Alpha lipoic acid (ALA) is generally well tolerated at standard doses, but it does cause side effects in some people. The most common is nausea, which affects roughly 6% of people taking 1,200 mg per day. Side effects tend to be dose-dependent, meaning they become more likely and more noticeable as the dose increases.
Common Side Effects
The side effects most frequently reported with ALA are gastrointestinal: nausea, vomiting, and vertigo. Headache also occurs but is less common. All four of these follow a dose-dependent pattern. At 600 mg per day, most people experience no issues. At 1,200 mg and above, nausea becomes noticeably more frequent, and vomiting and dizziness follow the same trend.
These symptoms are typically mild and tend to improve if the dose is reduced. Taking ALA with food can also help minimize stomach upset, though some supplement labels recommend taking it on an empty stomach for better absorption. If nausea is a problem, splitting your daily dose across two or three smaller doses throughout the day is a practical workaround.
Blood Sugar Changes
ALA has a real, measurable effect on blood sugar. It increases the activity of glucose transporters in muscle cells, essentially helping your body pull sugar out of the bloodstream more efficiently. This is one reason it has been studied as a supplement for people with type 2 diabetes and insulin resistance.
But this same property means it can push blood sugar too low, especially if you’re already taking diabetes medication. The combination of ALA with insulin or oral blood sugar-lowering drugs can amplify the effect beyond what either would do alone. If you use diabetes medications, monitoring your blood sugar more closely after starting ALA is important, particularly during the first few weeks. Symptoms of low blood sugar include shakiness, sweating, confusion, and feeling lightheaded.
There have also been case reports of a rare condition called insulin autoimmune syndrome in people taking ALA. This occurs in genetically predisposed individuals (those carrying a specific immune system gene variant called HLA-DRB1*04:03) and involves the body producing antibodies against its own insulin, causing unpredictable drops in blood sugar. It’s uncommon but has been documented repeatedly over the past 15 years.
Interaction With Thiamine (Vitamin B1)
ALA and thiamine form a chemical complex when they interact in the body. Lab studies show the two molecules bind together in a 1:1 ratio, which could theoretically reduce the amount of free thiamine available for your body to use. For most people eating a balanced diet, this isn’t a concern. But for anyone already low in thiamine, such as people with chronic alcohol use, certain digestive conditions, or restrictive diets, long-term ALA supplementation could make a borderline deficiency worse. Ensuring adequate B1 intake while taking ALA is a reasonable precaution.
How Much Is Too Much
Doses between 600 and 1,800 mg per day have been used in clinical trials lasting up to six months and are considered safe for most adults. At least one study found that adults can take up to 2,400 mg without harmful effects, though higher doses don’t appear to offer additional benefits.
The picture changes at very high doses. Animal studies have identified a threshold of roughly 121 mg per kilogram of body weight per day (which, for a 150-pound person, would translate to over 8,000 mg) where liver enzyme changes and impaired liver function start to appear. No lethal dose has been established in humans, but these findings suggest that the liver is the organ most vulnerable to ALA overdose. Sticking within the studied range of 600 to 1,800 mg per day avoids this territory entirely.
For general antioxidant support, many people take 300 to 600 mg daily. Clinical trials for diabetic nerve pain have typically used 600 mg per day, which appears to offer the best balance of effectiveness and tolerability.
Use During Pregnancy
A retrospective study of 610 pregnant women who took 600 mg of ALA daily for at least seven weeks during pregnancy found no adverse effects in either the mothers or their newborns. The outcomes in the ALA group were comparable to, and in some measures slightly better than, those in the untreated control group. While this is reassuring, the evidence base is still limited. No large-scale prospective trials have been conducted, and data on ALA during breastfeeding remains sparse.
Who Should Be Cautious
Most healthy adults tolerate ALA without problems at doses up to 1,800 mg per day. The people most likely to run into issues fall into a few specific groups:
- People on diabetes medication: The blood sugar-lowering effect of ALA can stack with your existing treatment, raising the risk of hypoglycemia.
- People with low thiamine levels: ALA’s chemical interaction with vitamin B1 could worsen an existing deficiency over time.
- People taking very high doses: Side effects like nausea, vomiting, and dizziness increase predictably above 1,200 mg per day, and liver stress becomes a theoretical concern at extreme doses.
Starting at a lower dose, such as 300 to 600 mg, and increasing gradually gives your body time to adjust and makes it easier to identify whether any symptoms are related to the supplement.