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Blood Drug Testing – How Long Do Drugs Stay in Your Blood?

Dr. Gerardo Sison

Medically reviewed by

Dr. Gerardo Sison

March 29, 2019

Blood drug tests are used to detect drugs in an individual’s system when other tests are no longer an option. Drugs can typically be detected in the blood minutes after it is administered until three days after.

A blood test is usually administered when other types of drug tests are not an option, for any reason. Blood drug tests have a much smaller window of detection, starting minutes after ingestion and lasting about one to three days for most substances. However, the results of blood drug tests, like other blood tests, can be influenced by a number of factors.

Blood drug tests differ significantly from other drug tests in another way because they actually test for the parent drug (the drug ingested). Because many drugs are absorbed into the bloodstream almost immediately they can be detected very easily, within the time frame they remain in the blood.

Reasons For Blood Drug Testing

While blood testing is considered one of the most accurate and invasive types of drug testing, it is also less likely to be tampered with because blood has to be drawn by a medical professional. This means the sample generally isn’t left alone with any one person for any length of time.

There are important reasons to use a blood drug test with some people. For some, there may be a history of sample tampering. Or, the results of the blood drug test could be used in criminal cases or determining employment status.

Blood drug testing is usually reserved for situations where a person is suspected of being under the influence of a substance at that moment. These situations typically are work-related, ordered by an insurance company, or in an emergency room setting for toxicology purposes.

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Advantages Of Blood Drug Tests

Although blood drug testing is not common or considered the gold standard of drug testing, there are two solid advantages for using blood drug testing.

The first is that there is more flexibility to blood drug testing because they can order additional tests that look for specific substances if needed. The other key advantage to a blood drug test is there does not appear to be any known tricks to help pass a blood drug test.

Disadvantages Of Blood Drug Tests

The big disadvantage of blood drug tests is that they are quite expensive, in addition to the fact that there is a limited detection window. A person has to be trained in order to collect the specimen (phlebotomists), and the collection method is the most intrusive of all drug testing.

There is an increased risk of infection with blood drug tests because, in order to collect the sample, the vein must be punctured. However, these disadvantages do not outweigh the benefit of being able to detect recent drug use using an established method in a laboratory setting.

Factors That Can Affect Blood Test Results

There are many variables that can affect the outcome of a blood drug test. The following are a few of the more common reasons:

  • age
  • how often the drug is used
  • dependence on drug
  • body mass
  • amount of physical activity

All of these factors will affect how long the substance stays in your blood. The majority of substances are detectable in the blood for no more than one or two days under normal circumstances. This time frame can increase if a person is heavily abusing drugs, or struggling with a substance use disorder (commonly referred to as substance abuse or addiction).

When a person is older or doesn’t have a lot of physical activity, their body may take longer to break down substances. This can lead to drugs being at detectable levels in the body for longer periods of time. Additionally, the more body mass an individual has, the longer it takes for the substance to be broken down by the body.

Drugs That Blood Testing Can Detect And Timelines For Each

A blood drug test can test for many parent drugs, including alcohol, and specific tests can be ordered in addition to the standard. These drugs are detectable for only a certain amount of time before they are broken down and expelled in the urine.


When testing for alcohol in the blood, the chemical that is tested for is Ethyl alcohol, and this is usually present for about 12 hours after the last consumption.


Stimulants, like amphetamines, can be detected in the blood an average of 12 hours after the last use. These types of drugs are often referred to as speed or black beauties. Long-term use may affect detection rates in drug tests.


Methamphetamine is also a stimulant, and has effects similar to cocaine but lasts a little longer. Meth tends to be detectable in the bloodstream for about 24 to 72 hours after the last dose is ingested.


Barbiturates were historically prescribed for anxiety and insomnia, and have varying degrees of detectability. Longer-acting barbiturates, like phenobarbital (Luminal), are detectable for longer periods of time. The average time of detection ranges from one to two days in the blood.


The type of benzodiazepine taken can affect detection in the blood. Some benzos, like alprazolam (Xanax) or clonazepam (Klonopin), may not show up on the test, depending on additional factors. On average, benzodiazepines can be detected in a blood drug test ranging from six to 48 hours.


The active ingredient in marijuana, referred to as cannabis, is detectable in a blood drug test for an average of six to 24 hours. Long-term, frequent, or heavy marijuana use can result in a positive test for cannabis for an average of seven days using a blood drug test.


Cocaine is a stimulant that stays in your system the longer you continue to use it. Long-term use leads to an accumulation of cocaine in the tissue of the body. As a result, the detection time is much longer. For someone who casually uses cocaine, the detection time is much shorter. On average, cocaine is detectable in a blood drug test for approximately 12 to 48 hours.


Opioids are drugs that are derived naturally from the poppy plant or created synthetically to mimic the effects of natural opioids. They vary in detection time, and some of the more common opioids and their detection times in the blood after the last dose are listed below.

  • codeine: within 24 hours
  • heroin: up to six hours
  • morphine: within the first twelve hours
  • methadone: 24 to 36 hours

LSD (lysergic acid diethylamide)

Typically referred to as “acid”, LSD is largely undetectable due to the small amount of the drug in the body and a very limited window of detection in a blood drug test (0 to 3 hours). However, there is a specific test that can be ordered that screens blood, urine, and stomach contents, and also screens for the metabolites for LSD.

PCP (1-phenylcyclohexylpiperidine hydrochloride)

PCP is a hallucinogen typically detectable in blood tests ranging from 12 to 24 hours. This specific substance’s detection window is affected by additional variables, ranging from age and body mass to health conditions and hydration levels. It is difficult to determine exactly how long PCP will be detected in any one person.

Taking A Blood Drug Test

If you have to take a blood drug test, make sure you take with you a list of all medications that you take, both over-the-counter and prescriptions. Include supplements and vitamins as well. Show up on time, and be ready to answer any questions they may have.

If taking a blood drug test is problematic because a positive result could have a significant negative effect on your life, or if you think that you have been misusing or abusing a substance to the point of an addiction or substance use disorder, please reach out to us today.

U.S. National Library of Medicine: Medline Plus - Drug Testing

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