How Long Do Drugs Stay In Your System?
Many factors play into how long drugs stay in the system of an individual. These factors can include weight, body mass, drug tolerance, physical activity, and more. Drugs – such as cannabis, heroin, cocaine, and alcohol – can last within the body of an individual for days, hours, weeks, or longer.
After drugs enter the body’s metabolism, they must be processed before they can be expelled to the fullest extent. This means that they may still be detectable for some given amount of time after being consumed.
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Due to the fact that drugs remain within an individual’s body for an extended time period, this allows for a wide range of available testing methods that use various means to indicate the presence of a given substance in a subject.
Largely, drugs are eliminated by the kidneys and liver through urine and natural processes.  While in the body, drugs are stored in tissue that can include hair, teeth, bone, or fat cells.
What does the ‘half-life’ of a drug mean?
A phrase that references the time it takes for a given drug to reduce its blood concentration by half of its original value, “half-life” is a term used to provide an estimate of the duration within the human body that a drug will exist. 
This is used only as an approximate guide and varies depending on circumstances, the substance, and the individual in question. Borrowed from other areas of study, it generally takes 5.5 half-lives for a drug to completely leave an individual’s bodily system.
How long do drugs stay in the system – per hour?
The time that a given substance remains within the body depends greatly upon the drug in question. For example, heroin spends a relatively brief amount of time in one’s system when compared with other drugs such as marijuana or methadone.
Another primary factor that comes into play is how much of the drug was used and for how long. If only a small amount of the drug was used, the body may fully process the amount in as little as just a few days, whereas the effects of a heavy amount could last for weeks.
How long do different drugs stay in the system?
Below we have listed some of the most commonly abused drugs and the period they stay in your system: 
- When consuming alcohol, a general rule is that alcohol will remain in your system for 1 to 12 hours, or rather, once your blood alcohol concentration reaches .015% it takes approximately one hour to leave the body
- For 1-3 days prior to ingesting amphetamines, the presence of the drug can be identified within a urine sample, and can also be picked up through saliva tests, hair tests, and blood tests
- Long-acting barbiturates may be discovered in a person’s system for up to 140 hours, and in the case of short-acting barbiturates, the time is lessened to 40 hours
- When it comes to benzodiazepines, it will depend on many variables such as dosage, the potency of the drug, and how frequently it was used. Generally, the time-frame for testing benzodiazepines is between two to five days, but possibly up to seven days after heavy usage
- A class A stimulant, cocaine has a shorter time frame in which it can be found within the body – 3 days after heavy use, and up to 2 weeks for regular and habitual users
- Heroin ranks high on the list of substances that are most rapidly dissolved from the body – as quickly as eight minutes, in fact
- Referred to as “T.H.C”, users of cannabis can be tested for in several different ways, and can be recognised with testing methods for an extended period of time after having been used. For example, urine tests may display the presence of THC for anywhere up to 30 days, depending upon how regularly it has been used
- Meth by-products present within the body peak at about12 hours, and can be detected within urine from 2 to 4 days after having been used
- Extremely powerful painkillers, oxycontin lasts within a person’s system up to 4 days after use
- Saliva tests can detect the presence of GHB up to 6 hours after use, while urine tests can detect it up to 12 hours. Blood tests can detect it after 8 hours, while the less reliable hair strand test can test for GHB up to one full month later
- Having a high potential for misuse, methadone can be tested within urine for up to seven to nine days after taking it
- Codeine can be tested for up to two days through urine tests, one day after use from saliva tests, for up to 24 hours after use from blood tests, and up to 10 weeks from last consumption of the drug through hair strand tests
- Using a urine test, MDMA can be detected for up to three to four days, up to 10 hours after use using a saliva test, and up to four days using a blood test
- Ketamine may be tested for 3-5 days after using it with a urine test, for 24 hours with a saliva test, and up to 2 weeks using a blood test
Why is drug testing important?
Drug testing helps many organisations from schools and workplace establishments to determine whether their members are sober and qualified to engage in day-to-day activities, or help agencies and companies perform duties and make important decisions. Using drug tests, these entities can identify problems or threats and intervene when necessary.
Finding drugs in the system of employees can result in disciplinary action, termination of employment, and even legal repercussions. Furthermore, testing for drugs in the system of people who have recently left prison is crucial to them sticking to their parole. Drug testing is a means of keeping people who would otherwise pose a threat to themselves or society on the right path. 
How do authorities test for drugs in the system?
Drug testing methods come in many different variations, but can range from breath and sweat testing to urine, saliva, blood, and hair. Hair testing usually provides the longest window of availability for whether or not a drug is still within a person’s system, while urine testing is one of the most well-researched and commonly used methods.
While the other methods can be applied across the board for a wide variety of substances, breath testing can only be administered in the cases of alcohol use.
Understanding how the body varies drug absorption
We must understand that so many factors come into play regarding how an individual metabolises a substance within the body, that it’s nearly impossible to know for certain how long it will be able to be tested for.
However, general windows of testability can be applied to individual testing methodologies and practices for giving us a basic approximation. Factors such as hydration, body mass, and frequency of use are all strong considerations that come into play.
What you need to know about urine drug testing
Urine samples are the most common form of drug testing within the workplace, and can detect a wide number of commonly used substances while also being available in an array of testing formats.
These include 6-panel, 10-panel, and 16-panel options that screen and test for a wide number of drugs. While it is commonly believed that drinking excessive water is one way to pass the test dishonestly, in fact, this will only lead to an indecisive result.
Possible consequences of drugs in the system
Consequences of a positive test result vary for different situations but could lead to a dismissal from a work position, legal penalties during an arrest, or negative consequences if the person is enrolled in a government programme.
It always helps to be as clear as possible between parties about the ramifications of both a positive and negative test result so that each person can be up-front and know what to expect following the outcome. 
How far can a drug test look back?
The kidneys play an essential role in determining exactly how long a drug will remain within the bodily system of an individual, and if dehydrated, may lead to a longer period of time where testing can occur.
Of course, many other factors such as how the drug was taken, how long ago it was taken, and how much of it was consumed all play vital roles in determining whether or not it can still be tested for using different techniques.
Using the testing kit exactly as the given instructions describe and consulting closely with a trained and qualified professional are good ways to ensure that the test goes smoothly and according to plan.
How to overcome your fear of drug testing and overcome your addiction instead
It’s important to understand the drug tests are only intended to give an accurate picture of whether or not a drug has been used recently. They’re not meant to penalise or bring unjust harm to an individual.
By following directives and abstaining from prohibited drug and alcohol use, especially during periods where random or regular testing will occur, a person has absolutely nothing to fear when confronted with the prospect of a drug test of any kind. 
Of course, it’s always good to be mindful of any pharmaceuticals or prescriptions that you may be taking, or any other factors that could produce a false-positive result. Drug tests remind us all that sobriety is not only good practice for one’s individual health and mental well-being, but for their personal and professional life as well.
Overcome Your Fear
Worried about drug testing for yourself or a loved one? Face your addiction by calling us now on 0800 138 0722.
About the author:
Jon writes for ADT Healthcare and a number of other websites. Jon graduated with a degree in psychology in 1992. Jon has been in recovery for 19 years.