The most widely applied medicinal use of sugarcane is to sweeten bitter-tasting medication. Many say that for this purpose only 'Kea' or 'Opukea' was traditionally used. Perhaps this is because these canes have the whitest flesh and therefore the purest juice (although 'Kea' is also considered the most ancient of the Hawaiian canes and may relate to this usage). For instance, the fruit of the noni is used to expel the placenta after birth, and 'Kea' is used to wash it down. 'Kea' can be used to sweeten a range of medicines, such as the ‘apu kowali or ‘apu la‘au ho‘onahā used as purgatives or the ‘apu ho‘omomona used to combat thinness and lack of energy.
In addition to sweetening bitter-tasting medicines, cane juice is an active ingredient in curative formulas. The most popular application was for deep cuts, the sugar crystals dry out a wound and prevent the growth of infection-causing bacteria. A short story is related in Fornander about using sugarcane as a mixture to form a salve or ointment:
This cane was discovered by Kulua and Paiaalani. While Kulua was lying very sick with chills and with sores covering his body, Paiaalani came to him and asked, “Why are you lying in the house these days and not going out? … That disease is easily cured if you will get that cane called Uleohiu; boil it in hot water, drink some, rub some on your skin, and you will be cured.
Sugarcane varieties are said to vary in their therapeutic properties. Kahuna hāhā, who diagnose and treat sicknesses and pain, considered 'Kea', 'Honua‘ula', 'Lahi', and '‘Ainakea' the best for medicinal purposes. 'Lahi' is the primary variety used in diagnostics, in which ritualistic practices and movements utilizing the cane are used to divine the ailment of patients and the potential outcome of treatments. One text indicates one such protocol:
The sugar cane [stalk] was pulled apart (‘ume) by the kahuna and examined. If the overripe part (kō pala) of the sugar cane was in the left hand and the healthier part (kō maika‘i) in the right, then the kahuna deemed the patient to be ‘alive.’ However, if the opposite occurred, then the patient was deemed ‘dead.’
All kō varieties are used by various practitioners, with some favored over others in particular lineages of practice or specific districts. For instance, some lapa‘au practitioners use 'Manulele,' although kahuna hāhā will not. Other times, distinct varieties of cane are necessitated, often for their religious significance. '‘Ele‘ele' or 'Māikoiko' were the only cane varieties used for treatments of tuberculosis. Most say that it is okay to substitute a similar variety if the cane of choice cannot be found, a popular example being using 'Pāpa‘a' in place of 'Honau‘ula.' Canes are used in mixtures to treat asthma, deep lacerations, sprains, pain/shock, illness of a weak heart, running sores, thrush, and gonorrhea, in addition to native illnesses such as make uila wale and pā‘ao‘ao. Concoctions will utilize specific parts of the cane plant. The very young buds of sugarcane are the most common ingredient, but occasionally a tincture will call for the juice, the leaves, or even the roots.
Many treatments require purgatives. An "opening," or a total purging (emetic, purgative and enema), is often administered to prepare a patient for the positive effects of medicines to follow. Purgatives are used to treat cramps, stomach ailments, and other more severe diseases. A typical purgative mixture includes the pounded kowali (Ipomoea indica) root, raw eggs, mashed kukui nuts, noni fruit, and the juice of the sugarcane. Kō can be used alone as an emetic in large quantities; however, it is typically combined with other ingredients.
The very young buds are a good medicine for pouring on deep cuts and wounds. One such recipe calls for four young kō buds, two kowali pehu vines, and one-quarter ‘apu (coconut-shell cup) of pa‘akai (sea salt). The ingredients are pounded into a fine mash and bundled up inside of kī leaves and broiled until cooked. The resultant salve can be applied to wounds, fractures, and internal injuries as well. This medicine is to hasten the healing process but also to reduce the formation of scars.
The stalks of the sugarcane are used to treat a range of infections. A medicine concocted for the treatment of hilo or waikī uses four segments of '‘Ainakea' and the meat from one ripe coconut. These are mashed, strained, and mixed with the slimy sap of the hau ka‘eka‘e (Hibiscus tiliaceus) and applied to the genitalia before and after urination. A similar concoction was made with 'Pale ‘Ōpua' to cure the female version of the sickness, kohepopo.
Sugarcane was often used in pregnancy, both in topically applied salves and lubricants, and ingested concoctions. 'Māikoiko' is the most commonly used cane in childbirth. Sugarcane juice can be used to keep the mother energized and mixed with other concoctions to induce labor. Sugarcane juice is also a key ingredient, along with the slimy sap of the hau ka‘eka‘e and other plants, in the lubricating liquids made to help with delivery. Kō was also often used in post-natal treatments, such as to increase mothers' supply of milk. One such treatment is ‘apu ho‘opa‘a, which uses juice from aerial roots of the hala, juice from the stalks of the sugarcane, and several drops of sap from the flower of 'Iholena' banana all mixed with mashed ‘uala.
Wai kō (sugarcane juice) was particularly prevalent in treating infants. Warm, toasted wai kō was said to be the saving grace of young babies when nothing else would work. The warmed juice of 'Honua‘ula' is supposed to be the only cure for infants who have contracted make uila wale.