Influenza
Supplements studied for influenza.
Overview
Five supplements are indexed for influenza (9 studies), all at WA 40 with low ratings. Vitamin D (4 studies) has insufficient evidence in this dataset. Brewer's Yeast as the EpiCor product (2 studies) may modestly lower cold or influenza symptom incidence by about 10–20% over roughly three months in adults, including after influenza vaccination, without clearly reducing severity once symptoms start.
Aloe, Eleuthero, and Theanine each have single trials, often in combination products with other herbs, and standalone effects remain uncertain. Overall influenza supplement evidence is limited. See the evidence reviews below.
Effect graph
Relevant supplements
Relevant supplements sorted by DEX Score.
| Elderberry | ★★★★★ | Medium |
| Panax Ginseng | ★★★★★ | Medium |
| N-Acetyl Cysteine (NAC) | ★★★★★ | Medium |
| Green Tea | ★★★★★ | Low |
| Vitamin D | ★★★★★ | Low |
| Theanine | ★★★★★ | Low |
| Garlic | ★★★★★ | Low |
| Eleuthero | ★★★★★ | Low |
| Brewer's Yeast | ★★★★★ | Low |
| Aloe | ★★★★★ | Very Low / None |
Studies
Find individual evidence reviews for supplements sorted by DEX Score.
10 supplements for , and rated at least stars. All purchase bands. No minimum star filter.
ElderberryView supplement →
Consider purchase·★★★★★
How we scored this▸
- Taking elderberry syrup or lozenges soon after flu symptoms start may help reduce symptoms and make people feel better about 4 days earlier.
- But in a larger study including children and people with health problems, elderberry did not help shorten the illness.
- The effectiveness of elderberry varies based on who is treated and how benefits are measured.
- Combining elderberry with echinacea also has been tested but it is unclear if this works better than using either alone.
Browse 5 studies
RCTElderberry Extract Outpatient Influenza Treatment for Emergency Room Patients Ages 5 and Above: a Randomized, Double-Blind, Placebo-Controlled Trial2020n=44
In 87 ER patients with influenza over 5 days, elderberry extract did not significantly reduce time to symptom resolution (4.9 vs 5.3 days) or complete recovery (8.7 vs 8.6 days) versus placebo.
- Effect
- No Benefit
- Duration
- 5 days
- Dose
- 15 ml/day
- Population
- Influenza patients
- Participants
- 44
- Avg age
- ~25
RCTEffect of an Echinacea-Based Hot Drink Versus Oseltamivir in Influenza Treatment: A Randomized, Double-Blind, Double-Dummy, Multicenter, Noninferiority Clinical Trial2015n=473
In 473 influenza patients over 10 days, Echinaforce Hotdrink was noninferior to oseltamivir for clinical recovery (90.1% vs 84.8% by day 10) with fewer complications (2.5% vs 6.5%) and adverse events.
- Duration
- 10 days
- Population
- Influenza patients
- Participants
- 473
- Ages
- 12–70
Pilot Clinical Study on a Proprietary Elderberry Extract : Efficacy in Addressing Influenza Symptoms2009
A 2009 pilot clinical study of a proprietary elderberry extract for influenza symptoms; outcome details were not available in the indexed abstract.
RCTRandomized study of the efficacy and safety of oral elderberry extract in the treatment of influenza A and B virus infections2004n=60
In 60 influenza patients (18–54 years) over 5 days, elderberry syrup (15 mL four times daily) relieved symptoms ~4 days earlier and reduced rescue medication use versus placebo.
- Effect
- Benefit
- Duration
- 5 days
- Dose
- 15 mL 4 times/day
- Population
- Adults with influenza
- Participants
- 60
- Ages
- 18–54
RCTInhibition of several strains of influenza virus in vitro and reduction of symptoms by an elderberry extract (Sambucus nigra L.) during an outbreak of influenza B Panama1995
During an influenza B outbreak, Sambucol-treated patients showed improvement in 93.3% within 2 days versus 91.7% within 6 days with placebo (p < 0.001), with near-complete cure in 2–3 days versus ≥6 days.
- Effect
- Benefit
- Duration
- 6 days
- Population
- Adults
N-Acetyl Cysteine (NAC)View supplement →
Reconsider purchase·★★★★★
How we scored this▸
- Taking N-acetylcysteine 600 mg twice daily for 6 months may not stop you from getting the flu, but it can reduce the chance of developing flu symptoms by about two-thirds.
