Codeine is typically detectable in urine for 1 to 5 days after your last dose, depending on factors like how much you took, how often you used it, and the sensitivity of the test. The drug itself clears your bloodstream relatively quickly, with a half-life of about 3 to 3.5 hours in adults, meaning half the dose is eliminated roughly every three hours. But your body converts codeine into other compounds, including morphine, and those metabolites can linger longer than the original drug.
How Your Body Processes Codeine
Once you take codeine, your liver breaks it down through several pathways. The most important one converts about 5% to 15% of the dose into morphine, using a liver enzyme called CYP2D6. That morphine is what actually provides pain relief. The rest of the codeine is processed into inactive compounds that your kidneys eventually flush out.
Because codeine’s half-life is 3 to 3.5 hours, most of the parent drug is gone from your blood within about 15 to 18 hours. But morphine has its own half-life (up to nearly 7 hours in some people), and morphine itself gets broken down into additional metabolites. This chain of conversions is why drug tests can pick up traces well after you’ve stopped feeling any effects.
Detection Windows by Test Type
Different drug tests look for codeine and its metabolites in different biological samples, and each has its own detection window.
- Urine: 1 to 5 days. Most standard workplace and clinical drug screens use urine. Federal workplace testing programs screen for codeine and morphine together at an initial cutoff of 2,000 nanograms per milliliter (ng/mL). A single low dose may clear in 1 to 2 days, while repeated use can push detection closer to 5 days.
- Oral fluid (saliva): Up to about 48 hours. Saliva tests use much lower cutoff levels (30 ng/mL for the initial screen, 15 ng/mL for confirmation), which makes them sensitive despite the shorter window.
- Blood: Roughly 12 to 24 hours. Blood tests reflect what’s actively circulating in your system and have the shortest practical detection window.
- Hair: Up to 90 days, in theory. Hair testing works by detecting drug residues trapped in the hair shaft as it grows, with roughly one inch of hair representing about 60 days of history. However, hair assays are not always designed to detect codeine specifically, and this method is less commonly used for opioid screening.
Why Detection Times Vary So Much
The range of 1 to 5 days for urine is wide because no simple formula connects the amount you took to what shows up in a sample. Multiple factors influence how quickly your body clears codeine and its metabolites.
Frequency and dose matter. A single therapeutic dose leaves your system faster than days or weeks of regular use, because repeated dosing allows metabolites to accumulate in your tissues. Urine concentration also plays a role: if you’re well hydrated, your urine is more dilute, potentially lowering the concentration of metabolites below the test’s cutoff. If you’re dehydrated, the same amount of metabolite appears at a higher concentration.
Age, body composition, and overall metabolism all contribute as well. Younger, healthier adults with normal liver and kidney function tend to clear the drug faster. The timing of your last dose relative to when the sample is collected can shift results significantly, even between two people who took the exact same amount.
Genetics Can Speed Up or Slow Down Clearance
Your genetic makeup has a surprisingly large effect on how you process codeine. The CYP2D6 enzyme that converts codeine to morphine comes in several genetic variants, and roughly 5% to 10% of people of European descent fall at one extreme or the other.
If you’re what’s called a “poor metabolizer,” your body converts very little codeine into morphine. You produce fewer active metabolites overall, which could theoretically shorten the detection window for morphine in a drug test. The tradeoff is that codeine provides little to no pain relief for these individuals.
At the other end, “ultra-rapid metabolizers” convert a much higher percentage of codeine into morphine than average. This means more morphine and morphine-derived metabolites circulating in the body, which can extend detection times and also raises the risk of serious side effects, even at normal doses. Case reports have documented severe respiratory depression in ultra-rapid metabolizers taking standard codeine prescriptions. Most people fall somewhere in the middle (“extensive metabolizers”) and process the drug at a predictable rate.
Kidney and Liver Health
Since your liver does the work of breaking codeine down and your kidneys handle excretion, impairment in either organ can slow the process considerably. In studies comparing people on dialysis with healthy volunteers, the half-life of codeine was significantly longer in those with kidney dysfunction. Metabolites that would normally be filtered out can accumulate, extending both the drug’s effects and the window during which a test would come back positive.
Liver disease has a similar impact. Because all three of codeine’s metabolic pathways run through the liver, reduced liver function means slower conversion and slower clearance. If you have known kidney or liver problems, codeine will stay in your system longer than the standard timelines suggest.
What Drug Tests Actually Detect
Standard urine drug screens don’t just look for codeine itself. They screen for a class of compounds, typically flagging both codeine and morphine together in the initial immunoassay. If that initial screen is positive, a confirmatory test identifies the specific substances present.
This matters because even after codeine itself has been metabolized, its morphine byproduct (and morphine’s own downstream metabolites) can still trigger a positive result. In many situations, the parent drug is undetectable within 24 hours, but metabolites remain for an additional few hours to a few days. So a positive test three or four days after your last dose doesn’t necessarily mean codeine is still active in your body. It means your kidneys are still flushing out the remnants of its breakdown.
It’s also worth noting that codeine can cause a test to show positive for morphine, and morphine itself gets further converted into hydromorphone in small amounts. This chain of metabolites can sometimes create confusing results if you or a clinician aren’t aware of what was originally taken.