Treatments for influenza include a range of medications and therapies that are used in response to disease influenza. Treatments may either directly target the influenza virus itself; or instead they may just offer relief to symptoms of the disease, while the body's own immune system works to recover from infection.^[1]

The main classes of antiviral drugs used against influenza are neuraminidase inhibitors, such as zanamivir and oseltamivir, polymerase acidic endonuclease inhibitors such as baloxavir marboxil, or inhibitors of the viral M2 protein, such as amantadine and rimantadine. These drugs can reduce the severity of symptoms if taken soon after infection and can also be taken to decrease the risk of infection. However, virus strains have emerged that show drug resistance to some classes of drug.

The United States authority on disease prevention, the Centers for Disease Control and Prevention (CDC), recommends that people with influenza infections:

• Stay at home
• Get plenty of rest
• Drink a lot of liquids
• Do not smoke or drink alcohol
• Consider over-the-counter medications to relieve flu symptoms
• Consult a physician early on for best possible treatment
• Remain alert for emergency warning signs^[2]

Warning signs are symptoms that indicate that the disease is becoming serious and needs immediate medical attention. These include:^{[citation needed]}

• Difficulty breathing or shortness of breath
• Pain or pressure in the chest or abdomen
• Dizziness
• Confusion
• Severe or persistent vomiting

In children other warning signs include irritability, failing to wake up and interact, rapid breathing, and a blueish skin color. Another warning sign in children is if the flu symptoms appear to resolve, but then reappear with fever and a bad cough.^[2]

Antiviral drugs directly target the viruses responsible for influenza infections. Generally, anti-viral drugs work optimally when taken within a few days of the onset of symptoms.^[3] Certain drugs are used prophylactically, that is they are used in uninfected individuals to guard against infection.^{[medical citation needed]}

Four licensed influenza antiviral agents are available in the United States: zanamivir, oseltamivir phosphate, peramivir, and baloxavir marboxil.^[4] They are available through prescription only.^[4]

In Russia and China a drug called arbidol is also used as a treatment. Testing of the drug has predominantly occurred in these countries and, although no clinical trials have been published demonstrating this is an effective drug, some data suggest that this could be a useful treatment for influenza.^[5][6]

Influenza viruses can show resistance to anti-viral drugs. Like the development of bacterial antibiotic resistance, this can result from over-use of these drugs. For example, a study published in the June 2009 Issue of Nature Biotechnology emphasized the urgent need for augmentation of oseltamivir (Tamiflu) stockpiles with additional antiviral drugs including zanamivir (Relenza) based on an evaluation of the performance of these drugs in the scenario that the 2009 H1N1 'Swine Flu' neuraminidase (NA) were to acquire the tamiflu-resistance (His274Tyr) mutation which is currently widespread in seasonal H1N1 strains.^[17] Yet another example is in the case of the amantadines treatment may lead to the rapid production of resistant viruses, and over-use of these drugs has probably contributed to the spread of resistance.^[18] In particular, this high-level of resistance may be due to the easy availability of amantadines as part of over-the-counter cold remedies in countries such as China and Russia,^[19] and their use to prevent outbreaks of influenza in farmed poultry.^[20][21]

On the other hand, a few strains resistant to neuraminidase inhibitors have emerged and circulated in the absence of much use of the drugs involved, and the frequency with which drug resistant strains appears shows little correlation with the level of use of these drugs.^[22] However, laboratory studies have shown that it is possible for the use of sub-optimal doses of these drugs as a prophylactic measure might contribute to the development of drug resistance.^[22]

During the United States 2005–2006 influenza season, increasing incidence of drug resistance by strain H3N2 to amantadine and rimantadine led the CDC to recommend oseltamivir as a prophylactic drug, and the use of either oseltamivir or zanamivir as treatment.^[23][24]

Antiviral drugs are prescription-only medication in the United States. Readily available over-the-counter medications do not directly affect the disease, but they do provide relief from influenza symptoms, as illustrated in the table below.

Children and teenagers with flu symptoms (particularly fever) should avoid taking aspirin as taking aspirin in the presence of influenza infection (especially Influenzavirus B) can lead to Reye syndrome, a rare but potentially fatal disease of the brain.^[26]

Several generic prescription medications might prove useful to treat a potential H5N1 avian flu outbreak, including statins, fibrates, and chloroquine.^[27][28][29]

Malnutrition can reduce the ability of the body to resist infections and is a common cause of immunodeficiency in the developing world.^[30] For instance, in a study in Ecuador, micronutrient deficiencies were found to be common in the elderly, especially for vitamin C, vitamin D, vitamin B-6, vitamin B-12, folic acid, and zinc, and these are thought to weaken the immune system or cause anemia and thus place people at greater risk of respiratory infections such as influenza.^[31] Seasonal variation in sunlight exposure, which is required for vitamin D synthesis within the body, has been proposed as one of the factors accounting for the seasonality of influenza.^[32] A meta-analysis of 13 studies indicated some support for adjunctive vitamin D therapy for influenza, but called for more rigorous clinical trials to settle the issue conclusively.^[33]

A recent review discussing herbal and alternative medicines in influenza treatment details evidence suggesting that N-acetylcysteine, elderberry, or a combination of Eleutherococcus senticosus and Andrographis paniculata may help to shorten the course of influenza infection. The article cites more limited evidence including animal or in vitro studies to suggest possible benefit from vitamin C, DHEA, high lactoferrin whey protein, Echinacea spp., Panax quinquefolium, Larix occidentalis arabinogalactans, elenolic acid (a constituent of olive leaf extract), Astragalus membranaceus, and Isatis tinctoria or Isatis indigotica. ^[34] Another review assessed the quality of evidence for alternative influenza treatments, it concluded that there was "no compelling evidence" that any of these treatments were effective and that the available data on these products is particularly weak, with trials in this area suffering from many shortcomings, such as being small and poorly-designed and not testing for adverse effects.^[35]