Why does codeine increase my appetite ?

NO IDEA: at all! Most commonly OPIATES DECREASE the appetite! Consult with the Prescriber!! Hope this helps! Dr Z

I can only guess: Sometimes appetite is increased when anxiety is less and opioids are known to reduce anxiety. While codeine is a "mild" opioid some people are quite sensitive. That's my best guess. Careful though, because I think this sensitivity to codeine might put you at greater risk of becoming addicted to it.