Lean, the drink made by mixing prescription codeine-promethazine cough syrup with soda, typically stays detectable in urine for 1 to 2 days after your last use. The exact window depends on the type of test, how much you drank, and how quickly your body processes the drugs. Codeine is the component most drug tests target, and it clears faster than many people expect, though hair testing can pick it up for months.
How Your Body Processes Lean
Lean contains two active drugs: codeine and promethazine. They leave your system at different rates. Codeine has a half-life of roughly 1.5 hours, meaning half the drug is eliminated from your blood in that time. After about 6 to 9 hours, most of the codeine itself is gone from your bloodstream.
Promethazine, the antihistamine that causes the drowsy, sedated feeling, sticks around longer. Its half-life ranges from 9 to 16 hours. That means promethazine can take 2 to 3 days to fully clear from your body, though standard drug panels don’t test for it.
Your liver does most of the work breaking down both drugs. About 80% of codeine gets converted into inactive byproducts that are flushed out through urine. A smaller portion, roughly 5 to 10%, gets converted into morphine, which is actually the compound responsible for codeine’s painkilling and euphoric effects. This matters for drug testing because many screening panels look for morphine as a marker of codeine use.
Detection Windows by Test Type
Urine
Standard urine drug screens detect codeine for 1 to 2 days after use. Urine tests are the most common method used for employment and legal screening. The initial screening cutoff for codeine and morphine is 2,000 nanograms per milliliter under federal testing guidelines, with confirmatory tests set at the same threshold. Because the cutoff is relatively high, trace amounts from a single small dose may fall below detectable levels sooner than 48 hours.
Oral Fluid (Saliva)
Saliva tests can detect codeine for roughly 1 to 2 days, similar to urine. However, the cutoff concentrations are much lower: 30 nanograms per milliliter for the initial screen and 15 nanograms per milliliter for confirmation. Those lower thresholds mean saliva tests can pick up smaller amounts of codeine that a urine test might miss.
Blood
Blood tests have the shortest detection window. Codeine is generally undetectable in blood within 24 hours of use. Blood testing is uncommon for routine drug screens and is mostly reserved for emergency medical situations or accident investigations.
Hair
Hair follicle testing has the longest reach. Research has shown that codeine can be detected in hair for at least 10 weeks after a single dose, and at higher concentrations after repeated use. Codeine reaches the hair root within 30 minutes of ingestion and becomes locked into the strand as it grows. A standard hair test analyzes 1.5 inches of growth, which covers roughly 90 days of history. Hair tests won’t typically catch use from the most recent 7 to 10 days, since it takes time for the hair to grow past the scalp.
Why Clearance Times Vary From Person to Person
The 1 to 2 day window for urine detection is an average. Several factors can push that window shorter or longer.
Your liver enzyme profile plays a major role. A specific liver enzyme called CYP2D6 is responsible for converting codeine into morphine. People carry different genetic versions of this enzyme. “Ultrarapid metabolizers” have extra copies of the gene and convert codeine to morphine faster and more completely, which can change the ratio of metabolites that show up on a test. On the other end, “poor metabolizers” lack functional copies of the enzyme and process codeine much more slowly. Roughly 5 to 10% of people of European descent fall into the poor metabolizer category, and the percentage varies across ethnic groups.
Liver and kidney health directly affect how long any drug lingers. Both organs are responsible for breaking down and excreting codeine and its byproducts. Liver disease slows metabolism, and kidney dysfunction reduces excretion, either of which can extend detection times. Aging also reduces the efficiency of both organs, meaning older adults generally clear codeine more slowly than younger ones.
Frequency and amount of use matter as well. A single cup of lean will clear faster than several days of heavy use. With repeated dosing, codeine and its metabolites can accumulate in your system, potentially extending the urine detection window beyond the standard 2-day estimate. Body fat percentage, hydration levels, and overall metabolic rate also play smaller roles.
What Drug Tests Actually Look For
Most standard drug panels include an opiate immunoassay, which is designed to flag morphine and codeine together. Codeine triggers a positive result on this screen because the body converts a portion of it into morphine. If the initial screen comes back positive, a confirmation test identifies the specific opiates present and their concentrations.
Promethazine is not included on standard drug panels. It’s an antihistamine, not a controlled substance in most testing contexts, so it won’t trigger a positive result on its own. The drug test concern with lean is entirely about the codeine component.
One detail worth knowing: poppy seeds can also cause a positive opiate screen. If you test positive and claim poppy seeds as the cause, confirmatory testing can often distinguish the metabolite pattern of food-derived opiates from pharmaceutical codeine, though this isn’t always straightforward.
Risks of Repeated Use
Beyond detection windows, the way your body handles codeine carries real safety implications. People who are ultrarapid metabolizers face a heightened risk of morphine buildup even at normal doses, which can cause dangerously slowed breathing. The FDA has flagged this risk specifically on the codeine drug label, noting that ultrarapid metabolizers may experience life-threatening respiratory depression. Most people don’t know their metabolizer status, which makes dosing unpredictable.
Combining codeine with promethazine amplifies the sedative effect, since both drugs suppress the central nervous system. Adding alcohol, which many lean recipes involve, compounds this further. The liver processes all three substances, and overwhelming it slows clearance of each one, extending both the effects and the detection window.