Is the medicine a pill?? If so try wrapping Ozzy in a towel, much like a burrito with only his head showing. Sit in a chair and place wrapped Ozzy between you and the arm of the chair with your left arm around him. Now he can't go anywhere. To open the mouth you use the left hand to open the upper jaw and your third finger of your right hand to ease down on the lower jaw. The pill should be between your thumb and second finger of the right hand. With the mouth open, shove the pill in as far back as you can get it, then close the mouth quickly. Rub under the chin or softly blow in the nose and the cat should swallow. If Ozzy licks his lips, that means the pill is down.

At least, that's how I do it. If it's liquid then the same thing applies but you ease the syringe in the side of the mouth and administer that way. A little at a time otherwise he might choke.

Other people will have more suggestions I'm sure. Good luck.