Hawthorne berries regulate heart function restoring it gently to correct functioning. Anti-viral properties are NOT attributed to Hawthorne berry. Milk thistle has been shown in clinical studies to also have NO anti-viral properties. Milk thistle is used for supporting the liver and has been shown to regenerate liver cells. Studies have shown that its toxicity level is so extremely LOW that even babies can use milk thistle. An herb that DOES have anti-viral properties is Lomatium root. It is also anti-bacterial and anti-inflammatory. Lomatium root is especially useful in respiratory illness and to stimulate the immune system, in addition, it has antibiotic properties.
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To add to the answer already given, I concur that the two herbs you mentioned are not known to be antiviral. However there are many common plants which do seem to have those properties. One of the most common is ordinary tobacco. Although it has negative effects when smoked, even the smoke itself may be able to be used as an antiviral medication at some point. Early Native Americans used it as a topical application as well. The linked journal article is from a study of the use of the smoke on viral infections.
Antiviral agents act to destroy viruses in the body. Hawthorne berry strengthens the heart and circulatory system, regulates blood pressure and improves coronary blood flow. Milk Thistle herbs have shown potent liver protective properties as well as the ability to help protect against environmental toxins and pollutants. Clinical trials performed in countries outside the US have shown some of these herbs to detoxify dangerous carcinogens, act as free radical scavengers, stimulate liver repair, normalize liver functions, counteract the effects of a wide variety of poisons, alter the membranes of hepatic cells which inhibits the passage of toxins, increase cellular regeneration by stimulating protein synthesis and protect against depletion of the antioxidant gluthione in liver cells.
Milk Thistle is a natural liver detoxifier. It is one of the most widely studied herbs and should be considered a modern necessity. Milk thistle, the liver cell regenerator, aids in the production of new liver cells which help replace old & damaged ones.