap belongs in any honest summary.
What the pooled evidence says
Hsieh and colleagues pooled ten randomised controlled trials covering 1 242 patients in Nutrients in 2023, restricted to oral alpha lipoic acid. Symptom scores improved with a dose-related trend, as did the neurological disability score and global satisfaction. Vibration perception threshold, nerve conduction and the lower-limb impairment score did not.
That shape is consistent across the literature: it moves what patients report, and not reliably what the nerve conduction machine measures. Pages that print only the first half are selling rather than reporting.
Why the same molecule is a prescription medicine in Germany
This is the context that makes the British situation intelligible. In Germany, thioctic acid at 600 mg is a licensed prescription medicine: Thioctacid 600 HR film tablets are indicated for the symptoms of diabetic polyneuropathy, taken as a single dose about thirty minutes before the first meal. In Great Britain the identical molecule is a food supplement you can buy without seeing anyone.
That difference explains a great deal. It is why the trials read like drug trials, with placebo run-in periods and neurophysiological endpoints. And it is why British information about it is so oddly thin, because the people selling it here are not allowed to describe the research.
authorised health claims for alpha lipoic acid on the Great Britain Nutrition and Health Claims Register, out of nine claims submitted
GB Nutrition and Health Claims Register, checked 30 August 2026. Claims on blood glucose, insulin sensitivity, protection of body lipids and protection of the nervous system are all listed as Non-authorised.
Nine separate claims for alpha lipoic acid appear on the register and every one of them is refused. It is the same silence a collagen tub has to keep, and for the same reason rather than for want of trials. The blood glucose and antioxidant claims trace back to EFSA opinion 2010;8(2):1474, the insulin sensitivity and nerve protection claims to 2011;9(6):2202. Since 1 January 2021 that register is the only list a supplement sold in England, Scotland or Wales may take health claims from. Northern Ireland continues to follow the EU list.
So a British brand may not tell you that alpha lipoic acid protects your nervous system, even though Ziegler and colleagues measured a 51% fall in symptom score at 600 mg. Refused is not disproved: the assessment was that the evidence did not establish cause and effect for a general population claim. But it is the line the label stays behind, and the silence on the box is legal rather than scientific.
Blood sugar, insulin sensitivity and weight
These are the three things most people search for after nerve pain, and the honest answers are smaller than the marketing.
Weight loss: two meta-analyses, two small numbers
Kucukgoncu and colleagues pooled ten randomised, double-blind, placebo-controlled studies in Obesity Reviews in 2017. Alpha lipoic acid produced 1.27 kg more weight loss than placebo, with a confidence interval of 0.25 to 2.29 kg, and a body mass index difference of 0.43 kg/m2. Dose made no difference in the meta-regression.
Namazi and colleagues pooled twelve trials in Clinical Nutrition the following year and found less: 0.69 kg of weight, and 0.38 kg/m2 of BMI. Waist circumference did not change significantly. Their conclusion is blunter than anything on a retailer’s page. Supplementation slightly but significantly decreased body weight and BMI, and it seems that alpha lipoic acid cannot be cost-effective.
Between 0.69 kg and 1.27 kg more than placebo, then: statistically real, clinically slight, over trials lasting weeks to months. If a product page implies alpha lipoic acid is a weight loss aid, that is the number it stands on.
Blood glucose
Both the glucose and the insulin sensitivity claims were assessed and refused. What is worth knowing practically is the direction: alpha lipoic acid tends to lower blood glucose rather than raise it, which is why it is not a neutral thing to add on top of diabetes medication. That belongs in the safety section rather than the benefits section.
What British shelves sell, and at what dose
The table sets the trial doses against what is on sale here. It describes the market and the literature, and it is not a recommendation. Doses are a matter for your GP or pharmacist.
| Form | Typical amount | What the evidence says |
|---|---|---|
| Racemic alpha lipoic acid, 600 mg | The dose in SYDNEY 2, NATHAN 1 and most pooled trials | The entire randomised evidence base was generated here. Higher doses did not work better and caused more nausea and vertigo. |
| Racemic alpha lipoic acid, 100 to 300 mg | The most common British retail strengths | Below the dose used in the trials. No trial supports a specific outcome at these amounts. |
| R-alpha lipoic acid | Often 100 to 300 mg, at a higher price | One pilot study in a handful of people. No trial has shown it reproduces the 600 mg racemic results at a lower dose. |
| Sodium R-lipoate and stabilised forms | Varies | Formulated for stability and absorption. No clinical outcome trial in this form. |
| Food: spinach, broccoli, offal | Micrograms, bound to protein | Not the same molecule as a capsule. Shay 2009 notes the free form is what produces the pharmacological effects. |
Two habits recur in the trial protocols: it is taken on an empty stomach, roughly half an hour before food, and as a single daily dose rather than split.
