DD had to take iron supplements, three syringes worth of liquid, twice a day for three months from the age of 17 months. For three days we tried forcing her and it a nightmare for everyone. It was very stressful for her (by the second day she would point to where the bottle was kept and scream 'no no no no' even when we made no attempt to give it to her), she was very difficult to hold still (13 kilos of thrashing toddler is no joke) and most of the medicine was getting sprayed everywhere and the rest she spat out.
So I did what I do with the dogs, operant conditioning. Two slight variations on this depending on how much your DC understands:
Use a special implement for the medication, a syringe is good or a special spoon you only use for that. Buy the most wonderful stickers you can find and don't give them for anything else. If the child understands the idea show him the stickers and as soon as he goes to take them say that he has to take the syringe in his hand before he can have a sticker (ask for an action that he is likely to want to do, like touching the syringe, not one that he likely to refuse, like taking the medicine. What you want is behaviour you can reward so set aside the final goal for a moment. If he refuses to hold the syringe ask him to touch it or even just look at it and work up from there). As soon as he does this, praise profusely and allow him to pick a sticker making a huge fuss over the whole thing (if your DC is not interested in stickers find something else to motivate him. Food may be problematic as you will need a lot of it).
The variation here is that if the child is too young to understand the interaction you need to show them. So as they reach for the stickers, put the syringe in the way but try not to force the issue. The child has to chose to touch the syringe.
Build from there by asking for more and quickly rewarding progress. So ask for the syringe to touch the mouth, etc. If things go wrong, revert to an earlier behaviour the child is willing to do.
It sounds like this will take weeks to do but DD took her morning medication the first time I tried it within 10 minutes, she was a lot faster by the same evening and witing a few days she would immediately allow the syringe in her mouth without any of the first steps. By the end of the three months she no longer needed the stickers as the association had been made and it's useful for giving medicines in the future with the same syringe.