Measuring how long drugs remain in your system is based on the drug's half-life, or the amount of time it takes a drug to leave your body. The half-life is best described as the amount of time it takes the liver and kidneys to filter and break down the drug within your bloodstream. Most clinicians determine that a drug has left your system after five half-lives, when less than 3% of the drug can be traced.

How Long Do Drugs Stay in Your System?

Depending on the test that is used, and the amount of drug ingested, the following table can be used as a guideline. Please note that this guideline does not take into consideration any other medical conditions you may have.

This table only lists the detection time of common drugs. For more detailed information, click here.

Common Types of Drug Tests

How long do drugs stay in your system? That depends on the kind of tests you'll go through. Below are some common tests that are used:

• Breath Test: When consuming alcohol, traces can be measured on your breath with a breath analyzer. A device called a Breathalyzer is commonly used by law enforcement to determine the amount of alcohol in your bloodstream when they suspect you have been drinking.
• Blood Test: Blood tests take longer than a Breathalyzer to process, but are very effective and accurate when screening for alcohol and drug use. Blood tests are also commonly used by law enforcement when drug or alcohol use is suspected while driving.
• Urine Test: A popular test for employers screening for alcohol and/or drug use with current or potential new hires, is a urine test. The test is fast, generally accurate, and convenient during random drug testing of employees.
• Saliva Test: The saliva test is more commonly used for DNA evidence. However, it is also sometimes used to determine drug and alcohol use when blood or urine tests not otherwise available. Drug and alcohol traces can be detected from a few hours after consumption up to a few days with drug use.
• Hair Test: Hair sampling is often the preferred method of detecting long term drug use. It is very accurate because as the hair grows a time line of drug use, along with an estimated dosage amount, can be determined over a period of months as the hair grows (about ½ inch per month).

Factors That Will Affect the Duration Time of Drugs

How long do drugs stay in your system? That's hard to predict, because drugs affect people in different ways, and the time a drug stays in your system depends on various different factors including:

1. Metabolism

The faster the metabolism rate, the faster your body will use things up, and the slower the metabolism means that drugs will take longer to dissipate. Knowing what type of metabolism you have can help you predict how long drugs will remain in your system.

2. Body Mass

People who are overweight usually find themselves with a slower metabolism rate, whereas slimmer people usually have a faster metabolism rate. However, there is no specific scientific evidence that supports the notion that a lower body mass has a better advantage of passing a drug screening than an overweight person.

3. Hydration

Some people believe that drinking lots of fluid can affect the outcome of a drug test. What they do not understand is that while lots of fluids may dilute a urine sample, most urine specimens are measured and compensated for 'dilution' of the sample. Furthermore, with the exception of alcohol, increased fluids have little effect in flushing the system of drugs using other testing methods.

4. Amount and Frequency of Drug Use

The amount and frequency of any drug use will alter the amount of time that it takes to filter out of the body. It stands to reason that using drugs on a continuous basis over a long period of time will lengthen the amount of time that detectable amount drugs can be found in your system.

5. Gender

Generally speaking, women have less water in their body than men of the same weight, and metabolize alcohol differently than men. Women will achieve a higher concentration of alcohol in the bloodstream than men who drink a similar amount of alcohol. Additionally, women also have smaller quantities of enzymes that break down drugs after consumption, thus affecting the rate and concentration of drugs or alcohol entering the body.

6. Age

The older you get, the longer it takes to process drugs and alcohol, and the very old often have limited liver and kidney function, which affect the way drugs and alcohol are metabolized. The elderly also have lower thresholds for toxicity to alcohol and drug use.

7. Genetics

Strong evidence suggests certain people and ethnic groups with genetic disorders will often influence the way alcohol and drugs are metabolized in the body. These genetic factors also are, at least in part, responsible for alcohol and drug dependency as a result.

8. Diet

Dietary supplements, which are also referred to as health supplements, include herbal products that can change enzyme levels in the liver, and foods such as grapefruit or orange juice can change enzyme levels in the stomach, thus affecting the rate of metabolism.

9. Disease

Disease that affects the liver, kidneys, brain or heart, can have an adverse effect on the way your body metabolizes drugs or alcohol.