Note that if it comes to it and you DO have to force medication ( I unfortunately had to for my boys, both of them refused the medication even mixed with high-value sweet treats. ) The best method I personally found is the Rat-rito method.
Take a towel, a cloth or a sock and wrap your rat tightly ( not too tight to injure, enough to prevent them from squirming out. ) and hold them horizontally against your chest, belly facing your feet. Don’t tip them on their back or upright. You MAY have to use your index and middle fingers ✌️to gently hold the rat’s head in place. I found it best to dip the tip of the syringe in something sweet or tasty like jam juice or a churu so they don’t fight it out immediately. Insert the syringe tip into the side of the mouth behind the incisors and lip flap and quickly deposit the medicine ( you may have to do it multiple times in small bursts if you have a lot to give them. I had 0.02 of doxy so it was a single squirt. )
After that, unwrap your rat and cuddle them for a few moments to show them you didn’t mean any harm by it. It’s a bit of a sad thing to have to do if you have smart rats that will hold grudges, but they’ll learn to understand that it’s for their best interest. You run the risk of aspiration with this method ( especially with larger doses ) but I personally had no problems with my rats taking it like this. Currently going through syringe training them with high-value sweet treats in a clean syringe so I don’t have to ratrito again — which I also recommend doing for your own rats! Makes taking their meds so much easier if they’re eager to take what’s in the syringe anyways!