Browse 1 study
RCTAttenuation of influenza-like symptomatology and improvement of cell-mediated immunity with long-term N-acetylcysteine treatment1997n=262
A 6-month RCT of 262 elderly adults found NAC (600 mg) attenuated influenza-like symptoms and improved cell-mediated immunity versus placebo.
- Effect
- Benefit
- Duration
- 6 months
- Dose
- 600 mg
- Population
- Older adults
- Participants
- 262
Panax GinsengView supplement →
Reconsider purchase·★★★★★
How we scored this▸
- Taking Panax ginseng might lower the chance of catching the flu or cold.
- In studies, people who took it before and after flu shots or took higher doses over several weeks had fewer infections than those who didn’t.
- However, if they did get sick, Panax ginseng did not help make symptoms shorter or milder.
Browse 2 studies
RCTPreventive effect of Korean red ginseng for acute respiratory illness: a randomized and double-blind clinical trial2012n=100
In 100 healthy volunteers, Korean red ginseng 3 g/day for 12 weeks cut acute respiratory illness incidence (24.5% vs 44.9%, p=0.034) versus placebo.
- Effect
- Benefit
- Duration
- 12 weeks
- Dose
- 3 g/day
- Population
- Healthy adults
- Participants
- 100
- Ages
- 30–70
RCTEfficacy and safety of the standardised Ginseng extract G115 for potentiating vaccination against the influenza syndrome and protection against the common cold [corrected]1996n=227
In 227 adults, ginseng G115 100 mg/day for 12 weeks with flu vaccination cut cold/flu cases (15 vs 42, p<0.001) and raised antibody titres and NK cell activity versus placebo.
- Effect
- Benefit
- Duration
- 12 weeks
- Dose
- 100 mg/day
- Population
- Adults
- Participants
- 227
Green TeaView supplement →
Reconsider purchase·★★★★★
How we scored this▸
- It’s still unclear whether drinking or gargling green tea can reliably prevent the flu.
- Some studies suggest that green tea extracts, either swallowed as capsules or used as a mouth rinse, may lower the chance of getting the flu by about 30–50%.
- People who drink at least five cups of green tea a week may also have a lower risk, especially if they haven’t had a flu shot.
- However, other studies have shown no benefit.
- Green tea combined with the amino acid theanine has also been studied.
- In some small trials, people taking this combination daily had fewer flu and cold symptoms, or shorter illness duration, compared with those who took a placebo.
- More research is needed to know for sure how effective green tea and theanine are, and which form (drink, gargle, or capsule) works best.
Browse 5 studies·1 meta-analysis
MetaAnti-Influenza with Green Tea Catechins: A Systematic Review and Meta-Analysis2021n=5,048
A meta-analysis of eight studies (5,048 participants) found green tea catechins reduced influenza risk versus control (RR 0.67 in five RCTs and 0.52 in three cohort studies).
- Effect
- Benefit
- Participants
- 5,048
ObservationalGreen tea consumption and influenza infection among Japanese employees2020
In a case-control study of 4,302 Japanese workers (179 influenza cases), drinking green tea ≥5 cups/week was associated with lower influenza odds (OR 0.61) versus <1 cup/week.
- Effect
- Benefit
RCTEffects of green tea gargling on the prevention of influenza infection in high school students: a randomized controlled study2014n=757
In 757 Japanese high school students gargling green tea or water three times daily for 90 days, green tea did not significantly reduce laboratory-confirmed influenza versus water (4.9% vs 6.9%).
- Effect
- No Benefit
- Duration
- 90 days
- Population
- Children/adolescents
- Participants
- 757
- Ages
- 15–17
RCTEffects of green tea catechins and theanine on preventing influenza infection among healthcare workers: a randomized controlled trial2011n=197
In 197 healthcare workers over 5 months, green tea catechins (378 mg/day) plus theanine (210 mg/day) lowered clinically defined influenza versus placebo (4.1% vs 13.1%; adjusted OR 0.25).
- Effect
- Benefit
- Duration
- 5 months
- Dose
- 378 mg/day
- Population
- Older adults
- Participants
- 197
- Ages
- 20+
RCTSpecific formulation of Camellia sinensis prevents cold and flu symptoms and enhances gamma,delta T cell function: a randomized, double-blind, placebo-controlled study2007
In a 3-month double-blind RCT, a Camellia sinensis (green tea) capsule formulation reduced cold and flu symptom incidence and enhanced gamma-delta T-cell function versus placebo.