Side effects, including the serious one
The common effects are dose-dependent and unpleasant rather than dangerous. SYDNEY 2 recorded a clear dose-related rise in nausea, vomiting and vertigo, which is another reason the 1 800 mg arm was not worth its extra symptoms. Skin rash and, occasionally, a change in the smell of urine are also reported.
Insulin autoimmune syndrome
Insulin autoimmune syndrome, also called Hirata disease, is missing from every British page on alpha lipoic acid. It is a rare condition in which the body produces antibodies against its own insulin, causing severe hypoglycaemia in people who are not diabetic. Li and colleagues reviewed the published cases attributed to alpha lipoic acid in the Journal of Clinical Pharmacy and Therapeutics in 2021 and found 37 patients, 28 of them women, with a median age of 61.
The hypoglycaemic episodes struck at night or in the early morning in 60.7% of cases, in the late post-meal period in half, and after fasting in a third. Median blood glucose at onset was 2.19 mmol/L. Insulin measured at or above 100 microunits per millilitre in 94.6% of patients, and all 37 tested positive for IgG insulin autoantibodies.
The reassuring half: it resolves. Hypoglycaemia disappeared between five days and eight months after stopping alpha lipoic acid, with or without corticosteroids, the antibodies turned negative after a median of seven months, and follow-up found no recurrences.
Thirty-seven published cases worldwide is rare, and rare it should stay in your head. But if you take alpha lipoic acid and get episodes of sweating, shaking, confusion or palpitations at night or before breakfast, stop and see a GP, and say what you have been taking.
Who should not take alpha lipoic acid
| Situation | Why it matters |
|---|---|
| Taking insulin or any diabetes medicine | Alpha lipoic acid tends to lower blood glucose. Added to a medicine doing the same job, it can push you into hypoglycaemia. This needs your diabetes team, not a shelf. |
| Thyroid medicine | Levothyroxine absorption is sensitive to what else is in the stomach, and alpha lipoic acid is taken on an empty stomach at the same time of day. Ask your pharmacist about spacing. |
| Heavy alcohol use or suspected thiamine deficiency | Thiamine status and lipoic acid metabolism are linked in the same enzyme complexes. Deficiency should be assessed and corrected medically first. |
| Pregnancy and breastfeeding | No adequate safety data at supplement doses. |
| Children | Not studied. Accidental ingestion of high-dose capsules by young children has caused serious toxicity and is a medical emergency. |
| Unexplained hypoglycaemia, past or present | See the insulin autoimmune syndrome section above. |
One thing worth saying plainly, because most of the search traffic for this compound comes from people with burning or tingling feet. Those symptoms are not always diabetic neuropathy. Vitamin B12 deficiency, thyroid disease and compression in the lower back all produce them, and each has a different answer. That is a GP appointment before a supplement, and if the pain runs from the buttock down one leg it is a different question entirely.
If what you are managing is a persistent inflammatory background rather than nerve pain, the principle that governs alpha lipoic acid still applies: what reaches the blood decides everything, which is what a properly formulated bioavailable anti-inflammatory is built to solve. Neither is a treatment for a diagnosed condition.
Frequently asked questions
What is the main benefit of alpha lipoic acid?
The best-evidenced effect in humans is on the symptoms of diabetic nerve pain. In the SYDNEY 2 trial, 600 mg a day for five weeks cut the Total Symptom Score by 51%, against 32% on placebo, in 181 patients. Pooled trials show the same pattern: reported symptoms improve, nerve conduction measurements largely do not.
What are the negative side effects of alpha lipoic acid?
