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A Herx Reaction: When Feeling Bad Means You’re Getting Better

Written by Dr. Michael Ruscio, DC on August 16, 2025

Written by Dr. Michael Ruscio, DC on August 16, 2025 — Reviewed by Kellie Blake

• What Is a Herx Reaction?|
• Symptoms|
• A Positive Sign|
• How Long Does a Herx Last?|
• Herx vs Food Sensitivity|
• Herx or Allergy to Antimicrobial?|
• Ways to Ease a Herx|

What Is a Herx (Herxheimer) Reaction?

A Herxheimer reaction—often called a Herx—is a temporary inflammatory response to the rapid die-off of pathogens in the body. What that means is the treatment makes you feel worse, while actually working to make you better. Conventionally, it’s best known in relation to the use of antibiotics for treating specific infections, including syphilis, leptospirosis, tick-borne relapsing fever, louse-borne relapsing fever, and Lyme disease. 

In the functional health community, “Herx” has taken on a broader meaning, including similar reactions to treatments for chronic gut infections like SIBO, Candida, and dysbiosis. It’s also used in the context of treating vector-borne infections such as Bartonella and Babesia.

The Origins of the “Herx” Reaction 

The classic Jarisch-Herxheimer Reaction (JHR) is a set of symptoms starting within a few hours of antibiotic treatment for infections caused by Spirochetes bacteria, such as Treponema pallidum (the cause of syphilis) 1 2.

It was initially described by both Adolf Jarisch and Karl Herxheimer at the end of the 19th century 1. 

JHR symptoms include fever, chills, nausea and vomiting, headache, tachycardia (fast heartbeat), hypotension, and hyperventilation 1. The symptoms are stimulated by the release of toxic bacterial components into the bloodstream when the bacteria break apart 3 4 5.

These bacterial substances include lipoproteins and endotoxins, which cause a surge in inflammatory cytokines like tumor necrosis factor (TNF-α) and interleukin-6 3 5.

The JHR is considered a normal, self-limiting immune response—but in rare cases, it can be more serious, even mimicking sepsis 6. 

Importantly, a herx reaction is not to be confused with an allergic reaction to antibiotics like penicillin, doxycycline, or azithromycin. Instead, it’s a reaction to the infection itself being killed off.

What a Herx Reaction Means Now 

Now, the term Herxheimer reaction is used more broadly to denote any response that creates uncomfortable symptoms while being effective overall. These symptoms often appear during the treatment of chronic, low-grade infections or microbial imbalances, especially in the gut. 

We frequently observe these die-off reactions in clinical practice. They let us know that an antimicrobial protocol is working, but may also suggest that the body needs additional support to cope with the demands of detoxification.

Unlike the textbook JHR, which often lasts only 24 hours 1, Herx-like symptoms related to the treatment of gut dysbiosis or chronic low-grade bacterial, parasitic, or fungal infections may:

• Appear several days into treatment
• Last several days or even weeks
• Recur periodically, when treating infections that cycle between dormant and active phases 

This broader, experience-based perspective recognizes that not all Herx reactions follow the same predictable pattern, and many are milder but longer-lasting, especially when associated with gut pathogens.

For the rest of this article, I’ll be referring to the broader functional health definition of a Herx reaction, also called a die-off reaction.

Herx-Type Symptoms Related to Antimicrobial Use

Some of the most common die-off symptoms observed in our clinic include:

• Fatigue and low energy
• Brain fog or poor concentration
• Headaches
• Muscle or joint pain
• Flu-like symptoms (chills, mild fever, body aches)
• Gastrointestinal issues like nausea, bloating, diarrhea, or gas
• Skin rashes
• Mood changes, like depression 

While not every person experiences all of these, having many of them is not unusual during gut-based antimicrobial protocols or Lyme treatments.

Symptoms vary depending on the type of infection being treated and the individual’s ability to process the release of toxins.

A Herx Reaction Can Be a Positive Sign

Although die-off symptoms can feel uncomfortable, having a herx reaction is an encouraging sign that an antimicrobial protocol is successfully eliminating pathogens.

During a herx reaction, the immune system is activated as the body works hard to clear the bacterial byproducts and other inflammatory molecules 3 5. This provokes some challenging symptoms, but suggests the treatment is addressing the root cause of the imbalance.

Framing symptoms as a constructive step in your healing journey can be psychologically helpful.

That said, a significant die-off reaction can also be a signal that detoxification pathways need more support—more on this below. 

How Long Do Herx Symptoms Last?

In my clinical experience, most die-off symptoms start 2-5 days after beginning antimicrobial treatment. 

• For gut-related infections like small intestinal bacteria overgrowth (SIBO) or Candida, symptoms usually last 1–4 days, although occasionally they can last up to 4 weeks.
• With vector-borne illnesses, like Babesia, reactions tend to come and go over a longer period. Symptoms may go away, then return weeks later, depending on the activity of the infection.

The wave-like symptom pattern happens because some vector-borne infections exist in two forms—growing and dormant. Initially, die-off occurs as growing microbes are killed. Later, as dormant microbes become active, another wave of die-off may occur.