- Effect
- Benefit
- Duration
- 3 months
- Population
- Healthy adults
- Ages
- 18–70
Vitamin DView supplement →
Reconsider purchase·★★★★★
How we scored this▸
- Evidence is insufficient for this condition.
Browse 4 studies
RCTPreventive Effects of Vitamin D on Seasonal Influenza A in Infants: A Multicenter, Randomized, Open, Controlled Clinical Trial2018n=400
In a multicenter RCT of 400 infants, high-dose 1,200 IU/day vitamin D reduced influenza A episodes (43 vs 78 cases) and shortened fever, cough, and wheezing duration versus 400 IU/day.
- Effect
- Benefit
- Duration
- 4 months
- Dose
- 1200 IU/day
- Population
- Infants
- Participants
- 400
RCTEffects of vitamin D supplements on influenza A illness during the 2009 H1N1 pandemic: a randomized controlled trial2014n=247
In a 2-month RCT of 247 Japanese students during the 2009 H1N1 pandemic, 2,000 IU/day vitamin D did not lower overall influenza A incidence but reduced first-month cases (1.4% vs 8.1%).
- Effect
- No Benefit
- Duration
- 2 months
- Dose
- 2000 IU/day
- Participants
- 247
RCTVitamin D supplementation did not prevent influenza-like illness as diagnosed retrospectively by questionnaires in subjects participating in randomized clinical trials2011n=69
In 569 participants across 10 vitamin D trials, supplementation did not reduce influenza-like illness incidence; illness duration was longer in the vitamin D group among those reporting symptoms.
- Effect
- No Benefit
- Dose
- 6800 IU/day
- Participants
- 69
RCTRandomized trial of vitamin D supplementation to prevent seasonal influenza A in schoolchildren2010n=12
In a winter RCT of 334 schoolchildren, 1,200 IU/day vitamin D3 reduced influenza A incidence (10.8% vs 18.6%; RR 0.58) and asthma attacks in children with asthma (RR 0.17).
- Effect
- Benefit
- Dose
- 200 IU/day
- Population
- Children/adolescents
- Participants
- 12
- Ages
- schoolchildren
Brewer's YeastView supplement →
Reconsider purchase·★★★★★
How we scored this▸
- Taking 500 mg of the yeast-based supplement EpiCor daily for about 3 months may lower the chances of getting cold or flu symptoms by about 10-20% in adults who have not had a flu shot.
- For people who recently got a flu vaccine, EpiCor may reduce the risk of cold or flu symptoms by about 11% and help reduce symptom duration by one day.
- It doesn’t seem to make symptoms less severe once they start.
- EpiCor helps boost the immune system and is safe to take, but more research is needed to be sure how well it works for different people.
Browse 2 studies
RCTImmunogenic yeast-based fermentate for cold/flu-like symptoms in nonvaccinated individuals2010n=116
In 116 nonvaccinated adults over 12 weeks, 500 mg/day EpiCor yeast fermentate significantly reduced cold and flu-like illness incidence (p=0.01) versus placebo, with a favorable safety profile.
- Effect
- Benefit
- Duration
- 12 weeks
- Dose
- 500 mg/day
- Population
- Adults
- Participants
- 116
- Ages
- 18–76
RCTEffects of a modified yeast supplement on cold/flu symptoms2008n=116
In 116 healthy adults over 12 weeks (many recently vaccinated for influenza), 500 mg/day EpiCor significantly reduced cold/flu symptom frequency and duration compared with placebo.
- Effect
- Benefit
- Duration
- 12 weeks
- Dose
- 500 mg/day
- Population
- Healthy adults
- Participants
- 116
EleutheroView supplement →
Reconsider purchase·★★★★★
How we scored this▸
- Eleuthero has not been studied much on its own, so we don’t know how well it works by itself.
- In people with the flu, a product combining eleuthero (20–30 mg) with another herb called andrographis (178–266 mg), taken three times a day for 3–5 days, helped symptoms improve faster than amantadine (a flu medicine).
- This product also lowered the chance of problems after the flu, like sinus infections or bronchitis.
- It’s still unclear whether these benefits came from eleuthero, andrographis, or both working together.
