The inclusion of Marshmallow, traditionally used in Western herbal medicine, suggests a focus on soothing irritated throats and dry coughs, which are common symptoms of lingering coughs. This can provide comfort and relief for individuals experiencing these symptoms. Additionally, the immune support aspect of this product is beneficial for helping the body's natural defenses combat the underlying cause of the cough, which is often a viral infection like the common cold. The blackberry and vanilla flavor likely make this oral liquid more palatable, which can be particularly helpful for individuals, especially children, who may have difficulty taking medication. Overall, Duro-Tuss Lingering Cough + Immune Support Oral Liquid seems like a comprehensive solution for addressing lingering coughs while also providing immune support in a pleasant-tasting formula. (description exceeds maximum possible length)