Canadian doctors prescribe one dose of this antibiotic to prevent Lyme disease. Here’s why that’s a bad idea

If you go to a family doctor’s office with a tick bite you might find yourself at the centre of a growing controversy about how to prevent Lyme disease. 

For more than two decades, there’s been one recommended treatment in Canada for patients who: 

• Discover and remove a blacklegged tick that’s been feeding for up to 72 hours,
• Live in an area where Lyme disease is endemic,
• Haven’t yet had any visible Lyme symptoms, such as the erythema migrans (EM) rash.

In these cases, doctors are advised to prescribe a single 200-milligram dose of an antibiotic called doxycycline to prevent the patient from developing Lyme disease. .

The protocol is backed by Health Canada and public health authorities in Nova Scotia – where pharmacists can prescribe single-dose doxycycline for tick bites – as well as in Ontario (PDF), Manitoba and other jurisdictions where Lyme disease is widespread. But critics say it’s deeply flawed. 

“We hear reports of patients showing up at doctors’ offices in endemic regions with the EM rash already present who then receive a single dose of doxycycline,” says Dr. Janet Sperling, president of the Canadian Lyme Disease Foundation (CanLyme).

Doctors often prescribe the one dose of doxycycline without scheduling a subsequent appointment to monitor patients for symptoms.

“This is a serious misinterpretation of the efficacy of doxycycline in preventing the appearance of the EM rash,” Sperling continues. 

“Furthermore, with no follow-up of this public health experiment, we have no idea how many Canadians go on to develop symptoms of Lyme or other tick-borne diseases.”

That lack of data is a more urgent problem than ever. Lyme disease is already Canada’s most common vector-borne illness. Even so, at least one estimate puts the number of cases at more than 13 times this country’s reported total since 2009. 

Meantime, climate change is enabling a full-scale invasion of the ticks that carry the Lyme pathogen. In endemic areas, ticks can latch on to you, your children or your pets almost anywhere — rural areas, forests, city parks, school playgrounds, even your backyard. So doctors in several regions of Canada are likely to see many more tick bites than in the past.

Why it’s recommended 

Canada isn’t the only country where it’s the recommended treatment. Health authorities in the United States also advise doctors to prescribe the one dose of doxycycline in these circumstances.

The rationale for the protocol rests on a small study titled “Prophylaxis with Single-Dose Doxycycline for the Prevention of Lyme Disease after an Ixodes scapularis Tick Bite”, published in the New England Journal of Medicine in 2001.

In areas of New York State where Lyme disease is extremely widespread, the researchers “conducted a randomized, double-blind, placebo-controlled trial of treatment with a single 200-mg dose of doxycycline in 482 subjects who had removed attached blacklegged ticks from their bodies within the previous 72 hours,” the authors write.

“At base line, three weeks, and six weeks, subjects were interviewed and examined, and serum antibody tests were performed, along with blood cultures for Borrelia burgdorferi,” the bacterium that causes Lyme disease, the article states.

“Erythema migrans developed at the site of the tick bite in a significantly smaller proportion of the subjects in the doxycycline group than of those in the placebo group.”

But Sperling says the study provides a flimsy foundation for the protocol, not least because it mostly focuses on the EM rash and not on other evidence of systemic disease. 

“In the decades since the 2001 publication… there has been nothing published to support this significant treatment decision,” Sperling says. 

“Important policy decisions are being based on a very small sample size,” she adds. Sperling also points to a cautionary statement in the article itself.

“The efficacy rate found in our study should be interpreted cautiously, however, because of the relatively small number of subjects in whom Lyme disease developed,” the authors write. 

A false sense of safety

The standard testing method used in Canada detects antibodies to Borrelia burgdorferi, not the pathogen itself, and those antibodies don’t show up  for several weeks. Sperling warns the use of doxycycline so soon after a tick bite can often kill enough of the bacteria to prevent the EM rash from appearing, dampen the immune response and render it undetectable, while not entirely eradicating the infection. 

