Paxlovid vs. Ivermectin: What the Science Says

Paxlovid has strong clinical trial evidence showing it reduces COVID-19 hospitalizations and deaths in high-risk patients, while ivermectin has consistently failed to demonstrate meaningful benefit against the disease in well-designed trials. The two drugs are not close competitors with mixed results; one earned regulatory authorization on the strength of a rigorous trial showing roughly an 89% reduction in hospitalization risk, while the other became a cultural flashpoint whose clinical promise evaporated as study quality improved. The story behind that divergence involves pharmacology, trial design, and a remarkable episode in the sociology of science.

How Each Drug Is Supposed to Work

Paxlovid is a two-drug combination. The active ingredient, nirmatrelvir, blocks the SARS-CoV-2 main protease, an enzyme the virus needs to chop up its own proteins and replicate inside human cells. Without a functioning protease, the virus produces defective copies of itself and the infection stalls. Nirmatrelvir was designed from scratch for this purpose. The second component, ritonavir, does not fight the virus directly. It slows the liver’s breakdown of nirmatrelvir so that blood levels stay high enough to work.¹

Ivermectin, by contrast, was developed decades ago as an anti-parasitic drug. It is highly effective against roundworms and certain other parasites, and its discoverers won a Nobel Prize for that contribution. In early 2020, a lab study showed that ivermectin could inhibit SARS-CoV-2 in cell cultures, which set off enormous public interest. The catch was immediately apparent to pharmacologists: the concentration needed to stop the virus in a dish was more than 35 times higher than what you can achieve in human blood with the approved oral dose.² Even modeling a dose ten times the approved amount, predicted lung tissue concentrations still fell far short of the level needed to inhibit the virus.³ In plainer terms, ivermectin kills the virus in a test tube at concentrations you cannot safely reach in a living person.

What the Major Trials Found for Paxlovid

The trial that led to Paxlovid’s emergency authorization, known as EPIC-HR, enrolled unvaccinated adults at high risk for severe COVID-19. Among patients treated within three days of symptom onset, fewer than 1% of those who received Paxlovid were hospitalized or died within 28 days, compared with about 7% in the placebo group. That translated to a relative risk reduction of roughly 89%. All 13 deaths during the trial occurred in the placebo group.⁴ Those are striking numbers, though the context matters: the participants were unvaccinated and had no prior infection, a population that barely exists anymore.

A later trial called EPIC-SR tested Paxlovid in vaccinated adults and those at standard risk, a group much closer to today’s typical COVID patient. The results were far less dramatic. Hospitalization or death occurred in about 0.8% of the Paxlovid group versus 1.6% in the placebo group, a difference that was not statistically significant. Time to symptom recovery was nearly identical between the two groups.⁵ This does not mean Paxlovid stopped working. It means the baseline risk dropped so much in vaccinated people that there was less room for the drug to show a measurable benefit.

Real-world data from large observational studies has generally supported a benefit in older and higher-risk populations. A large U.S. electronic health records study found that Paxlovid-treated patients had about a third the odds of hospitalization compared to untreated patients.⁶ A study of elderly patients during the Omicron wave found a roughly 75% reduction in the risk of progressing from moderate to severe disease.⁷ In Singapore, treatment of community-dwelling elderly adults was independently associated with lower odds of hospitalization across multiple Omicron subvariants.⁸ South Korean national data found Paxlovid reduced severe illness or death by about 46% in patients aged 60 and older, regardless of vaccination status.⁹

What the Major Trials Found for Ivermectin

The largest and most rigorous ivermectin trials tell a consistent story. The TOGETHER trial, a well-powered adaptive platform trial in Brazil, found no meaningful benefit from ivermectin. About 15% of ivermectin-treated patients had a primary outcome event (mainly hospitalization), compared with about 16% in the placebo group. That small numerical difference was well within the range of chance.¹⁰

The PRINCIPLE trial in the United Kingdom, another large platform trial, found that ivermectin shortened self-reported recovery time by about two days compared with usual care, but the probability of a clinically meaningful effect fell well below the trial’s pre-set threshold. COVID-related hospitalizations and deaths were essentially the same in both groups. The trial investigators concluded that ivermectin is unlikely to provide clinically meaningful improvement in recovery, hospital admissions, or longer-term outcomes, and that further trials of ivermectin for COVID in vaccinated community populations are unwarranted.¹¹

A systematic review and meta-analysis that attempted to sort out the conflicting earlier literature found a telling pattern: studies with a higher risk of bias were more likely to report positive effects for ivermectin.¹² In other words, the worse the study design, the better ivermectin looked. As trial quality improved, the apparent benefit shrank and eventually disappeared. Several early studies that reported large positive effects were later retracted due to data fabrication or serious methodological problems, which further muddied the waters during 2020 and 2021.

