Paxlovid: what it treats, how to take it, side effects
Last updated September 3, 2026.
Paxlovid is a COVID-19 antiviral - two medicines, nirmatrelvir and ritonavir, packaged together. Nirmatrelvir stops the virus from spreading in the body; ritonavir boosts how much of it stays available. It is the pill that keeps high-risk COVID out of the hospital, and the clock starts the day symptoms do.
What does it treat?
Mild to moderate COVID-19 in adults - and in children 12 and older weighing at least 88 pounds - who are at risk of the illness becoming severe enough to cause hospitalization or death. It is treatment, not prevention, and the label is clear that it works when started early: as soon as possible after diagnosis and within 5 days of symptom onset.
How do you take it?
Three tablets, twice a day, for 5 days: two 150 mg nirmatrelvir tablets plus one 100 mg ritonavir tablet, all swallowed together, with or without food, at the same times each day. Do not split, chew, or crush them. Kidney disease changes the dose - your prescriber adjusts it. Finish all 5 days even if you feel better on day two; stopping early can leave the infection incompletely treated. Missed dose: if you are within 8 hours of the usual time, take it; if more than 8 hours, skip it and never double up.
Side effects to know
- Common: an altered or metallic taste, diarrhea, nausea or vomiting, headache, muscle aches, abdominal pain, and a general ill feeling.
- Serious - stop and call your doctor immediately: rash, redness, or itching; difficulty breathing or shortness of breath; swelling of the tongue, lips, or mouth; and the liver cluster - loss of appetite, yellowing of the skin or eyes, dark-colored urine, or pale-colored stools.
Who should not take it?
This is the interaction drug of the decade. Ritonavir changes how your body handles a long list of other medications - some combinations can cause life-threatening side effects, so your doctor and pharmacist need your complete medication list before the first dose, and nothing new starts during the 5 days without a check. Flag HIV, kidney disease, and liver disease. If you take a ritonavir- or cobicistat-containing medicine for HIV or hepatitis C, keep taking it as prescribed during the course. Paxlovid can decrease the effectiveness of hormonal contraceptives, so a backup method during treatment. If you become pregnant, call your doctor.
When is it an emergency?
Difficulty breathing or swelling of the tongue, lips, or mouth is a 911 call. Yellowing skin or eyes with dark urine means same-day care. For an overdose, call Poison Control at 1-800-222-1222. Pymander's escalation routing is built and tested specifically for this class of decision; see the safety architecture working paper.
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Common questions
Why does Paxlovid have to be started within 5 days?
That is the window the label studied: start as soon as possible after diagnosis and within 5 days of symptom onset. The drug works by stopping the virus from spreading in the body - early on, there is spread left to stop. By the second week, the illness is mostly your immune system's response, and an antiviral has little to add. Positive test plus risk factors means calling the doctor that day.
Why does Paxlovid interact with so many medications?
Ritonavir is the booster half of the pair - it slows the liver enzymes that clear drugs so nirmatrelvir lasts longer. The same slowing affects many other medicines, which is why MedlinePlus opens with a warning that these interactions can cause life-threatening side effects. The fix is simple and absolute: your doctor and pharmacist review everything you take before dose one, and nothing new starts mid-course without asking.
Why does everything taste like metal on Paxlovid?
That is the drug's signature - altered taste is on the common-effects list and it is the one patients mention most. It is annoying and harmless, and it resolves after the 5 days. Cold drinks and stronger-flavored food make it easier to live with.
Does Paxlovid affect birth control?
It can. MedlinePlus says nirmatrelvir and ritonavir may decrease the effectiveness of hormonal contraceptives - pills, patches, rings, implants, injections, and IUDs - and advises another form of birth control or abstinence during treatment. Have that conversation with your doctor before the course starts.
Can I stop isolating once I am on Paxlovid?
No. MedlinePlus says to continue to isolate as directed by your doctor and keep up masking, distancing, and hand washing. Paxlovid lowers your risk of severe disease; it does not make you non-contagious. And if you do not feel better - or feel worse - after 5 days, tell your healthcare provider.
What happens if I miss a dose of Paxlovid?
The 8-hour rule: within 8 hours of the usual time, take it as soon as you remember; more than 8 hours late, skip it and take the next dose on schedule - never double up. The course is only 10 doses, so each one matters. Phone alarms, morning and evening, are the way through.