Can Taking Aspirin Help You Pass a Marijuana (THC) Drug Test?

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Aspirin has for long been touted as a remedy for passing a test. There are two sides to this. The good news is that it actually works.

There are several scientific pieces of research that prove that taking aspirin before a test may interfere with the immunoassay signal thereby leading to a false negative for THC. On the other hand, you are not always guaranteed to beat the test. It’s a fifty-fifty situation.

All in all, this article will explain how to pass a urine drug test using aspirin and scientific evidence.

How to use aspirin to pass a urine drug test

The internet community has two methods of doing this;

Method 1

Method 2

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How does aspirin work to help cheat a urine test?

There lacks concrete evidence of how aspirin helps in creating a false negative so far. However, forum buddies who’ve used this method successfully have all sorts of explanations.

The most general suggestion is that aspirin masks the drug metabolites in urine thereby making them undetectable in tests.

Another suggestion is based on salicylic acid – the active ingredient in aspirin. This school of thought claims that when aspirin is ingested, the salicylic acid is absorbed into the bloodstream where it burns off the THC metabolites floating in the blood.

This minimizes the amount that is released into the urine and which is later diluted below the cut off level through dilution.

Still, others believe that aspirin directly affects the testing equipment thereby faulting its performance. This leads to a forced negative.

Whichever claim is true, several research studies show that aspirin can help you skirt the test and skew the results to your favor.

Scientific Evidence

A 1994 research study published on National Institutes of Health wanted to investigate whether ingesting aspirin decreases signal in EMIT assays during a urine test for benzoylecgonine (metabolites released into the urine after ingestion of cocaine).

The researchers were driven to carry out this study after realizing that most of the urine samples that were sent to their labs for analysis around that time had abnormally lower rates of changes in absorbance.

For clarity purposes, the absorption rate in urinalysis is used to determine the number of drugs absorbed into the body specifically at the site of absorption. However, since it’s almost impossible to access the receptor sites where drugs are absorbed inside the body, researchers measure the concentration of the drug metabolites in body fluids including urine and blood plasma.

In the Emit d.a.u method, the absorption rate is done by first determining a cutoff concentration (also known as a low calibrator). During the test, if the observed signal goes beyond the cutoff signal, the urine sample is considered positive for the drugs tested. On the other hand, if the signal is lower than the cutoff, then it is considered negative for the drugs being tested.

cuttoff levels

So, as I have mentioned, these researchers had observed that several urine samples reproduced a negative bias. Upon further experiments, they realized that most of these samples had salicylate (components of aspirin) concentrations.

Thus, they wanted to determine whether the salicylate components were responsible for the negative bias.

To do this, the study involved 6 subjects (5 males and 1 female) with a history of taking cocaine. They were required to collect one urine sample each before ingesting 4 x 325mg aspirin tablets and then a sample after every 2 hours up to 20 hours.

40 urine specimens were taken for analysis, and the results were plotted on a graph. According to the results, 20 of the samples showed a negative absorbance rate <-4mA/min. On the contrary, results from 100 subjects who didn’t take cocaine or salicylates had an absorbance rate <-1.05mA/min except 2 who had <-4Ma/min.

Proving that the salicylate compounds caused the negative bias

The researchers went ahead and wanted to determine whether the salicylate compounds were responsible for the negative bias.

To do this, 6 other drug-free subjects ingested 4 x 325 mg aspirin pills and collected urine samples at intervals of 2 hours. The results were plotted in a graph of delta absorption rate against time.

It was observed that the maximum salicylate concentration corresponded directly to the maximum negative absorption rate.

This is a clear indication the salicylate compounds might have caused the negative bias in the other tests.

Negative biases observed for other Emit d.a.u. assays after salicylate ingestion lead us to conclude that ingestion of therapeutic doses of aspirin may cause false-negative results for drug screens in urines by this technology.Department of Pathology, University of Louisville School of Medicine, University of Louisville Hospital, KY 40292.

Will adding salicylic acid directly into the urine samples with cocaine have similar effects?

The researchers also wanted to determine whether adding aspirin directly into the urine sample would yield similar results. To do this, they added salicylic acid to urine samples from 4 individuals: 1 without benzoylecgonine (BE) and 3 with BE.

Interestingly, adding salicylic acid directly into the urine sample did not yield the same results. The researchers noted that the salicylic acid must be physiologically metabolized to produce a negative bias.

Will aspirin have similar effects when used on other EMIT assays such as THC?

To determine whether salicylic acid would have similar effects on other Emit assays, urine samples were taken from subjects who had used opiates, amphetamines, benzodiazepines, phencyclidine, barbiturates, propoxyphene, and tetrahydrocannabinol (THC).

Reduced signals were detected in each sample. Therefore, it was concluded that taking aspirin a few hours to the test may decrease the signal on these EMIT technologies.

What amount of Aspirin is enough to cause a negative bias?

According to the researchers, the subjects tolerated the four 325 mg pills of aspirin. Notably, according to the graphs, the subjects took a different time to reach the peak of the salicylate concentrations. This means that individuals require varying amounts of salicylic acid and time to reduce the signal.

The researchers also add that medical texts show that daily doses of up to 10 (325 mg) pills of aspirin are prescribed for patients suffering from rheumatoid arthritis.

Unfortunately, there isn’t a way of determining exactly how many tablets one would need to take to falsify a test.

Do People Pass Urine Tests Using Aspirin Today?

Well, scouring a few internet forums, you’ll come across lots of people who have passed the test with flying colors using this method. However, there are still others who fail miserably.

It’s over a decade since it became evident that aspirin can be used to falsify a test. Needless to mention, there have been a lot of changes in EMIT technology, and it’s now possible to detect salicylic acid in urine.

Even worse, most labs will still detect the drug metabolites regardless of the presence of aspirin ingredients in the urine or not.


Aspirin has the potential to help you beat a test. But there’s also a high risk of failing. If you are desperate for passing the test, then the best idea would be to combine this ‘magic pill’ with the dilution method.

Dilution method is the easiest and surest way to beat a urine drug test. The best part of this method is that it can be used as a same-day solution and won’t cost you much.

However, as we have indicated in another article on how to pass a urine test using water, this method has some technicalities to it and requires expertise. Among other things, you’ll want to consider your Lean Body Mass besides keeping a close eye on your urine’s Specific gravity and creatinine levels.

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Daniel Miller
Hey there! I'm Daniel. My research into cannabis shows how cannabis affects health, including how cannabinoids can be used in the treatment of various diseases.

One comment

  1. Micah says:

    Great article, thanks for the research. I’ve done a lot of reading and research, living in Northern CA, and by far some of the best stuff I’ve read. When was this posted?