LSD (acid) stays detectable in your blood for roughly 8 to 16 hours after you take it. The drug has a half-life of about 4 hours, meaning half of it clears your system in that time. At a typical dose, most blood tests won’t pick it up after 8 hours, but higher doses (around 200 micrograms) have been detected up to 16 hours later under controlled research conditions.
How LSD Clears Your Blood
Your liver does the heavy lifting. LSD is broken down primarily by a family of liver enzymes, with two specific enzymes playing the largest roles in the initial steps. The drug is converted into several byproducts, the most important being a metabolite that circulates at concentrations 16 to 43 times higher than LSD itself. This metabolite sticks around longer and is often used as the real marker of LSD use in forensic and clinical testing, since LSD itself disappears from blood relatively quickly.
With a 4-hour half-life, here’s roughly how the math works: if you start with a given amount of LSD in your blood, half is gone by hour 4, three-quarters by hour 8, and so on. By 12 to 16 hours, the remaining concentration is extremely small. For most practical purposes, LSD is undetectable in blood within a day.
What Affects How Fast You Metabolize It
Your genetics matter more than most other factors. People who carry certain variations in the CYP2D6 gene (one of the liver enzymes involved) process LSD much more slowly. In one study, participants with no functional copies of this gene had roughly 75% higher overall exposure to LSD compared to normal metabolizers. That translates to both stronger effects and a longer window where the drug is present in blood. Medications that inhibit the same enzyme could theoretically do the same thing.
Food also plays a role. How much you’ve eaten, the acidity of your stomach, and how quickly your stomach empties all influence how fast LSD gets absorbed in the first place, which shifts the timeline slightly. Interestingly, sex does not appear to make a difference. Studies in healthy volunteers found no meaningful pharmacokinetic differences between male and female participants.
Blood Tests vs. Other Detection Methods
Blood has the shortest detection window of any sample type for LSD. The drug and its metabolites persist longer in urine and hair. Urine testing can pick up LSD’s primary metabolite for up to 2 to 4 days in some cases, largely because that metabolite is present at much higher concentrations than LSD itself. Hair testing has the longest window, potentially months, though it is rarely used for LSD specifically.
The sensitivity of the test also matters. Modern forensic labs use liquid chromatography paired with tandem mass spectrometry, which can detect LSD at concentrations as low as 0.01 micrograms per kilogram of blood. That’s an extraordinarily small amount. Older or less sophisticated testing methods have higher thresholds, meaning they stop detecting LSD sooner even if trace amounts remain.
LSD Is Not on Standard Drug Panels
If you’re wondering about workplace drug testing, standard panels do not screen for LSD. The federal five-panel test mandated by SAMHSA covers amphetamines (including MDMA), cocaine, marijuana, opioids, and PCP. Extended panels that test for 10 or 12 substances still typically don’t include LSD. Testing for it requires a specialized assay ordered on a case-by-case basis, which is uncommon outside of forensic investigations or specific clinical scenarios.
Even when LSD-specific testing is ordered, the narrow blood detection window of 8 to 16 hours makes it one of the harder drugs to catch. The combination of tiny active doses (measured in millionths of a gram), rapid metabolism, and the need for specialized equipment means that blood testing for LSD is both expensive and time-sensitive.
How the Timeline Compares to Effects
One thing that catches people off guard is that LSD’s subjective effects can last longer than the drug remains easily detectable in blood. A typical acid trip lasts 8 to 12 hours, and residual effects like difficulty sleeping or mild mood shifts can stretch beyond that. By the time you feel fully back to baseline, LSD is likely already below detectable levels in your blood. The lingering effects are driven partly by how the drug interacts with receptors in the brain, where it binds tightly and continues to exert influence even as blood concentrations drop.