Note: Speak with your doctor before beginning any dietary supplementation. Andrographis: Boosts immune function and may help prevent cold when taken for a few months. Echinacea: Some studies have shown that it can help to speed recovery from colds by 10-30%. Garlic: This veggie, when consumed crushed and raw, is shown to boost the immune system and can potentially help fight viruses. Ginseng: Ginseng has an immune-boosting effect. Thuja: Can help treat upper respiratory tract infections, loosen phlegm, and boost immune function. Vitamin C: Studies have shown that it can boost the immune system and help to speed recovery from colds. Wild Indigo: There is some evidence to show that this supplement can help to treat colds, but not enough information is known about how it works. Zinc: The latest research shows that zinc can help to speed recovery from the upper respiratory symptoms of a cold.