Paxlovid Rebound

One well-known downside of Paxlovid is symptom and viral rebound. Some patients feel better after their five-day course, test negative, and then a few days later develop symptoms again with a positive test. One study found that about 21% of Paxlovid-treated participants experienced virologic rebound, compared with under 2% of untreated patients. Those who rebounded shed live virus for an average of 14 days, compared with fewer than 5 days in those who did not rebound, raising the possibility of extended contagiousness.¹³

The mechanism behind rebound is still not fully understood. Possible explanations include the virus persisting at high levels in tissue reservoirs even after symptoms improve, insufficient drug exposure during the five-day course, or incomplete immune clearance after the drug is withdrawn. Resistance to the drug is another theoretical possibility, though evidence for that as a primary driver of rebound remains thin.¹⁴ Rebound episodes are generally mild and do not typically lead to hospitalization, but they are annoying and can extend the period during which you need to isolate.

Drug Interactions and Safety Profiles

Paxlovid’s biggest practical headache is drug interactions. The ritonavir component powerfully inhibits the liver enzyme CYP3A4, which is involved in breaking down roughly 60% of available medications.¹⁵ If you take a drug that relies on CYP3A4 for metabolism, adding Paxlovid can cause that drug’s blood levels to spike, sometimes dangerously. This is a particular concern for people taking certain heart medications, blood thinners, immunosuppressants, and some psychiatric drugs.¹⁶ For many patients, these interactions can be managed by temporarily pausing or adjusting the interacting medication, but that requires coordination with a prescriber who knows the patient’s full drug list. For some drugs, the interaction is dangerous enough that Paxlovid is simply contraindicated.

Ivermectin at approved anti-parasitic doses has a well-established safety record stretching back decades. At the standard therapeutic dosage range, it does not readily cross the blood-brain barrier and serious side effects are rare.¹⁷ The safety picture changed during the pandemic, however, because some people took doses far above the approved range or used veterinary formulations. Patients who took veterinary products ingested higher doses and had higher rates of altered mental status than those taking prescription tablets.¹⁸ Veterinary formulations also contain excipients and secondary active ingredients tested only in animals, with unknown long-term effects in humans.¹⁹ A comprehensive toxicology review noted that the pandemic led to a substantial increase in toxic exposures to ivermectin without demonstrated clinical benefit, with rare but severe cases of encephalopathy, seizures, coma, and death at supratherapeutic doses.²⁰

Paxlovid and Long COVID

One question that has gained traction is whether treating the acute infection with Paxlovid reduces the risk of developing long COVID. The evidence here is early but suggestive. A large observational study from the RECOVER consortium found that Paxlovid-treated patients had a modestly lower overall risk of long COVID, with a hazard ratio of 0.88, translating to about 3 fewer cases per 100 people treated.²¹ A separate analysis using the same N3C data platform found that the overall effect on long COVID incidence was not statistically significant, but Paxlovid had small protective effects against specific symptom clusters, particularly cognitive symptoms and fatigue.²² These are observational studies with all their inherent limitations, but the direction of the signal is at least encouraging for people worried about post-acute symptoms. No comparable evidence exists for ivermectin and long COVID prevention.

The Resistance Question for Paxlovid

Any antiviral drug that becomes widely used faces the possibility that the virus evolves resistance. For nirmatrelvir, researchers have already identified mutations in the SARS-CoV-2 main protease that reduce the drug’s effectiveness. Some of these resistant variants existed before Paxlovid was even introduced, and phylogenetic analysis shows they are capable of spreading between people.²³ One triple-mutation variant commonly seen among clinical isolates showed more than a 20-fold decrease in sensitivity to nirmatrelvir, though it also came with a roughly 6-fold reduction in the enzyme’s own catalytic efficiency.²⁴ That tradeoff, where resistance comes at a fitness cost to the virus, is a common pattern in antiviral resistance and may slow the spread of highly resistant strains. But it is not a guarantee. Resistance monitoring will remain important as long as Paxlovid stays in clinical use.

