If we allow for 'not mainstream medicine', why then are they stopping at those three? Why not include the spells and potions that might include pepper? Why not the treatments you or I could just make up on the spot in a work of fiction? If we expand the definition of medicine to include nonsense, the term would lose all meaning. As a society we demand medicine be 'things proven to work' and all those things they list are not part of that set; they have not been proven to work, and thus not included in 'medicine'. If they were in fact proven to work, they would simply be part of mainstream medicine.
Piperine, an extract from black pepper, is known to increase absorption of nutrients in the gut. A study on PubMed shows increases of curcumin absorption by 2000% after taking piperine. Personally, I have noticed great effects when I take piperine in combination with other compounds. I got here from studying ancient Chinese medicine.