She and other critics say Lyme disease often continues to develop undetected long after the arbitrary six-week testing limit set by the researchers.They also point out blacklegged ticks carry other pathogens that doxycycline isn’t effective against. 

“The study didn’t follow people long enough to detect cases of Lyme disease that develop without a rash, or cases involving co-infections like Babesia,” says Dr. Daniel Cameron, a widely recognized expert in the diagnosis and treatment of Lyme disease and a former president of the International Lyme And Associated Diseases Society (ILADS).

In a article for lymedisease.org, published in July 2025 and titled Why single-dose doxycycline after a tick bite is bad medicine, Cameron says many doctors fail to warn patients about the limitations of the single-dose doxycycline protocol.

“The idea of ‘just one pill’ sounds great—but it can create a false sense of safety. When patients aren’t told the full story, they lose the chance to make informed decisions,” he writes.

“And when symptoms are dismissed, the consequences can last for months or even years.” 

Cameron says health-care professionals should follow these guidelines when prescribing the single-dose protocol:

• Be honest about what the single-dose approach can and can’t do,
• Offer follow-up when patients remain unwell,
• Consider co-infections and other risks—not just following a checklist.

What’s the alternative?

CanLyme “does not support the use of a single dose of doxycycline for post-tick bite treatment without longer term follow up of patients with known tick bites,” Sperling says.

For its part, ILADS recommends a 20-day course of doxycycline for patients with a known bite from a blacklegged tick, instead of just the one 200-milligram dose. 

“All patients should be reassessed at the end of their initial therapy and, when necessary, antibiotic therapy should be extended,” the society says on its website.

But Sperling isn’t sold on that approach either. She says the ILADS protocol is “far too rigid,” because it doesn’t specify the severity of the tick bite or whether it happened in an endemic region.  

“I can’t justify 20 days of doxycycline unless there is a reasonable likelihood of exposure. A tick that has just barely attached has a much lower likelihood of transmission than a tick that is well fed,” Sperling says.

“There are risks to the use of antibiotics that don’t seem to be appropriately considered with a blanket statement like ’20 days.’”

But if a blacklegged tick has been removed in a known endemic area, a 20-day course of doxycycline is “a good start,” Sperling says.

“Even with 20 days, there should be follow up. It’s hard to know if the tick transmitted babesiosis … or if the particular patient requires a second round of antibiotics.” 

Above all, Sperling says, doctors should be trained to use their professional judgment when treating Lyme disease. And they should present their patients with options rather than using a cookie-cutter approach to their care.

“People with cancer are offered choices so people with Lyme disease should be offered choices, too.”

References

Cameron DJ, Maloney EL. 2021. Insufficient evidence to advise a single dose of doxycycline to prevent lyme disease from an ixodes tick bite. Journal of Infection. 82(1):159–198. doi:10.1016/j.jinf.2020.07.014.

Cameron DJ, Maloney EL. 2021. Insufficient evidence to advise a single dose of doxycycline to prevent lyme disease from an ixodes tick bite. Journal of Infection. 82(1):159–198. doi:10.1016/j.jinf.2020.07.014.

Maloney EL. 2021. Evidence-based, patient-centered treatment of erythema migrans in the United States. Antibiotics. 10(7):754. doi:10.3390/antibiotics10070754.

Maloney EL. 2016 Oct. Controversies in persistent (chronic) lyme disease. Journal of Infusion Nursing.:1. doi:10.1097/nan.0000000000000195.

Lloyd V, Hawkins R. 2018. Under-detection of lyme disease in Canada. Healthcare. 6(4):125. doi:10.3390/healthcare6040125.

Maloney EL, M.D. 2009. The need for clinical judgment in the diagnosis and treatment of lyme disease. In: Journal of American Physicians and Surgeons. Vol. 14. p. 82. [accessed 2026 Nov 4]. https://www.jpands.org/vol14no3/maloney.pdf.

Nadelman RB, Nowakowski J, Fish D, Falco RC, Freeman K, McKenna D, Welch P, Marcus R, Agüero-Rosenfeld ME, Dennis DT, et al. 2001. Prophylaxis with single-dose doxycycline for the prevention of lyme disease after anIxodes scapularisTick bite. New England Journal of Medicine. 345(2):79–84. doi:10.1056/nejm200107123450201.

