The effects of lean typically begin within 30 to 45 minutes of drinking and last roughly three to six hours, though residual drowsiness can linger well beyond that window. The range is wide because lean contains two drugs that work on different timelines, and your individual genetics can dramatically shift how much active ingredient actually reaches your brain. How you experience the comedown, how groggy you feel the next morning, and how dangerous the dose turns out to be all hinge on factors most users never think about.
What Lean Contains and How Each Ingredient Works
Lean is built around prescription cough syrup that pairs two drugs: codeine, an opioid, and promethazine, an antihistamine with strong sedative properties. Most of the “high” people describe comes from codeine, but codeine itself is not what acts on your brain’s opioid receptors. Your liver converts codeine into morphine, and morphine is the molecule that produces the euphoria, pain relief, and body heaviness associated with the drink.1The Pharmacogenomics Journal. Pharmacokinetics of codeine and its metabolite morphine in ultra-rapid metabolizers due to CYP2D6 duplication
Promethazine, the other half, amplifies the sedation. It crosses into the brain and blocks histamine receptors, which is why lean users describe an intensely drowsy, “leaning” sensation rather than the alert euphoria of some other opioids. The combination makes the experience feel heavier and more sedating than codeine alone.
When you drink lean, the codeine is absorbed through the stomach and small intestine. Peak blood levels of codeine usually arrive within one to two hours, and the conversion to morphine happens quickly after that. Most people feel the strongest effects during that one-to-three-hour window. By about four to six hours, the opioid effects are fading for most users, though individual variation is enormous.
Why the High Lasts Longer for Some People
The enzyme responsible for converting codeine into morphine, called CYP2D6, is one of the most genetically variable drug-metabolizing enzymes in the human body. How active your version of this enzyme is shapes almost everything about how lean affects you: how strong the high feels, how long it lasts, and how dangerous it can be.
About one in ten people of European descent are “poor metabolizers,” meaning their CYP2D6 enzyme barely functions. For these people, codeine produces only trace amounts of morphine, and the opioid high is weak or absent altogether.2Current Pharmacogenomics. Influence of CYP2D6 Genetics on Opioid Kinetics, Metabolism and Response They might feel the promethazine sedation but get little of the euphoria other users describe. At the other extreme, some people carry extra copies of the CYP2D6 gene, making them “ultrarapid metabolizers.” Their livers flood the bloodstream with morphine far faster and in larger quantities than normal. A case report documented life-threatening toxicity in a patient with three or more functional CYP2D6 gene copies, where the combination of rapid codeine conversion and reduced clearance caused dangerously high morphine levels.3PubMed. Codeine intoxication associated with ultrarapid CYP2D6 metabolism
Between these two extremes sits the majority of the population, with varying levels of enzyme activity. Two people drinking the same cup of lean at the same party can have vastly different experiences in both intensity and duration. The person who metabolizes codeine quickly may peak harder but come down sooner, while a slower metabolizer might feel a more gradual, drawn-out effect. There is no way to know which group you fall into without genetic testing, and most people using lean recreationally have no idea where they stand.
How Lean Slows Its Own Absorption
One underappreciated factor is that codeine itself slows down your stomach. Research using intragastric monitoring found that codeine significantly delays gastric emptying, extending the stomach’s half-emptying time to about 233 minutes compared to roughly 172 minutes with a placebo.4Neurogastroenterology & Motility. Codeine delays gastric emptying through inhibition of gastric motility as assessed with a novel diagnostic intragastric balloon catheter In practical terms, the codeine you just drank is slowing the rate at which more codeine gets absorbed from your gut.
This gut-slowing effect creates a more gradual, extended absorption curve. Instead of all the codeine hitting your bloodstream in a tight window, it trickles in over a longer period. For lean users, this is part of why the experience feels drawn out compared to taking a codeine pill on an empty stomach. The soda, candy, and sugar that lean is typically mixed with add even more volume for the stomach to process, further stretching absorption.
This delayed absorption also helps explain why many people sip lean over hours rather than drinking it all at once. The body is already processing the drug slowly, and staggered intake layers new doses on top of partially absorbed earlier ones, creating an extended plateau rather than a sharp peak and crash. The flip side is that it becomes harder to gauge how much drug is actually in your system at any moment, since your stomach may still be releasing codeine into your bloodstream from a cup you finished an hour ago.
The Promethazine Hangover
Even after the opioid effects of codeine have worn off, the promethazine component keeps working. Promethazine has a longer effective duration than codeine, and at the doses found in prescription cough syrup, it produces sedation that can persist well into the next day.
In sleep research on healthy volunteers, promethazine at 200 mg produced next-day drowsiness and hangover-like effects on 14 out of 20 study nights.5PubMed. Effects of promethazine on nocturnal sleep in normal man While recreational lean doses vary, the promethazine load from multiple cups over an evening can easily approach levels where next-day impairment is likely. This hangover is distinct from the opioid comedown. It feels more like thick-headed grogginess: sluggish reaction times, difficulty concentrating, a fog that coffee does not seem to cut through. For people who drink lean in the evening, the next morning can feel like waking up underwater.
