So, FWIW, I don't know your grandchild's temperament beyond not wanting the medicine, but something that worked for us around that age required a bit of a deal (I understand the warning about negotiating with terrorists, but this was presented as an either/or and curiousity always won out.)
The child could either take the medicine as is, administered by the adult and be done OR the child could take the medicine as is, administered by the adult and then assist in the creation of a concoction which would then by taken by teaspoonful by the adult. Now, this concoction thing involved pulling various spices and condiments from the pantry and fridge, setting them on the table and then the child would point to one. After naming it or some other small talk about it, we would put a tiny amount of those selected in a cereal bowl and kiddo would stir it and then the anticipation would set in: what kind of face is mama going to make when she tries the Old Bay seasoning, garlic powder, italian dressing combo?
It was rather hilarious and the kids outgrew the age at which medicine was a struggle, but they have fond memories of it. As a mom, it took only a little patience and desperation, but they took their medicine and got a little of their own back with the shared misery of cayenne pepper laced concoctions...