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How long does it take for Xofluza to work?

Medically reviewed by Last updated on Nov 25, 2020.

Official Answer


In general, it takes about 1 to 2 days in adults for their flu symptoms to downgrade to the mild absent level after taking Xofluza (baloxavir marboxil).

Xofluza can reduce the amount of time a person is sick by one day or more.

Xofluza is an antiviral medicine used to:

  • treat the flu (influenza) in people 12 years of age and older who have had flu symptoms for no more than 48 hours.
  • prevent the flu in people 12 years of age and older following contact with a person who has the flu (post-exposure prophylaxis).

In clinical studies with Xofluza, investigators looked at alleviation of acute uncomplicated flu symptoms such as:

  • cough
  • sore throat
  • nasal congestion
  • headache
  • feverishness
  • muscle aches
  • fatigue.

"Time to alleviation" of these 7 symptoms was defined as the time it took to be rated by the patient as none or mild for at least 21.5 hours.

  • In adults, time to alleviation of symptoms with a single, oral dose of Xofluza 40 mg occurred in a median of 50 hours (with a range 45 to 64 hours) compared to 78 hours (range 68 to 89 hours) in those receiving a placebo (inactive pill).
  • In children 12 and older, a single dose of Xofluza (40 or 80 mg, based on weight) resulted in time to alleviation of symptoms in 54 hours (range 50 to 59 hours) compared to 80 hours (range 73 to 87 hours) in the placebo group.
  • In both studies, Xofluza treatment at these doses resulted in a statistically significant shorter time to alleviation of symptoms compared with placebo.
  • When Xolfuza was compared to Tamiflu (oseltamivir), another FDA-approved flu antiviral treatment taken twice a day for 5 days, there was no difference in the time to alleviation of symptoms (a median of 54 hours for each group).
  • Xofluza must be taken within the first two days (48 hours) after flu symptoms begin.
  • The US Centers for Disease Control (CDC) strongly recommends that everyone over the age of six months get a flu vaccine to help prevent the flu as soon as it is available each fall.

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