LSD produces marathon trips, with psychedelic effects lasting all day and in rare cases, flashbacks that can turn up for years. But there’s no truth to rumors that the drug remains in your fat stores or spinal cord forever. As with other water-soluble drugs, LSD and its metabolites are rapidly cleared from your body, gone from your blood within 24 hours and from your urine within four days at the very most.
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How long does LSD take to kick in?
LSD typically takes effect in 20 to 90 minutes. Dissolving a tab or putting a drop of liquid under your tongue will lead to faster absorption and effects. If you swallow it, the psychedelic drug takes longer to reach your bloodstream, especially if you have food in your stomach.
The time of onset also depends on the dose and your body composition, age, metabolism, and liver health.
The effects of LSD usually peak two to three hours after it’s taken.
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How long does LSD last?
The effects of LSD—hallucinations, visual disturbances, sensory distortion, and euphoria—typically last between six and 12 hours.
The duration depends on the dosage. In one study, the mean duration of subjective effects was eight hours after 100 micrograms (μg) and 11 hours after 200 mg. At very high doses, the experience may extend to 20 hours.
All classic psychedelics work similarly: they have a similar structure to the neurotransmitter serotonin and bind to serotonin receptors in the brain.
But with LSD, the effects last even longer because of the unique way the drug’s molecules attach to the receptor, as revealed by X-ray crystallography. LSD molecules get wedged in the receptor’s binding site pocket and part of the receptor folds over the LSD molecule like a lid, keeping it trapped. Psychedelic effects last for hours until the molecule finally unsticks.
Afterglow and comedown
For reasons that aren’t fully understood, LSD may give you an afterglow: an elevated mood, enhanced feelings of social connection and compassion, and lower anxiety, lasting from one day to two weeks after the trip. Conversely, you may also have a comedown, with fatigue, low mood, and confusion about your experience and the insights it’s given you.
In the event of a bad trip, hallucinations may persist for up to 48 hours and psychosis for three to four days.
How long does LSD stay in your system?
LSD is quickly cleared from your body, with the liver breaking it down into inactive metabolites. Scientists have variously measured the half-life of LSD (the time it takes for the body to eliminate half) as 2.6 hours, 2.9 hours, hours, and 3.6 hours. After four to five half-lives or 10 to 18 hours, the vast majority of the LSD you took will be gone.
Some of these inactive metabolites are removed more slowly. The main metabolite, 2-Oxo-3-hydroxy-LSD (O-H-LSD), has concentrations 16 to 43 times greater than LSD and a detection window that’s possibly days. It’s the main marker of LSD use.
However, neither LSD nor these metabolites are fat-soluble, as drugs like marijuana are, so they don’t stick along very long and should be gone within four days at the most.
Can LSD stay in your system for years?
For decades, reports have circulated that LSD remains in your fat stores to return months later, producing another round of psychedelic effects. Another rumor suggests LSD stays in your spinal cord forever. These reports are nothing but urban legends. LSD and its metabolites aren’t fat-soluble at all and while animal studies have shown it does cross the blood-brain barrier and enter the cerebrospinal fluid, it doesn’t stick around.
But the myths likely emerged as an explanation for a very real phenomenon: the LSD flashback. Since LSD was first taken recreationally, people have reported that some of the effects—usually visual disturbances—resurface for weeks, months, or even years later. When these effects are constant or very distressing, they can be diagnosed as Hallucinogen Persisting Perception Disorder (HPPD).
Other psychedelics and psychoactive substances have been linked to flashbacks, but LSD is the main originator. Scientists don’t know why these conditions occur but have theorized that LSD, by agonizing serotonin receptors in the brain, damages serotonergic inhibitory neurons. This leads to long-term elevated activity in the cortex and dysfunction in the visual pathways in the thalamus, even without the presence of the LSD molecule.
Does LSD show up in drug tests?
Routine drug screening can’t detect LSD. The amounts used are too small—one-ten-thousandth of a gram—and cleared too quickly for the body. Specialized drug tests can identify LSD in its metabolites for up to four days in some people. However, these tests are expensive and will only be conducted if that’s a pressing need to confirm the presence of LSD, such as in the process of emergency medical treatment or an investigation.
Just 1% of an LSD dose is excreted unchanged into the urine. However, higher concentrations of O-H-LSD and other inactive metabolites can be identified and are detected in the urine for up to four days in some individuals.
LSD is cleared from the blood in eight to 24 hours, depending on the person. Blood tests must be done quickly to detect the presence of LSD.
Hair follicle testing can usually detect common drugs for up to 90 days after use. In three cases in medical literature, LSD has been identified in human hair. However, hair testing is not routinely done and it’s unknown how long the molecule remains in the hair. 
Factors that affect how long LSD is in your system
The length of time LSD stays in the body and the detection windows for standard drug tests vary widely, influenced by several factors:
dose: the more you take, the longer it remains in your body.
your metabolism: the faster your metabolism, the faster LSD will be broken down and leave your body.
your age: metabolism and drug clearance slow as you age
- your liver function: impaired liver function, either as a result of a medical condition or medication, can slow the metabolism of LSD.
Can you flush LSD out of your system quickly?
LSD is already eliminated from your body quickly and there’s little you can do to speed up the process. Staying hydrated and urinating regularly may slightly expedite excretion but only slightly.
You shouldn’t drink unsafe amounts of water or use any other substance to try to flush LSD or other recreational drugs out of your body. Doing so risks your health.
What to do if you’re having a bad trip
Bad trips can be anxiety-inducing, even terrifying, especially given the length of LSD’s effects. Even if you’ve taken LSD before, a bad trip can take you by surprise.
The drug’s effects, positive or negative, are caused by the molecule binding your brain’s serotonin receptors and getting stuck there for hours. There's no way to peel it off more quickly or reverse the effects.
You’ll have to ride out the acid trip. But you can take steps to make it as tolerable as possible.
Remember it’s not real. Whatever you’re perceiving is a result of the drug and can’t harm you.
Avoid too much stimulation. Get away from anything that will further overload your senses, such as loud music, lights, and crowds. Find a quiet, comfortable place to rest.
Keep yourself safe. Stay away from hazards such as heights and bodies of water.
Find a sober friend to supervise you. You should always trip in the presence of a sober ‘sitter’ who can watch over you and intervene if you begin acting irrationally or hazardously.
Stay hydrated and try to eat something. LSD trips can be lengthy so ensure you’re meeting your body’s basic needs. Although you might not have an appetite, you should try to eat something soft and easy to digest. Low blood sugar could be contributing to your anxiety.
Don’t attempt to self-medicate. Some people try taking a sedative or drinking alcohol to calm themselves during a bad trip. But adding another substance can increase your disorientation and feelings of being out of control.
Seek medical attention if you feel unsafe. If you’re physically ill, are experiencing mental health symptoms, or worry you might harm yourself, seek emergency attention from medical professionals.
- Remember it will end. Despite LSD trips lasting a long time, they do eventually end and whatever negative reactions you are experiencing will end with them.