He had a disorder.
I believe Shiho used Shiwoon because he was "Convenient". She was jealous of 9ad going after the other female teacher and knew he would come to the aid of his disciple. Now his convenience comes into play because he has a similiar vein blockage disorder as Sosul(he has 3 blocked and Sosul 9). Shiho took advantage of a good opportunity to achieve her personal goals and validate part of her mission(the pill being able to cure the blockage).
I would think with the data obtained, since Sosul's condition is much worse, and it is confirmed Shiwoon's blood heals the condition, They would either use an animal or plant that could handle absorbing it, then feeding Sosul blood or part of the plant. Could also be that 9ad took a pill and is probally donating blood to her on a regular basis.
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