After having an inguinal hernia operation about a year ago, I was given Tylenol with codeine to use for pain as needed. I found that even with episodes of similar pain level, it would be very beneficial and long-lasting on some days; very beneficial but only briefly on some days; and no effect whatsoever (like placebo) on some days (most, in fact). Back at the time the surgeon said he had never heard of such variation, and that I must be mis-reading the level of pain. But not so. In the past I had been prescribed the same drug after different procedures, and the effect was *always* predictable -- very beneficial and long-lasting (maybe four hours or until sleep). Why would this change? If it were due to metabolism changes with aging, that still wouldn't explain the major, unpredictable day-to-day variation, would it? Everything was pretty consistent in terms of diet, stress levels, etc. Any ideas? Does this suggest that some sort of abnormality has (or had) developed? Thanks.