Most drugs clear from your bloodstream within hours to a few days, though the exact window depends heavily on the substance, how much you used, and your body’s metabolism. Blood tests have shorter detection windows than urine tests for nearly every drug, making them better at identifying recent use rather than use from days or weeks ago.
How Your Body Clears Drugs From Blood
Every substance you consume goes through a four-stage process: absorption into the bloodstream, distribution to tissues, metabolism (mainly in the liver), and excretion (mainly through the kidneys). The liver and kidneys do the heavy lifting. Your liver chemically transforms drugs into smaller compounds called metabolites, and your kidneys filter those metabolites out through urine.
The speed of this process is measured by something called a half-life: the time it takes for the concentration of a drug in your blood to drop by 50%. A drug with a two-hour half-life will be at 25% of its peak level after four hours, 12.5% after six hours, and so on. After about five half-lives, the drug is essentially undetectable. Short half-life drugs vanish from blood quickly. Long half-life drugs linger.
Detection Windows by Substance
Alcohol
Alcohol leaves the blood at a remarkably steady rate: roughly 0.015% blood alcohol concentration (BAC) per hour for most people. That means a BAC of 0.08%, the legal driving limit in the U.S., takes about five to six hours to reach zero. Heavier drinking pushes BAC higher and extends the timeline proportionally. Some people metabolize alcohol slightly faster or slower, with elimination rates ranging from 0.01% to 0.02% per hour, but the average holds for most adults.
Cannabis (THC)
Blood tests for THC typically detect use within the last 2 to 12 hours for occasional users. THC moves out of blood and into fat tissue quickly, which is why blood detection windows are so short compared to urine. Heavy, chronic users are the exception. In those cases, THC has been detected in blood up to 30 days after the last use, because the compound slowly leaches back into the bloodstream from fat stores over time.
Cocaine
Cocaine itself stays in your blood for about 12 hours. Its primary metabolite, benzoylecgonine, remains detectable for roughly 48 hours. Most blood tests look for both, so the practical detection window is about two days.
Opioids
Opioids vary widely depending on the specific drug. Here are the general detection windows:
- Codeine: 1 to 2 days
- Heroin and morphine: up to 3 days
- Oxycodone: 1 to 3 days, depending on whether it’s an immediate or extended-release formula
- Fentanyl: 2 to 3 days
- Methadone: 3 to 4 days, and up to 14 days in some cases
- Tramadol: 2 to 4 days
Extended-release formulations generally stay detectable longer because they’re designed to release the drug slowly over many hours.
Benzodiazepines
Short-acting benzodiazepines (used for acute anxiety or sleep) are typically detectable for 3 to 5 days. Long-acting versions can show up on tests for up to 30 days. This is one of the widest detection ranges of any drug class, so knowing which specific medication is involved matters a lot.
Why the Same Drug Clears Faster in Some People
The timelines above are averages. Your actual clearance time depends on several factors that can shift the window meaningfully in either direction.
Age is one of the biggest variables. The liver’s main drug-processing enzyme system loses about 30% or more of its capacity as you get older, because the liver shrinks and receives less blood flow. At age 80, kidney clearance is typically half of what it was at age 30. This means older adults hold drugs in their blood significantly longer. On the other end of the spectrum, newborns and infants also metabolize drugs slowly because their liver enzymes aren’t fully developed yet.
Liver and kidney health directly determines clearance speed. Chronic liver disease, advanced heart failure, or kidney impairment all slow metabolism and excretion, sometimes dramatically. A drug that would normally clear in 24 hours could persist for days in someone with significant organ damage.
Genetics play a role too. Some people are naturally fast metabolizers for certain drug classes, while others are slow metabolizers. These differences are built into your DNA and can cause the same dose to produce very different blood levels in two people of the same age and weight.
Drug interactions also matter. Some substances speed up liver enzymes, causing other drugs to clear faster than expected. Others inhibit those enzymes, causing drugs to accumulate. If you’re taking multiple medications or combining substances, clearance times can shift unpredictably.
Blood Tests vs. Urine Tests
Blood testing detects drugs over a shorter window than urine testing for almost every substance. That’s because blood reflects what’s circulating right now, while urine collects metabolites that the kidneys have been filtering over hours or days. A blood test is better suited for determining recent impairment or very recent use. Urine tests cast a wider net and can pick up use from days or even weeks earlier.
Many tests look for metabolites rather than the original drug itself. Cocaine, for instance, breaks down quickly, but its metabolite benzoylecgonine hangs around four times longer. This is why detection windows often extend well beyond the time you’d actually feel the drug’s effects. The high may last an hour, but the chemical evidence remains in your blood for a day or two.
Quick Reference Table
- Alcohol: 5 to 6 hours (at 0.08% BAC)
- Cannabis: 2 to 12 hours (occasional use), up to 30 days (heavy chronic use)
- Cocaine: 12 hours (parent drug), 48 hours (metabolite)
- Opioids: 1 to 4 days (varies by type)
- Methadone: 3 to 14 days
- Short-acting benzodiazepines: 3 to 5 days
- Long-acting benzodiazepines: up to 30 days
These ranges assume average metabolism in a healthy adult. Older age, liver or kidney problems, chronic heavy use, and drug interactions can all push the upper end higher.