@turkay1-- The side effects will depend on the medication and the dose. But the procedure itself isn't painful. It hasn't been for me anyway.
I get regular IV pushes because I have chronic fatigue syndrome. I have not had any adverse side effects from the procedure and it hasn't been irritating or painful. Even my three year old son had to get a Vitamin K IV push once and he did just fine too.
What they do is they go into the vein with a butterfly needle and tape it on your arm or hand. And then the medication is pushed very slowly into the bloodstream.
Of course, an IV push is preferred in certain cases and medications. But personally, I prefer it over an IV drip which takes way too long.