Take 600mg codeine don't works because the effects of codeine are the action of the morphine into is metabolized a 10% of the codeine taken but this pass from codeine to morphine only happens until 400mg codeine, more than 400mg has no more effect than 400mg
Codeine is a classic narcotic although a minor narcotic, acts like morphine, heroin or methadone but tramadol is an atypical opioid is a narcotic a bit less potent than codeine but too produces higher levels of serotonin and norepinephrine, are different effects