I tried it - it works, but someone mentioned that codeine is best ingested because the liver metabolizes it to morphine. Is that correct? What about paracetamol? Since it has negative effects on the liver when ingested in large amounts, would enema help?
Enema works better for me than does ingestion. Whether the liver is involved in metabolizing codeine in an enema is the question to which you don't have the answer. But depending on this answer, I can decide whether to perform CWE or not before performing an enema. Besides, you answer without having either experience with codeine enemas or understanding of codeine metabolism.
Onset time? Of course it has to be metabolized in the liver before it gets you high. Enema would get it into your blood quicker, might hit your liver at the same time as oral ingestion. I honestly can't see there being much of a difference in potency.