Why the Debate Got So Heated

The Paxlovid-versus-ivermectin conversation was never purely a scientific one. From early in the pandemic, treatment preferences tracked with political identity, media consumption, and institutional trust in ways that went well beyond what the evidence could explain. A study published in the Proceedings of the National Academy of Sciences found that polarization around COVID treatments was driven partly by partisan cable news preferences, but also by something deeper: when the same scientific evidence was presented with the treatment identified as ivermectin, partisans evaluated it differently than when the treatment was unnamed.²⁵ The label changed how people interpreted the data.

Research in JAMA Health Forum found that the use of non-evidence-based treatments like ivermectin was associated not just with political affiliation but with endorsement of vaccine-related misinformation, mistrust of health care institutions, and conspiratorial thinking. These factors predicted treatment choices independently of party identification, and the effects of institutional trust persisted even after controlling for political orientation.²⁶ The framing of ivermectin as “suppressed” or “cheap and effective” created a narrative that was more about trust and identity than pharmacology. Paxlovid, marketed by Pfizer at significant cost, became a symbol of the opposite worldview for people predisposed to distrust pharmaceutical companies. The irony is that skeptics of mainstream medicine ended up taking a drug with no evidence of benefit while rejecting one with strong evidence, partly because the second one came from the institution they mistrusted.

Access and Cost

Even when the science is clear, access is not equally distributed. Paxlovid’s price and supply chain created barriers that ivermectin, as a cheap generic, did not face. A deal between Pfizer and the Medicines Patent Pool enabled 95 low- and middle-income countries to access affordable generic versions, but that deal excluded many middle-income countries that account for a large share of global COVID diagnoses. Those excluded nations faced high prices. And in countries with limited diagnostic testing capacity, the drug’s requirement for a confirmed positive test and early treatment start further limited real-world uptake.²⁷ Meanwhile, ivermectin’s appeal in some parts of the world was partly practical: it was already available in local pharmacies at low cost, no prescription was needed in many settings, and it did not require a same-day PCR test. That accessibility made it attractive even after the clinical evidence came in negative, especially in regions where Paxlovid was simply unavailable.

Veterinary Formulations and Self-Dosing

One of the more alarming chapters in the ivermectin story involved people purchasing and consuming formulations designed for horses and cattle. These products contain concentrations calibrated for animals weighing hundreds of kilograms, and the paste or liquid delivery systems make precise human dosing extremely difficult. Beyond the active ingredient, veterinary formulations contain excipients and secondary active compounds like clorsulon that have never been tested for safety in humans.¹⁹ Poison control centers saw a surge in calls related to ivermectin toxicity during peak waves of interest, and patients who had taken veterinary products presented with more severe symptoms, particularly neurological effects, than those who had taken human-grade tablets.¹⁸ At therapeutic doses in humans, ivermectin is a safe drug. The pandemic problem was never ivermectin’s safety profile under normal use. It was the combination of no benefit against COVID and the serious risks people created for themselves by taking inappropriate doses of inappropriate formulations.

Where Paxlovid Benefits Are Clearest and Where They Fade

If you are trying to figure out whether Paxlovid is worth taking, the answer depends heavily on your risk profile. The drug’s benefit is most clearly demonstrated in people who are older, immunocompromised, or unvaccinated, groups where the baseline risk of severe disease is high enough that reducing it by even a moderate proportion translates to a meaningful absolute benefit. In the original trial of high-risk unvaccinated patients, you needed to treat about 15 people to prevent one hospitalization.⁴ In the Singapore real-world data of elderly patients, that number rose to about 150, reflecting the lower baseline risk in a more vaccinated population.⁸ For a young, vaccinated, otherwise healthy person, the absolute benefit is quite small, and the drug interactions and rebound risk may not be worth it. For an 80-year-old on immunosuppressive therapy, the calculus is entirely different.

