Common mullein was imported into the United States early in the 18th century and cultivated for its medicinal properties and use as a piscicide. (1) It is common in all the states, and in Canada. Due to phenotype variations within the species, V. thapsus has the ability to grow in a wide range of habitats and conditions.
Mullein is usually a biennial. First year plants are a basal rosette of soft, fuzzy leaves. Because they are so soft, the leaves are also called flannel leaf and bunny’s ears. In its second year, mullein spikes and flowers, and can grow quite tall, about 6-8 feet. The second year plants are easy to identify even from far away, and in my opinion can be rather handsome.
Mullein is best known as a treatment for respiratory complaints such as chest colds, bronchitis, and asthma. The leaves and flowers contain mucilage, which is soothing to irritated membranes, making it helpful for sore throat. The saponins it contains work as an expectorant. Mullein soothes digestive upsets and relieves stomach cramps. It can be made into a tea; the flowers make a sweeter tea than the leaves, which are slightly bitter. Strain the tea through a coffee filter to remove stray hairs.
Native Americans also drank a decoction of the roots for cough, or smoked the dried leaves to treat asthma. Leaf poultices soothe skin rashes, bruises, and rheumatic pains. Mullein’s antibacterial properties inhibit mycobacterium, the bacteria which cause tuberculosis. It supports thyroid function, relieves migraine pain, and has a calming effect as a sleep aid. Used as a compress, mullein is a soothing treatment for cold sores or hemorrhoids. As a diuretic, it is helpful long-term for the prevention of bladder infections. For incontinence, and bedwetting in children, mullein helps by strengthening the muscle at the base of the bladder. An infusion of mullein root has a moisturizing and lubricating effect on the synovial membranes, helping with inflammation and pain in the spine and joints.  The flower oil has been used to treat earache ( especially when combined with fresh garlic), as well as mouth and gum ulcers.
To make mullein flower oil, fill a small jar with fresh mullein flowers. Letting them wilt for a few hours is helpful as it reduces their moisture content. Mash them slightly, and fill the jar with olive oil, submerging them completely. Stir to make sure there are no air bubbles. Cap the jar and place it on a sunny windowsill for at least five days, or up to a month. Then, strain the mixture and pour the oil into another jar. Mullein flower oil will keep for up to two years in a cool place.
The useful parts of mullein (flowers, leaves, and roots) have almost no toxicity. Mullein is effective and safe. Only the seeds should be avoided.
cited sources: 1. herbcraft.org