Browse 1 study
RCTA randomized, controlled study of Kan Jang versus amantadine in the treatment of influenza in Volgograd2003n=540
In influenza patients, Kan Jang (Andrographis fixed combination including eleuthero) shortened sick leave and reduced post-influenza complications versus amantadine in two Russian RCTs (540 and 66 patients).
- Effect
- Benefit
- Population
- Patients with influenza
- Participants
- 540
GarlicView supplement →
Reconsider purchase·★★★★★
How we scored this▸
- In older adults living in care homes, taking one daily capsule of garlic and onion extract for 9 months cut flu-like illnesses by two-thirds compared to placebo.
- The treated group also had fewer symptoms and shorter sick days.
- Garlic and onion naturally boost immunity and help fight infections.
- This supplement may help protect older people from common colds and respiratory infection.
Browse 2 studies
Beneficial Effects of Daily Consumption of Garlic and Onion Extract Concentrate on Infectious Respiratory Diseases in Elderly Resident Volunteers2023n=65
In a 36-week trial of 65 elderly care residents, daily garlic-and-onion extract concentrate reduced incidence of infectious respiratory diseases versus placebo.
- Effect
- Benefit
- Duration
- 36 weeks
- Population
- Healthy adults
- Participants
- 65
RCTSupplementation with aged garlic extract improves both NK and γδ-T cell function and reduces the severity of cold and flu symptoms: a randomized, double-blind, placebo-controlled nutrition intervention2012n=56
In a 90-day double-blind RCT of 120 healthy adults, 2.56 g/day aged garlic extract improved NK and gamma-delta T cell proliferation and reduced cold and flu symptom burden versus placebo.
- Effect
- Benefit
- Dose
- 2.56 g/day
- Population
- Healthy adults
- Participants
- 56
TheanineView supplement →
Reconsider purchase·★★★★★
How we scored this▸
- It is unclear if taking L-theanine alone helps prevent the flu.
- One early study found that taking a combination of green tea extract and L-theanine every day for 5 months lowered the chance of getting flu diagnosed by a doctor compared to no treatment.
- But the combination did not stop flu infections confirmed by lab tests.
Browse 1 study
RCTEffects of green tea catechins and theanine on preventing influenza infection among healthcare workers: a randomized controlled trial2011n=197
In 197 healthcare workers over 5 months, green tea catechins (378 mg/day) plus theanine (210 mg/day) lowered clinically defined influenza versus placebo (4.1% vs 13.1%; adjusted OR 0.25).
- Effect
- Benefit
- Duration
- 5 months
- Dose
- 378 mg/day
- Population
- Older adults
- Participants
- 197
- Ages
- 20+
AloeView supplement →
Do not purchase·★★★★★
How we scored this▸
- It is uncertain if aloe alone helps prevent or reduce flu symptoms.
- One small study showed that a supplement containing aloe, rosemary, and poria mushrooms taken before and after the flu vaccine did not improve immune response or reduce cold and flu symptoms compared to a placebo group.
Browse 1 study
RCTHealthy adults supplemented with a nutraceutical formulation containing Aloe vera gel, rosemary and Poria cocos enhances the effect of influenza vaccination in a randomized, triple-blind, placebo-controlled trial2023n=25
In an RCT of 25 adults per group aged 40-80, UP360 (Aloe, rosemary, Poria) altered immune markers after influenza vaccination but did not change respiratory illness symptoms or quality of life versus placebo.
- Effect
- No Benefit
- Population
- Adults
- Participants
- 25
- Ages
- 40–80
Evidence visualised
Same ratings as above, aggregated so you can see coverage and imbalance.
| Supplement | DEX | Studies | Meta-analyses | Share |
|---|---|---|---|---|
| Elderberry | ★★★★★68% | 5 | 0 | 21% |
| Green Tea | ★★★★★52% | 5 | 1 | 21% |
| Vitamin D | ★★★★★48% | 4 | 0 | 17% |
| Brewer's Yeast | ★★★★★44% | 2 | 0 | 8% |
| Garlic | ★★★★★44% | 2 | 0 | 8% |
| Panax Ginseng | ★★★★★56% | 2 | 0 | 8% |
| Aloe | ★★★★★32% | 1 | 0 | 4% |
| Eleuthero | ★★★★★44% | 1 | 0 | 4% |
| N-Acetyl Cysteine (NAC) | ★★★★★56% | 1 | 0 | 4% |
| Theanine | ★★★★★44% | 1 | 0 | 4% |