Harm Reduction: Everything you wanted to know about urine drug tests screening

Drugs are eliminated from the body through sweat, urine, and feces. When a drug is consumed, it passes through the liver and undergoes a process of "destruction" in which "remains" called metabolites are generated. These metabolites are what are usually detected in drug tests.

The most common drug tests are those done on urine. Routinely, the most common forms of drugs are not detected in blood (with the exception of alcohol). Detection times in urine depend on consumption patterns, individual characteristics, and, above all, the sensitivity of the tests used. As a rough guide, the average detection times are:

Drugs like MDMA, cocaine, opioids, benzodiazepines, or amphetamines can be detected in the body 2-3 days after consumption. To be completely sure, one or two weeks would be sufficient.

Regarding cannabis, the issue is a little more complex. Cannabis is deposited in the fatty tissues of the body, and its effects can last a little longer. In a sporadic cannabis user, their metabolites can be detected between 7-10 days. In habitual users, metabolites can be detected for up to 30-45 days.

For drugs like GHB or ketamine, tests are not available in most medical services. Their determination can be made in specialized, forensic labs.

There are "urine cleansers" that supposedly accelerate the elimination of drugs or allow the result of a urine sample to be disguised. Their composition is unknown, and their effectiveness uncertain. In the laboratory, parameters (pH, nitrites, density, etc.) are usually determined to detect adulterants in urine.

The amount of drugs eliminated over time depends on factors in the body itself. Drinking a lot of fluids or dairy products, exercising, or stimulating sweating does not have a real effect on the time it takes for the body to eliminate drugs.

Through complex techniques, it is possible to detect the substances consumed by a person in their hair. These techniques are very expensive and are usually used only in judicial procedures.

In principle, routine blood or urine tests do not request the determination of toxins in urine. Nor should they be determined in the context of a work-related medical examination without the express consent of the patient. Otherwise, it could be susceptible to a complaint for violating the patient's privacy.

It is unknown whether passive exposure to marijuana smoke can result in a positive drug test. Existing studies have yielded conflicting conclusions. Although it is theoretically possible for passive smokers to test positive in poorly ventilated and highly contaminated environments, it is considered very unlikely to happen in practice.

Most tests can produce false positives (a positive result without consuming the substance). In many cases, these results are produced by the use of another drug. Opioid tests (heroin) can produce false positives after consuming morphine.

Other substances that can offer a false positive result are:
• Amphetamines: Aripiprazol, Bupropion, Ephedrine, Labetalol ,Metformine, Ranitidine
• Benzodiacepines: Sertraline, Efavirenz
• Cannabis: Non-steroideal anti inflammatoires (aspirin, ibuprofen, diclofenac...). Omeprazol and derivatives
• Opiates: Antibiotics family (quinolones): ciprofloxacin, norfloxacin, ofloxacin

Most benzodiazepine tests are designed to detect oxazepam or nordiazepam, which are common metabolites of several benzodiazepines (for example, diazepam (Valium®) and chlordiazepoxide (Tranxilium®)). However, other commonly used benzodiazepines such as lorazepam (Orfidal®) and alprazolam (Trankimazin®) have a different excretion pattern and are not detected by most immunoassay tests unless urine is subjected to prior treatment. Some benzodiacepines can be detected up to 7 days in common urine tests.

Amphetamines test detect amphetamine, methamphetamine, MDMA and their derivatives (MDA and MDEA). However, they are also the ones most frequently associated with false positive results due to the presence of other drugs and cross-reacting substances. It is difficult to develop antibodies that are specific for amphetamine and methamphetamine since the molecular structure of phenethylamine, a precursor of both compounds and other drugs of abuse, is similar.

A urban legend about drug tests in this sense claims that it is possible to test positive for amphetamines after using nasal sprays. Indeed, one of the most commonly used mentholated nasal inhalers (Vicks Nasal®) contains 5 mg per container of the levo isomer of methamphetamine (L-methamphetamine, remember Unit 1) which is not psychoactive but is a nasal vasoconstrictor. However, each administration involves the local use of much smaller amounts, and its detection in urine tests has not been demonstrated in well-designed studies.

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