In a nutshell, the administration of herbal medicines and drugs is not as extensive as that of other categories of drugs in which there are a myriad of ways to take and/or abuse the drug. If one were to consider the fact that some of the most powerful substances of abuse are extracted from plants, such as cocaine (Erythroxylum coca), marijuana (Cannabis sativa), peyote (Lophophora williamsii), and tobacco (Nicotina tabacum), then one’s view of the previous statement may be somewhat altered (Hanson, 2012). However, as the book mentions, these substances are mentioned elsewhere in the book in the contexts of other drug categories, and need not be mentioned in broad detail in this context.
Excluding the various means of administrations of drugs such as marijuana, cocaine, and other drugs that can be extracted from plants (such as snorting, smoking, injecting, etc.), the majority of the drugs that will be discussed here are administered orally, applied to the skin, and in some cases, inhaled. To provide a few examples; herbs such as acai, cinnamon, cranberry, garlic, ginger, ginseng, licorice root, and soy are all substances that fall under this category and are commonly used to make teas, juices, extracts, and, in some cases, in preparation for external use. Examples of external use in herbal drugs stem from the use of aloe vera as topical ointment, the Echinacea plant (which can treat upper respiratory tract infections such as the common cold), peppermint oil which can be applied to the skin to counteract heartburn, and sage, which is available as dried leaves, liquid extracts and sprays, and essential oils and used as a folk remedy for mouth and throat inflammation, indigestion, and excessive sweating; to improve mood; and to boost memory or mental performance (“Herbs at a Glance”, 2013).
Lastly, to mention a few recognizable names, ginseng, glucosamine, chamomile, green tea, dandelion, and lavender also fall under this category and serve various purposes ranging from an increase of energy (ginseng), to arthritis relief (glucosamine), even to aromatherapy (lavender) in which the scent of the essential oil from the flowers is inhaled, but can also be taken orally and applied to the skin to help with a wide variety of cases, even including hair loss (“Herbs at a Glance”, 2013). In most cases, these herbal drugs are taken orally and more often than not are administered in an edible fashion such as being squeezed to be used as fruit or made into tea, or used in such a fashion as to treat a sickness or condition such as asthma, eczema, premenstrual syndrome, rheumatoid arthritis, migraine, menopausal symptoms, chronic fatigue, irritable bowel syndrome, and cancer, among others ("Herbal medicine," 2011).

Herbs at a Glance (2013, 03 06). Retrieved from http://nccam.nih.gov/health/herbsataglance.htm
Herb and supplement use in the US adult population (2013). Retrieved from http://www.sciencedirect.com/science/article/pii/S0149291805002833