herb · for frequent colds
Garlic
Stirs up your immune cells and appears to cut how often you catch one.
Say that in clinical terms
Allicin stimulates immune cell function and reduces cold incidence through antimicrobial and immunomodulatory effects.
How strong is the research?
Solid evidence
Only one studyA different form was studied
1 paper read, 1 supporting.
Who was studied: 146 healthy UK adults over one winter. Not tested in the elderly or immunocompromised.
How much to take
daily
180–360 mg
Prophylactic use reduces cold incidence by ~60%. Use aged extract for better tolerability.
Before you take it
- No NIH ODS Tolerable Upper Intake Level (UL) established for aged garlic extract as a preparation; most clinical trials use 600–1,200 mg/day without reported serious adverse events at these doses.
- Antiplatelet activity: may potentiate bleeding risk when combined with warfarin, aspirin, or clopidogrel — INR monitoring recommended.
- Significantly reduces plasma saquinavir (HIV protease inhibitor) levels — clinically important drug interaction; concurrent use should generally be avoided.
- Additive blood-pressure-lowering effect with antihypertensive medications; risk of clinically significant hypotension, particularly at higher doses or in susceptible individuals.
- Timing with antibiotics: take at least 2 hours before or 4–6 hours after tetracyclines or fluoroquinolones to avoid absorption interference (NIH ODS guidance; note asymmetry — 2h before vs 4–6h after).
- Common mild adverse effects include halitosis, heartburn, and GI discomfort; aged garlic extract is generally better tolerated for odor than raw garlic or allicin preparations.
What we make of it
Our mechanism credits allicin, which aged garlic extract does not contain.
The detail
Aged garlic extract is aged precisely because that process converts allicin into other compounds. Attributing the effect to allicin describes a different product from the one being studied.