Herx Reaction vs. Food Sensitivity

Many clients report feeling like their symptoms are triggered by foods—especially those high in FODMAPs, histamine, sulfur, or oxalates.

In reality, the treatment of underlying vector-borne infection leading to cyclical Herx flares may be the main issue.

Unless there is a clear, consistent pattern between eating a specific food and experiencing a reaction, it’s more likely that a chronic infection is going through periods of activity and dormancy, causing symptoms to come and go. 

Am I Allergic to an Antimicrobial or Having a Herx Reaction?

People react differently to different treatments, and occasionally a client may have an adverse reaction (allergy or intolerance) to a specific antimicrobial.

A key way we differentiate between a Herx reaction and an allergy or intolerance to a specific antimicrobial treatment or supplement (e.g., antimicrobial herb like oregano) is through timing:

If you suspect you are reacting to the antimicrobial treatment, the next step is to explore alternative treatments. For example, if you have an intolerance to oregano, you may consider trying a different antimicrobial herb, like artemisinin. Consulting with a qualified medical professional can be helpful in finding out what is best for your unique needs. 

Ways to Ease a Herx Reaction

A Herx reaction can feel discouraging, but there are effective ways to minimize discomfort, support your body’s detoxification systems, and continue healing.

However, it’s important to listen to your body and assess whether you feel able to continue with the protocol.

If you have concerns or are unsure about any symptoms you’re having, please consult with your doctor to determine the best course of action.

Before Starting Treatment

When we have clients with a history of food or supplement reactivity, starting with a full dose of an antimicrobial might trigger stronger die-off symptoms. To ease into treatment, we start with ½ or ¼ of the recommended dose and then slowly increase the dose every 3–7 days.

Once you have begun treatment, anti-inflammatory and detoxification support can help ease Herx symptoms. In the clinic, we typically recommend that our clients try one to two support methods from each of the categories below. 

Anti-Inflammatory Support

• Curcumin: 2–3 capsules, twice daily
• Quercetin: 2–3 capsules, twice daily
• Homemade “Alka Seltzer” (for digestive discomfort): Mix ½ tsp potassium bicarbonate + ¼ tsp baking soda in water
• Lemon water: Squeeze 2 lemons into water and sip over 1 hour 

Detoxification Support

• Activated charcoal: 2 capsules, 2–3x daily (take 30 min before or 90 min after other treatments)
• Epsom salt baths: dissolve 2–4 cups in a warm bath and soak for 20 minutes
• Liposomal glutathione: 500–1,000 mg, 1–2x daily
• N-acetyl cysteine (NAC): If liposomal glutathione isn’t tolerated, try 1 capsule of NAC, 1–2x daily

A Note for People With MCAS

We’ve found that our clients with mast cell activation syndrome or MCAS (a condition in which histamine-releasing mast cells are hypersensitive) may have more extreme Herx reactions. 

A Herx reaction may also amplify mast cell activation, leading to MCAS flare-ups. 

Currently we’re working on finding the best support strategies for people with both MCAS and Herx reactions. The anti-inflammatory and detoxification support above may be helpful along with additional natural or over-the-counter antihistamines. 

Adjusting Dose or Protocol

If the above support tips don’t help, we’ll counsel clients to reduce the dose of antimicrobials in half until their reaction calms down—then slowly increase the dose every few days. 

If this still doesn’t resolve die-off symptoms or make them tolerable, we’ll often pause the antimicrobials completely until symptoms improve. Then, we’ll restart at ¼ or ½ the recommended dose and gradually increase it.

If you find navigating this on your own challenging, work with your trusted healthcare provider. They can work with you to pinpoint what isn’t working and adjust your plan. If you don’t have one or would like to try a different approach, our clinic is now accepting new patients, and we are well-versed in antimicrobial therapy. We’d love to help.

Shirk the Herx? No—Embrace It Instead

Herxheimer reactions are a normal—though sometimes uncomfortable—part of the healing process, especially when addressing chronic infections, gut dysbiosis, or vector-borne pathogens. In the functional health context, we don’t see Herx reactions as setbacks, but rather as a sign that your body is actively responding to treatment and clearing out harmful pathogens.

That said, these reactions can sometimes be confusing and difficult to manage on your own—particularly when symptoms are severe, prolonged, or unclear. If you’re unsure whether what you’re experiencing is microbial die-off, a food sensitivity, or something else, it’s a good idea to work with an expert who can help fine-tune your protocol and support your recovery.

Our clinicians have extensive experience guiding clients through Herxheimer reactions. If you need support, reach out to us at the Ruscio Institute for Functional Health. You can also explore the 8-step protocol in Healthy Gut, Healthy You— offering helpful strategies during this phase of your healing journey.

The Ruscio Institute has developed a range of high-quality formulations to help our clients and audience. If you’re interested in learning more about these products, please click here. Note that there are many other options available, and we encourage you to research which products may be right for you. The information on DrRuscio.com is for educational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment.