We used to have a horrible time with this. Finally the doctor just looked at us and said, you are the adults. We felt a little foolish so we went home and were loving but firm.
We explained that she had to take her medicine but as soon as she did, she could have a popsicle. Then we made up a song, Medicine-Pop, Medicine-Pop. I was holding the popsicle in my hand and once the meds were down I immediately handed her the popsicle. It worked for us anyway. I suppose it would work with any treat that the child loves but is not able to have all of the time. It would have to be something special.