This lingering promethazine effect is often what leads people to say the lean “lasted all night,” when in reality the opioid high ended hours earlier and what they are experiencing is antihistamine sedation. Understanding this distinction matters because the two sensations carry different risks. The opioid high is the period of greatest danger for respiratory depression; the promethazine hangover is the period of greatest danger for impaired driving, poor decision-making, and falls.
What the Comedown Feels Like
As codeine’s effects taper, typically starting around three to four hours after drinking, users often describe a gradual downslope rather than a sudden crash. The euphoria fades first, replaced by a drowsy, slightly numb feeling. Mild nausea is common as the opioid effects recede, especially in people who drank lean on a full stomach or mixed it with alcohol.
Mood changes during the comedown can include irritability, mild anxiety, or a flat emotional state. These are not full opioid withdrawal symptoms, which take regular use to develop, but rather the natural return to baseline after your brain’s opioid receptors have been artificially stimulated for several hours. The promethazine sedation typically masks some of this emotional dip, which is partly why the comedown from lean feels softer than the comedown from other opioids taken without an antihistamine.
Itching is worth mentioning because it confuses people. Codeine triggers histamine release, which can cause skin itching that sometimes persists after the pleasant effects have faded. Users occasionally interpret ongoing itchiness as a sign the drug is “still working,” but it is really just a side effect of histamine activity, not a continuation of the high itself.
How Tolerance Changes the Timeline
With repeated use, the duration and intensity of lean’s effects shift. Tolerance to opioids develops relatively quickly, and regular lean users often find that the high becomes shorter, weaker, or both within weeks of consistent use. The body adjusts its opioid receptor sensitivity downward, requiring more codeine to achieve the same morphine-driven effect.
What makes lean especially tricky is that tolerance to the euphoric effects develops faster than tolerance to the respiratory depression. A person chasing the original high by drinking more cups is stacking risk: the dose needed to feel good creeps closer to the dose that suppresses breathing. And because codeine slows gastric emptying, a larger dose does not just mean more drug in your system at once. It means the drug hangs around in your stomach longer, creating a slower but sustained delivery that can catch you off guard hours later.
Promethazine tolerance also develops, but more slowly. So a regular lean user might end up in a situation where the opioid effects are muted but the sedation is still heavy, leading to a frustrating imbalance: drowsy without much euphoria. This often drives dose escalation or the addition of other substances, both of which increase danger substantially.
How Long Lean Shows Up on Drug Tests
A question that follows closely behind “how long does the high last” is how long the drug stays detectable. Codeine and its metabolites, including morphine, are detectable in a standard urine drug screen for roughly one to three days after use. The exact window depends on how much you drank, your metabolism, hydration, and how sensitive the test is. A single evening of lean will generally clear urine detection within 48 to 72 hours for most people, though heavy or repeated use can push that window out.
Hair tests can detect codeine use for up to 90 days, though these are uncommon outside of legal or forensic settings. Blood tests have a shorter detection window, usually under 24 hours for codeine itself, though morphine metabolites can linger slightly longer in blood.
Promethazine is not part of a standard drug panel, so it typically goes undetected unless a test specifically looks for it. However, some immunoassay urine tests have been reported to produce false positives for other substances in the presence of promethazine, which can create unwanted complications even if the codeine has cleared.
When Lean Becomes Genuinely Dangerous
The combination of codeine and promethazine is more dangerous than either drug alone. Both suppress the central nervous system, and their sedative effects stack. Adding alcohol, benzodiazepines, or other sedatives to the mix compounds the risk further.
Respiratory depression is the primary cause of death in lean-related overdoses. The opioid component suppresses the brainstem’s drive to breathe, and promethazine’s sedation makes it harder for the body to compensate. People who are ultrarapid metabolizers of CYP2D6 are at heightened risk because the same dose of codeine produces far more morphine in their bodies than it would in a normal metabolizer.3PubMed. Codeine intoxication associated with ultrarapid CYP2D6 metabolism There is no external way to tell whether you carry this genetic profile without testing, and the consequences of finding out the hard way can be fatal.
Seizures are another underappreciated risk. At high doses, promethazine can lower the seizure threshold, and this risk increases when combined with other substances. The slow, sipping pattern of lean consumption gives a false sense of control, but the delayed gastric emptying described earlier means that drug levels may still be rising even an hour or two after the last sip. By the time you realize you have had too much, the peak has not yet arrived.
Codeine Versus Dextromethorphan-Based Syrups
Not all “lean” is made the same way. Some people substitute over-the-counter cough syrups containing dextromethorphan (DXM) when codeine-promethazine syrup is unavailable. The experience is fundamentally different. DXM at recreational doses acts as a dissociative rather than an opioid, producing effects more similar to ketamine than to morphine. The duration, subjective quality, and risks of a DXM-based mixture have little in common with traditional codeine-promethazine lean, and the two should not be conflated despite sometimes sharing the same street name.
This confusion matters for safety. The harm-reduction advice, the overdose risks, and the drug interactions are completely different for the two substances. Naloxone, the opioid reversal agent available at many pharmacies, can reverse a codeine overdose but will do nothing for DXM toxicity. Someone expecting opioid sedation from a DXM syrup, or someone treating a DXM overdose as if it were an opioid emergency, can make dangerous mistakes in either direction. If you are not certain which active ingredient a syrup contains, the label will tell you, and the distinction is not academic.