Sambucus nigra (elderberry) has a long tradition of use for colds and flu-like symptoms, and in recent decades, several scientific studies have investigated its antiviral properties. Laboratory research indicates that extracts of elderberry can inhibit replication of influenza viruses and may block viral attachment to cells. Randomized, placebo-controlled clinical trials—though limited in number and scale—have found that elderberry extract may reduce the duration and severity of cold and influenza symptoms. For example, a 2004 double-blind study reported that adults with influenza who took elderberry syrup experienced symptom relief about four days earlier than those given placebo. Another 2016 meta-analysis of randomized trials concluded that elderberry supplementation appears to reduce upper respiratory symptoms in both cold and flu.

However, limitations in the quality and size of clinical trials mean that while the evidence is promising, it is not definitive. Most studies have small sample sizes, and there is a need for larger, high-quality trials to confirm efficacy and safety. Nevertheless, based on current evidence, elderberry is considered to have some scientific validation for use against colds, with its antiviral and immune-modulating effects being the likely mechanisms of action.