1. Drug Detection Times

Drug tests detect drugs as well as metabolites. Metabolites are the byproducts of a substance after it has run through your system. To determine whether you will pass or not, it is important to know how much of the illicit metabolites are in your urine, and how much is tested for. Table 1.2 will give you an approximation, however, it varies depending on a number of factors. Testing method and levels tested for are major factors.

1.1 Half-Life of Tetrahydracannabinol (THC)

The half-life of THC concentration ranges between 0.8 to 9.8 days. There is too much human variation to even approximate how long THC will be detected in the urine of an individual. Infrequent users with a fast metabolism will have the shortest detection time. Frequent users with a slow metabolism will have the longest detection time. The only way to estimate a detection time is to consider the lower and upper bounds—3-30 days—and decide based on the factors mentioned.

1.2 Detection Times of Several Drugs

Drug Approximate Detection Time
Amphetamines 2-4 days
  Short-Acting (Secobarbital) 1 day
  Long-Acting (Phenobarbital) 2-3 weeks
Benzodiazepines 3-7 days
Cannabinoids 3-30 days
Clenbuterol [PE]  2-4 days [F1]*
Cocaine 2-4 days
Codeine 2-5 days
Euphorics (MDMA, Psilocybin) 1-3 days [F2]*
LSD 1-4 days [F6]*
Methadone 3-5 days
Methaqualone 14 days
Nicotine Unknown [F5]*
Opiates 2-4 days
Peptide Hormones [PE]* Undetectable
Phencyclidine (PCP) 2-4 days [F4]*
Phenobarbital 10-20 days
Propoxyphene 6 hours to 2 days
Steroids (Anabolic) [PE]*
  Oral 14 days [F3]*
  Parenterally 1 month [F3]*

Detection times vary depending on analytical method used, drug metabolism, tolerance, patient's condition, fluid intake and method and frequency of ingestion. These are general guidelines only. Try to call in sick on test day to delay one more day if possible.

Other factors determining degree of intoxication include metabolism, tolerance, frequency of intake, fluid intake, amount of marijuana, potency of marijuana, and length of time you've been a user.

If you use marijuana on rare occasions, your urine may be clean of metabolites in less than a week. There is a common and strange phenomena that occurs with chronic users. You would expect a chronic user to have the longest detection time and the smallest chance of passing. This is not always the case. A chronic user with a high tolerance will eliminate drugs quicker than an occasional user. Chronic users have tested negative after a week long binge.

Lipid tissue also makes a huge difference. Skinny users not only have a faster metabolism, but also lack storage for THC metabolites. Fat will cause a lag in excretion pattern, and lead to a longer detection time. You should now be able to understand why an individual's detection time for THC is so unpredictable.

There is an inaccurate program that will plot a graph of time versus percentage of THC in your system given the days you've smoked. The program is called Marijuana Test and you can download it here. Marijuana Test cannot possibly be accurate because it doesn't have any way of measuring the potency of the weed, and it leaves metabolism out of the equation.

1.3 Definition of a Positive

50 nanograms of THC metabolites per milliliter defines a "presumptive positive" by NIDA certified labs. This value was originally 20 ng/mL, but too many false positives resulted. So the level was raised to 100 ng/mL to reduce false positives. As of January 1995, the threshold was lowered back down to 50 ng/mL because drinking water would easily bring a positive below 100 ng/mL. Be aware that these cutoffs are not universally consistent. Following is a table for cutoffs of other drugs:

Drug Screening Cutoff GC/MS Cutoff
Amphetamines Class 500 500
Amphetamine 500
Methamphetamine 200
Barbituates 200 100
Cocaine 150 150
Marijuana 50 15
Opiates 300
Codeine 300
Morphine 300
Phenyclidine 25 25
All cutoff levels are in micrograms/mL

1.3.1 Passive smoke and positives

Is it possible for secondhand marijuana smoke in a car to cause you to fail the next day? It is possible that secondhand marijuana smoke will raise someone to the 50 ng/mL level, however, extreme exposure is required.

For instance, a closed car full of marijuana smokers and a non-smoker may render the non-smoker positive for both urinalysis and the hair test, provided that they are sealed in the car for a while. The United States army did a case study where volunteers were put in a room pumped full of smoke for an hour, five time daily. Subjects started testing positive after the second day. The non-smoker would have to take in virtually as much second hand smoke as a smoker. Non-smokers are safe in a ventilated area, as long as they don't get a hair test.

According to one source, simply blowing crack smoke on ones hair may cause a positive hair test. Second hand pot smoke doesn't affect the hair test results as much as crack smoke does, mainly because exhaled smoke contains no THC.

A study done by a group of doctors in Canada at Dalhousie University, concluded that more than 90% of the THC is absorbed into the lungs within the first seconds of inhalation. Another study confirms this, but they put their number at 95% absorption. The 5-15% of THC that isn't absorbed is due to THC loss in trace smoke, or smoke that never enters the lungs.

1.4 Decreasing Detection Times

Increasing metabolism is probably the most effective way to decrease the time period that drugs can be detected in your system. Physical activity can increase your metabolic rate as much as two thousand percent! Nothing beats proper training taken to an extreme. A high calorie diet is the next best way to increase metabolism. Consuming mass quantities of high calorie food will increase metabolic rate by up to 10 percent. On the contrary, a malnutritious, or light, diet could lower your metabolism by 10 percent. So exercise with intensity, and eat big.