Nausea, vomiting and vertigo, all of which increased with dose in SYDNEY 2, plus skin rash and sometimes a change in the smell of urine. The serious one is insulin autoimmune syndrome, a rare cause of severe hypoglycaemia: 37 published cases, median age 61, which resolved after stopping the supplement.
Who should not take alpha lipoic acid?
Anyone taking insulin or diabetes medication without speaking to their diabetes team first, because it lowers blood glucose and the effects add up. Also anyone pregnant or breastfeeding, children, people with unexplained hypoglycaemia, and anyone with heavy alcohol use or suspected thiamine deficiency. Check with a pharmacist if you take levothyroxine.
Is alpha lipoic acid good to take every day?
The trials that produced the evidence used it daily and continuously: five weeks in SYDNEY 2, four years in NATHAN 1. Over those four years serious adverse events were more common on alpha lipoic acid than placebo, 38.1% against 28.0%. Whether daily use suits you is a question for your GP, not a general rule.
What should you avoid when taking alpha lipoic acid?
Food at the same time, since absorption falls with a meal, which is why trials dosed it about thirty minutes before breakfast. Alcohol, because heavy use depletes thiamine. And stacking it on top of diabetes medication or another glucose-lowering supplement without medical supervision.
Can I take vitamin B12 and alpha lipoic acid together?
There is no established interaction between the two, and products marketed for nerve symptoms often combine them. The point worth making is different: B12 deficiency is itself a cause of tingling and numbness in the feet, and it is diagnosed with a blood test, not guessed at with a supplement. Ask your GP to check.
Is R-alpha lipoic acid better than ordinary alpha lipoic acid?
R is the form your body makes, and standard capsules contain an equal mix of R and S. The direct human comparison is one pilot study: 2 of 6 older men absorbed R better, younger men tended the other way, and variation between individuals was larger than between the forms. The large trials all used the racemic form at 600 mg.
Sources
- Ziegler D., Ametov A., Barinov A., et al. Oral treatment with alpha-lipoic acid improves symptomatic diabetic polyneuropathy: the SYDNEY 2 trial. Diabetes Care, 2006. DOI: 10.2337/dc06-1216
- Ziegler D., Low P.A., Litchy W.J., et al. Efficacy and safety of antioxidant treatment with alpha-lipoic acid over 4 years in diabetic polyneuropathy: the NATHAN 1 trial. Diabetes Care, 2011. DOI: 10.2337/dc11-0503
- Hsieh R.Y., Huang I.C., Chen C., Sung J.Y. Effects of oral alpha-lipoic acid treatment on diabetic polyneuropathy: a meta-analysis and systematic review. Nutrients, 2023. DOI: 10.3390/nu15163634
- Li Z., Su Y., Yi D., et al. Analysis of the clinical characteristics of insulin autoimmune syndrome induced by alpha-lipoic acid. Journal of Clinical Pharmacy and Therapeutics, 2021. DOI: 10.1111/jcpt.13427
- Kucukgoncu S., Zhou E., Lucas K.B., Tek C. Alpha-lipoic acid as a supplementation for weight loss: results from a meta-analysis of randomized controlled trials. Obesity Reviews, 2017. DOI: 10.1111/obr.12528
- Namazi N., Larijani B., Azadbakht L. Alpha-lipoic acid supplement in obesity treatment: a systematic review and meta-analysis of clinical trials. Clinical Nutrition, 2018. DOI: 10.1016/j.clnu.2017.06.002
- Keith D.J., Butler J.A., Bemer B., et al. Age and gender dependent bioavailability of R- and R,S-alpha-lipoic acid: a pilot study. Pharmacological Research, 2012. DOI: 10.1016/j.phrs.2012.05.002
- Shay K.P., Moreau R.F., Smith E.J., Smith A.R., Hagen T.M. Alpha-lipoic acid as a dietary supplement: molecular mechanisms and therapeutic potential. Biochimica et Biophysica Acta, 2009. DOI: 10.1016/j.bbagen.2009.07.026
This article is general information, not medical advice. Food supplements do not replace a varied diet. Alpha lipoic acid is sold in Great Britain as a food supplement and no health claim for it is authorised. If you take insulin or any diabetes medicine, take levothyroxine, are pregnant or breastfeeding, or have nerve symptoms in your feet, speak to your GP or pharmacist before taking it.
