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Is Usnic Acid Safe?: The Side Effects

In the quest for a better physique, the right supplement can boost weight loss and help you achieve a more athletic, toned body.

Not all supplements are created equal though – for every high-quality product with well researched nutrients are ten more that use under-researched and potentially dangerous ingredients.

There are lots of options out there, and one of those is usnic acid. But is it safe? And what are the side effects?

In this article you’ll find out everything you need to know.

What is Usnic Acid?

First isolated in the 1800s, usnic acid (UA) is found pretty much exclusively in lichens [1] – a dual form algae and fungus organism. Occasional reports suggest it can also be found in kombucha tea, although this is currently unverified.

Under normal condition, this acid is yellow in color and has a bitter taste. It has antiviral and antimicrobial properties and as such is able to inhibit bacterial growth and infections [2]. For that reason it is used commonly used as either an active ingredient or preservative in healthcare and medicinal products such as creams, pastes and deodorants.

Over the last few years, usnic acid has been marketed as a herbal weight loss supplement. The small amount of manufacturers of the supplement claim that by taking it you can replicate the effects of exercise and increase metabolism. Subsequently, more and more people have chosen to supplement this compound to improve body composition either by using UA or its salt form sodium usniate. 

However, not only does research suggest that these claims are unverified, UA may also be unsafe.


Key Point: Usnic acid is found in lichen species. It is used commonly in antibacterial and antimicrobial products.

What are the Side Effects?

In isolated liver mitochondria, usnic acid was observed to directly inhibit and uncouple oxidative phosphorylation [3]. What this means is that your cells become less efficient with energy and subsequently, heat production increases. In theory this leads to an increase in metabolism.

The result of this though is that oxidative stress increases and subsequently damages hepatic tissue, leading to acute liver injury. 

A study published in The American Journal of Gastroenterology found that when used as a fat burner, usnic acid has a hepatotoxic effect which causes liver toxicity [4]. In some cases, patients developed fuminant hepatic failure – a more rapid acute liver failure.

Similarly, the Journal of Hepatology reported that a ‘surprising number’ of patients with severe liver damage had ingested usnic acid. Some individual case reports have even reported UA users needing liver transplants due to irreparable damage to liver tissue [5]. Some case studies have even reported deaths caused by the supplement [6].

Additional side effects include skin irritation and dermatitis when applied to the skin as a cream or cosmetic. In animal studies, it has been found to cause ataxia as well as hyperventilation and paralysis when eaten [7].

Key Point: Usnic acid is not a safe supplement. It can cause serious side effects including liver failure.

Is It Legal?

Since UA is classed as a herbal supplement, approval from the Food and Drug Administration (FDA) is not needed as such. However, they do strongly advise that it should be reviewed by the Office of Dietary Supplements due to it being potentially unsafe.

On top of that, the FDA issued a ‘Dear Healthcare Provider’ letter in 2001. The purpose of this type of letter is to alert physicians and other healthcare professionals about updated information or warnings about a drug. For them to issue a letter about UA suggests how unsafe it really is.



Usnic acid is a antimicrobial compound found almost exclusively in plant lichen. It is a yellow, bitter tasting extract that is used in a range of medicinal products.

Although it has previously been marketed as a fat burner, the FDA have concerns over its safety. There are a number of case studies and reports detailing the link between ingesting this supplement and acute liver failure. In more serious cases, there have been reports of complete liver failure, liver transplant and even death.

We strongly advise that you avoid this supplement and instead, consider using a fat burner that is safer and contains only well researched ingredients.

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  1. Ingólfsdóttir, K. Usnic acid. Phytochemistry. 2002; 61(7): 729-736
  2. Francolini, I et al. Usnic Acid, a Natural Antimicrobial Agent Able To Inhibit Bacterial Biofilm Formation on Polymer Surfaces. Antimicrob. Agents Chemother. 2004; 48(11): 4360-4365
  3. Han, D et al. Usnic acid-induced necrosis of cultured mouse hepatocytes: inhibition of mitochondrial function and oxidative stress. Biochem Pharmacol. 2004; 67(3): 439-51
  4. Durazo, FA et al. Fulminant Liver Failure Due to Usnic Acid for Weight LossFulminant Liver Failure. The American Journal of Gastroenterology. 2004; 99: 950-952
  5. Neff, GW et al. Severe hepatotoxicity associated with the use of weight loss diet supplements containing ma huang or usnic acid. J Hepatology. 2004; 41(6): 1062-1064
  6. Dailey, RN. Toxicity of Xanthoparmelia Chlorochroa and the Lichen Substance (+)-usnic Acid in Ruminants. 2008; ProQuest. ISBN 1109179928, 9781109179927
  7. Avigan, MI et al. Scientific and Regulatory Perspectives in Herbal and Dietary Supplement Associated Hepatotoxicity in the United States. Int J Mol Sci. 2016; 17(3)