For me personally it works as horrible stimulant. I was once in the Cardiac IC on IV with Nitroglecerin, which gives bad headaches. They gave me a pill to help headache with codein in it.
Well, 1/2 hours later I got so irritable, restless, shaking of hands and feet, very aggravated without any reason, and the whole body itched with red patches on it.
This is exactly worked on me as if I had any stimulant include coffein. My body does not take well stimulants of any kind. I will never be able to have a regular cup of coffee or tea. Tried and it makes me very sick.
Since than DR put on my chart "severe allergic to codein". Actually I tried once (forgot that this meds has codein in it) to take my husband's med from migrane headache and had same reaction.
But everybody is different though.