Books

Chronic, The Hidden Cause of the Autoimmune Pandemic…Stephen Phillips, MD and Dana Parish 2020 HMH https://aclibrary.bibliocommons.com/v2/record/S163C2359445 

Crypto Infections, Dr. Christian Perronne, Hammersmith Books 2021 https://hammersmithbooks.co.uk/product/crypto-infections/ 

Conquering Lyme Disease, Science Bridges the Great Divide, Brian A. Fallon, MD & Jennifer Sotsky, MD, Columbia Press 2018 https://cup.columbia.edu/book/conquering-lyme-disease/9780231183857/ 

Lyme, the First Epidemic of Climate Change, Mary Beth Pfeiffer, Island Press 2018 

Cure Unknown, Inside the Lyme Epidemic, Pamela Weintraub, St. Martin’s Griffin 2013 https://discover.bklynlibrary.org/item?b=11746584 

Web articles, letters, and press items

Researchers say visible signs of Lyme disease are easily missed, News, Lymedisease.org 2013-04-23: https://www.lymedisease.org/umdnj-pr-2/

Single dose prophylactic treatment of a tick bite only prevents a Lyme rash, Cameron DL, Lyme Science Blog: https://danielcameronmd.com/importance-second-opinion-prophylactic-treatment-tick-bite/

Why single-dose doxycycline after a tick bite is bad medicine, Dr. Daniel Cameron, Lymedisease.org 2025 Jul 16: https://www.lymedisease.org/one-dose-doxy-bad-medicine/

Will 2 Pills Prevent Lyme Disease? Ahern H, Lyme Action Network, YouTube 2015-03-24: https://www.youtube.com/watch?v=QmSJnIszv28 

The Potential Problem with Single Dose Doxycycline for Tick Bites, VTLyme.org: https://vtlyme.org/2017/04/24/problem-single-dose-doxycycline-tick-bites/

Post tick-bite antibiotic prophylaxis to prevent Lyme disease, INESSS Report, Guides and Standards, May 2019: Post-Tick Bite Antibiotic Prophylaxis to Prevent Lyme Disease

Focusing on the Bull’s Eye You May Miss the Mark, Stonehouse A, et al., Thomas Jefferson University 2007-10-18: https://jdc.jefferson.edu/cgi/viewcontent.cgi?referer=https://www.google.com/&httpsredir=1&article=1007&context=fmfp

There’s no evidence quick dose of antibiotics will stave off Lyme, Counterpoint, Bailey J, The Chronicle Herald 2019-05-07: https://www.thechronicleherald.ca/opinion/counterpoint-theres-no-evidence-quick-dose-of-antibiotics-will-stave-off-lyme-309057/

Why does the CDC endorse single-dose doxy to prevent Lyme? Marcum L, Lyme Sci 2020-02-04: https://www.lymedisease.org/lyme-sci-single-dose-doxy/

The problem of Lyme disease misdiagnosis: MyLymeData Viz.Blog: https://www.lymedisease.org/mylymedata-lyme-disease-misdiagnosis/

How many of those with a rash get diagnosed with Lyme disease? Lymedisease.org 2014: https://www.lymedisease.org/lymepolicywonk-how-many-of-those-with-lyme-disease-have-the-rash-estimates-range-from-27-80-2/

Ticks can transmit infection the first day, Lymedisease.org, Mervine P 2013-08-28: https://www.lymedisease.org/hard-science-on-lyme-ticks-can-transmit-infection-the-first-day/

Study finds nymphal ticks can transmit Lyme within 12 hours, Insitut Pasteur, News, Lymedisease.org: https://www.lymedisease.org/tick-lyme-transmission-time/

Tick Bite Never Zero Risk, Mervine P, Lymedisease.org 2013-07-05: https://www.lymedisease.org/hard-science-on-lyme-tick-bite-never-zero-risk/