oleander soup

Hello I am new to the group and in the last couple of days I made up my first batch of Oleander soup. And I am quite curious about the taste, I bought some plants at a local nursery and they claim to only use galic and hot peeper mixes to spray their plants. The taste of my soup is very bitter and it mskes your tongue slightly numb, is this normal? I will be using the soup for my dog with osteosarcoma and my self for hep c. And do not want to poison either one of us. I followed the directions very closely and filtered 4 times with 6 coffee filters each time. any help on this would be great. Thanks, Scroller