Unproven treatments for symptoms sometimes described as “chronic Lyme disease” can be dangerous and even deadly, according to a recent report from the Centers for Disease Control and Prevention (CDC).

The paper, published in Morbidity and Mortality Weekly, documents several cases from recent years in which long courses of IV antibiotics and other supposed remedies led to septic shock and serious bacterial infections. What’s more, the authors say, there’s no evidence these treatments actually help the patients who seek them out.

Chronic Lyme disease is not a medical diagnosis, and the CDC recommends against using the term at all. Still, some doctors use it to describe situations in which a confirmed case of Lyme disease is treated, but the patient still has lingering symptoms. This condition, which is estimated to occur in 10% to 20% of Lyme disease cases, is technically called post-treatment Lyme disease syndrome, or PTLDS.

Some doctors also use the term chronic Lyme disease to diagnose patients who have otherwise unexplained symptoms (including joint and muscle aches, fatigue, and neurological problems) but no actual evidence they were ever infected with Lyme in the first place.

When Lyme disease is caught early, within weeks of the first symptoms after a tick bite, most people recovery completely after a short course of oral antibiotics. For cases that have gone untreated for longer, a four-week course of IV antibiotics might be necessary.

If a person’s symptoms still don’t go away after that, though, that’s where confusion often sets in. Research on PTLDS is ongoing, and the cause of these symptoms is still unknown. Experts believe that some of these symptoms may be caused by residual damage to tissues and the immune system, and some may not be related to Lyme disease at all.

But one thing Lyme researchers know for sure is that longer courses of antibiotics do not lead to meaningful improvements; at least five randomized, placebo-controlled studies have shown this much. Nevertheless, some doctors still prescribe them for months or even years, says report co-author Christina Nelson, MD, medical epidemiologist for the CDC.

Other doctors or alternative-medicine practitioners recommend other unproven remedies—like IV infusions of peroxide, immunoglobulin therapy, hyperbaric oxygen therapy, electromagnetic frequency treatments, garlic supplements, colloidal silver, and stem cell transplants.

“We’ve known about cases like these for quite some time, but anecdotally, we did seem to be hearing about them more frequently,” says Dr. Nelson. A 2015 study noted a 50% increase in long-course antibiotic therapies prescribed for Lyme disease between 2004 to 2006 and 2010 to 2012.

Doctors who provide these treatments "don’t typically follow the most commonly recommended treatments and the evidence-based guidelines,” she says, and they may diagnose Lyme disease even if blood tests are negative. “Most general practitioners and infectious disease physicians would not provide this type of care.”

Besides being unproven, these treatments can be dangerous, says Dr. Nelson. In the paper, she and her co-authors describe a woman in her 30s who received a chronic Lyme diagnosis and, when oral antibiotics didn’t help her symptoms, was given three weeks of IV antibiotics.

She became sick and eventually died from septic shock. In another case of antibiotic-related septic shock, an adolescent girl survived but required several weeks of treatment in a hospital intensive-care unit.

Antibiotics work well for certain infections, but the use of long-term IV medicines—which require an “in-dwelling catheter” (often called a PICC line) to be inserted in the skin—can actually expose people to other dangerous bugs. “Other bacteria from the skin or from the hospital or wherever can enter through that IV line or attach to that IV line, and the drugs may not be effective against them.” says Dr. Nelson.

In another case described in the paper, a woman in her 40s tested positive for Lyme disease but didn’t feel better after four weeks of oral antibiotics. She received various IV antibiotic treatments over the next year and eventually developed back pain—which a scan revealed to be a serious bone infection.

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Another big concern with diagnosis of chronic Lyme disease is that the actual cause of a person’s symptoms could go ignored or untreated. This was the case for a 50-something woman diagnosed with amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig's disease. When she sought a second opinion, she was told she had chronic Lyme disease along with other tick-borne illnesses, babesiosis and Rocky Mountain Spotted Fever.

The woman was treated with herbs, homeopathic remedies, and antibiotic, antifungal, and antiviral drugs, and eventually developed an intestinal infection that caused severe cramps and diarrhea for more than two years. “She was on this cocktail of medications for months and months, and it set her up for the bad bacteria in her gut to take over and overpower the good bacteria,” says Dr. Nelson.

Dr. Nelson says the woman, who eventually died from complications of ALS, was simply trying to make sure she had pursued every possible treatment option for her symptoms. “She had gotten this devastating diagnosis, and understandably it can be hard to accept,” she says. “She wanted to make sure she was doing everything she could, and unfortunately this was a very tragic case.”

These are just a few of the cases reported to the CDC in recent years, says Dr. Nelson, but they bring to light the very real risks associated with these types of unproven treatments.