Many recommend to collect urine only from the middle of the stream in order to pass a drug test. Is it supported by science?

When it comes to drug tests for cannabis use, many people will try anything to pass. Although some techniques are complicated or expensive, there is one that is just so simple, I bet people do it whether they really believe in it or not.

This is the “midstream urine” technique. Folk knowledge says that the initial urine and last urine when you pee has the most “toxins” in it. So you should pee a little in the toilet, fill up the pee cup as much as necessary, then release the rest into the toilet.

This technique is certainly popular since almost everyone puts it in their “how to beat a drug test” guide. Let’s take a look at a few. Here is one from Jezebel:

You’ll want to give your best (cleanest) sample of urine…time of stream plays into your success with this. When you’re actually conducting catch your urine in the cup midstream.

These guys like it so much, they put it at #1 on their guide:

If you take nothing else away from this article about how to pass a drug test, never use the last or first part of the urine stream for testing. The midstream of your urine carries fewer levels of toxins, so try to eliminate a little and then get some in that cup.

Other notable fans of midstream urine include Maxim Magazine and A-Rod (although he used it for steroids and not cannabis).

With so many media and celebrity endorsements, surely this technique must work? While nobody has done an actual scientific study to assess collecting urine midstream, we can use our scientific knowledge to see whether this one is even feasible.

THC Metabolites and Your Urine

After consuming cannabis, your body converts the THC through several steps to a metabolite called THC-COO-glucuronide. For the sake of this article, the glucuronide metabolite is the only one that matters. It is the only one that is excreted into the urine in high levels and it is the one that is primarily detected in urine drug tests.

For more details, here are complete explanations of THC metabolism and urine drug testing.

THC-COO-glucuronide is cleared from your blood by your kidneys. The kidneys create urine (containing the THC-COO-glucuronide) which travels through the ureters to the bladder. Your urine is stored in your bladder until you pee, at which point it exits through your urethra.

Now this part is super important (especially if you weren’t a chemistry major) – the glucuronide metabolite is in solution in the urine. Solutions have some very specific properties. One of them is that the concentration is the same in all parts of the solution. Therefore, the urine at the bottom of your bladder (which will come out first) has the exact same THC metabolite concentration as the urine at the top of your bladder (which will come out last).

Is There Any Possible Way  That Midstream Urine Could Beat a Cannabis Drug Test?

Based on what I wrote above, there is a 99.9% chance that the midstream urine technique is a total myth. However, I’ll entertain some remote possibilities, just to be sure.

There are only two possible reasons that collecting urine midstream could matter:

• THC-COO-glucuronide is precipitating out of solution in your bladder
• Residual THC-COO-glucuronide is remaining in your urethra from a previous pee

On the face of it, neither is very likely, but let’s take a look:

1. THC Metabolite Precipitation in Urine

Every molecule has a limit to its water solubility. Imagine when you add too much sugar to coffee or another beverage – some of it just settles to the bottom.

As explained above, the THC-COO-glucuronide metabolite is the primary metabolite excreted into urine and detected in cannabis drug tests. If this metabolite reached its limit of solubility in urine, then it would be possible for it to precipitate out of solution (meaning that there would be solid crystals of this THC metabolite that could settle to the bottom of your bladder). When you pee in the cup, these THC metabolite crystals could come out first in the initial urine. After processing of your urine to prep for the drug test, the THC-COO-glucuronide could go back into solution, contributing to a positive test result.

Why it can’t be true: The highest urine concentration of THC-COO-glucuronide that I have ever read about was 3.4 uM (typical concentrations even for regular cannabis users are lower – this is an extreme).  The predicted aqueous solubility (using this solubility predictor tool) of THC-COO-glucuronide is 340 uM. Urine THC-COO-glucuronide concentrations are 100 times lower than the solubility limit, even in cases of extremely heavy cannabis use. There is no way that this THC metabolite will precipitate out of solution and so this cannot be responsible for midstream urine containing less THC metabolites than the initial urine.

2. Residual THC Metabolite in Urethra

Let’s say you urinate once prior to your drug test. Some residual urine will remain in your urethra. The next time you urinate is to take the drug test. Your urine from the second pee could pick up the left over THC metabolite from your first pee, boosting the THC metabolite concentration in your urine.

Why it can’t be true: Even if there is residual urine in your urethra, it’s not like the water from the urine will all be reabsorbed, leaving pure THC-COO-glucuronide crystals sitting there to be added to your next pee. You will not just be adding THC-COO-glucuronide, but also additional urine volume. Since the THC-COO-glucuronide concentration will not vary that much from one pee to the next, the residual urine from your prior pee will not change the concentration of your next pee.

Let’s even say that the water from the residual urine in your urethra is magically reabsorbed, leaving pure THC-COO-glucuronide in your urethra. The residual urine volume your urethra can hold is very small – about 1.2 mL of urine. When they perform a drug test, they will require a minimum of 30 mL of urine. This means that the residual urine from the previous pee could only add a whole 4% more THC-COO-glucuronide.

Midstream Urine – Another Drug Testing Myth

There have been no scientific studies of using midstream urine to beat cannabis drug tests. However, our analysis shows that there is no possible mechanism for the midstream urine technique to work. So it doesn’t matter whether you pee into the drug testing cup using the beginning, middle, or end of your urine. However, since there is no cost to using midstream urine, go for it if it makes you feel better.

Where did this myth come from? Who knows. Urine collection to diagnose a urinary tract infection does involve collecting mid-stream urine. The reason for this is to avoid contaminating the sample with microbes that are on the skin. I can only guess that somehow this is the basis for this drug testing myth.

[Featured image: Flickr/ dirtyboxface]