The most common side effect of Paxlovid is a bitter or metallic taste in your mouth, reported by about 5.6% of people who take it. Diarrhea is the second most common, occurring in about 3% of users. Most people finish the five-day course without serious problems, but there are several other effects worth knowing about, from digestive issues to rare allergic reactions.
The Metallic Taste (“Paxlovid Mouth”)
The signature side effect has earned its own nickname. “Paxlovid mouth” is a persistent bitter, metallic, or sour taste that can make food and drinks taste wrong for the entire course of treatment. In the main clinical trial, 5.6% of people taking Paxlovid experienced it compared to just 0.3% on placebo. The taste typically starts within the first day or two of treatment and fades after you finish the course.
The exact cause isn’t fully understood. One theory is that the drug or its breakdown products get secreted into saliva, where they activate the same taste receptors that detect metal salts. Some people describe it as constantly having a penny in their mouth. It’s harmless but genuinely unpleasant. Sucking on hard candy, chewing gum, or eating strongly flavored foods can help mask it while you’re on treatment.
Digestive Side Effects
Diarrhea affected about 3% of people in the main clinical trial, compared to 2% on placebo, making it a relatively modest increase. After Paxlovid became widely available, additional gastrointestinal effects were reported, including nausea, vomiting, and abdominal pain. Specific rates for these weren’t tracked as precisely as in the trial, but they’re considered uncommon. The digestive symptoms are generally mild and resolve once you stop taking the medication.
Drug Interactions
This is where Paxlovid gets complicated. One of its two components, ritonavir, is a powerful enzyme blocker. It works by slowing down the liver enzyme that would otherwise break down the antiviral drug too quickly. The problem is that this same enzyme processes dozens of other medications, so ritonavir can cause other drugs to build up to dangerously high levels in your body.
The list of interactions is long. Certain cholesterol medications, heart rhythm drugs, sedatives, blood thinners, seizure medications, and even some herbal supplements like St. John’s wort can cause serious problems when combined with Paxlovid. This is why the prescriber will review your full medication list before writing a prescription. In some cases, you may need to temporarily pause another medication while taking Paxlovid. In others, Paxlovid simply isn’t safe to use.
If you take any prescription medications regularly, especially for heart conditions, organ transplants, or seizures, make sure your prescriber has a complete and current list before you start.
Allergic Reactions
Allergic reactions to Paxlovid are rare but can range from mild to severe. Reported symptoms include hives, itching, skin rashes, and facial swelling. More serious reactions have involved throat tightness, tongue swelling, difficulty breathing, and difficulty swallowing. Cases of anaphylaxis and severe skin reactions (Stevens-Johnson syndrome) have been reported with ritonavir, though these are extremely uncommon.
These reactions can happen even after a single dose. If you develop a rash, hives, swelling of your lips or tongue, or any trouble breathing after taking Paxlovid, stop taking it and seek medical attention.
Liver Effects
The ritonavir component has been associated with elevated liver enzymes, clinical hepatitis, and jaundice. People with pre-existing liver disease or hepatitis are at higher risk. Paxlovid is not recommended for anyone with severe liver impairment. If you have moderate liver issues, your prescriber should weigh the risks carefully before starting treatment.
Kidney Function and Dosing
Your kidney function affects how Paxlovid is dosed. People with moderate kidney impairment receive a reduced dose: one antiviral tablet instead of two, paired with the standard ritonavir tablet, twice daily for five days. If kidney function is severely reduced, Paxlovid is not recommended. Getting the dose wrong in someone with reduced kidney function can increase the concentration of the drug in the body and raise the risk of side effects, which is why prescribers check kidney function before writing a prescription.
COVID Rebound After Treatment
Some people test negative and feel better after finishing Paxlovid, only to have symptoms return or test positive again a few days later. This phenomenon, known as COVID rebound, generated significant attention. However, the data suggests it’s not unique to Paxlovid. A large observational study found rebound rates of about 6.6% in people who took Paxlovid, 4.8% in those who took a different antiviral, and 4.5% in people who received no treatment at all, with no statistically significant difference between the groups.
Some smaller studies reported higher rebound rates of 10% to 14% among treated patients, but these studies tended to include older people, those with more vaccine doses, and people on immune-suppressing medications, all of whom differ from untreated comparison groups in ways that could explain the difference. The initial clinical trial data showed similar viral rebound rates whether people took Paxlovid or a placebo. Rebound, when it happens, is typically mild and resolves on its own without additional treatment.
What Most People Experience
For the majority of people, Paxlovid’s side effects are limited to the unpleasant taste and possibly some mild digestive upset. These resolve within a day or two of finishing the course. The serious reactions, liver effects, and severe allergic responses are uncommon. The bigger practical concern for most people is whether their other medications are compatible with the drug, which is something to sort out with a prescriber before your first dose rather than after.