Ivermectin, on the other hand, does not have a clearly demonstrated benefit in any identified subgroup of COVID patients. The TOGETHER trial investigators noted that a small treatment effect could not entirely be ruled out, but even the most charitable reading of the data offers nothing that would change clinical decision-making.²⁸ The PRINCIPLE trial’s conclusion that further trials of ivermectin in vaccinated community populations appear unwarranted effectively closed the book on this question for most of the infectious disease research community.¹¹

1
PubMed Central. The history, mechanism, and perspectives of nirmatrelvir (PF-07321332): an orally bioavailable main protease inhibitor used in combination with ritonavir to reduce COVID-19-related hospitalizations
2
PubMed Central. The Approved Dose of Ivermectin Alone is not the Ideal Dose for the Treatment of COVID-19
3
PubMed Central. Development of a Minimal Physiologically-Based Pharmacokinetic Model to Simulate Lung Exposure in Humans Following Oral Administration of Ivermectin for COVID-19 Drug Repurposing
4
PubMed Central. Oral Nirmatrelvir for High-Risk, Nonhospitalized Adults with Covid-19
5
PubMed Central. Nirmatrelvir for Vaccinated or Unvaccinated Adult Outpatients with Covid-19
6
PubMed Central. Effect of Nirmatrelvir/Ritonavir (Paxlovid) on Hospitalization among Adults with COVID-19: an EHR-based Target Trial Emulation from N3C
7
PubMed Central. Safety and Efficacy of Paxlovid Against Omicron Variants of Coronavirus Disease 2019 in Elderly Patients
8
PubMed Central. Real-world effectiveness of nirmatrelvir/ritonavir against COVID-19 hospitalisations and severe COVID-19 in community-dwelling elderly Singaporeans during Omicron BA.2, BA.4/5 and XBB transmission
9
Journal of Korean Medical Science. Effectiveness of Paxlovid, an Oral Antiviral Drug, Against the Omicron BA.5 Variant in Korea: Severe Progression and Death Between July and November 2022
10
PubMed. Effect of Early Treatment with Ivermectin among Patients with Covid-19
11
PubMed Central. Ivermectin for COVID-19 in adults in the community (PRINCIPLE): An open, randomised, controlled, adaptive platform trial of short- and longer-term outcomes
12
PubMed Central. Ivermectin under scrutiny: a systematic review and meta-analysis of efficacy and possible sources of controversies in COVID-19 patients
13
Annals of Internal Medicine. One in Five Patients Experience Rebound COVID After Taking Paxlovid, New Study Finds
14
PubMed Central. Editorial: Rebound COVID-19 and Cessation of Antiviral Treatment for SARS-CoV-2 with Paxlovid and Molnupiravir
15
PubMed Central. Interactions listed in the Paxlovid fact sheet, classified according to risks, pharmacological groups, and consequences
16
PubMed Central. Cardiovascular Drug Interactions with Nirmatrelvir/Ritonavir for COVID-19: Considerations for Daily Practice
17
PubMed Central. Identifying the Toxidrome of Ivermectin Toxicity
18
PubMed. Characteristics of ivermectin toxicity in patients taking veterinary and human formulations for the prevention and treatment of COVID-19
19
Die Pharmazie – An International Journal of Pharmaceutical Sciences. Quantification of ivermectin in veterinary products consumed off-label as a treatment for COVID-19
20
PubMed Central. Ivermectin Toxicity in Humans and Animals: Clinical Spectrum, Mechanisms, and Management
21
PubMed Central. Real-World Effectiveness of Nirmatrelvir in Protecting Long COVID for Outpatient Adult Patients – A Large-Scale Observational Cohort Study from the RECOVER Initiative
22
PubMed Central. Effect of Paxlovid treatment during acute COVID-19 on Long COVID onset: An EHR-based target trial emulation from the N3C and RECOVER consortia
23
PubMed Central. Transmissible SARS-CoV-2 variants with resistance to clinical protease inhibitors
24
PubMed Central. An Investigation of Nirmatrelvir (Paxlovid) Resistance in SARS-CoV-2 Mpro
25
PubMed Central. The political polarization of COVID-19 treatments among physicians and laypeople in the United States
26
JAMA Health Forum. Misinformation, Trust, and Use of Ivermectin and Hydroxychloroquine for COVID-19
27
PubMed Central. Barriers to Worldwide Access for Paxlovid, a New Treatment for COVID-19
28
Collaborative Health Education. Paxlovid vs. Ivermectin: What the Science Says