Cocaine, BZE and Blood-Sample Evidence
- Patrick Horan
- 1 day ago
- 8 min read
Can cocaine turn into BZE after your blood is taken?
YES. |
Cocaine can begin to break down after a blood sample has been taken. Some of it may turn into benzoylecgonine, usually shortened to BZE.
But that is only the beginning of the answer.
Let’s dispel one myth right away: the temperature and the length of time the blood is stored do not scientifically cause the sample to corrode.
But this is not to say that cocaine in blood cannot break down.
Facts
The fact that cocaine can break down inside a blood bottle does not prove that an MBRS result is wrong.
But the two figures on an MBRS certificate should not automatically be treated as a perfect picture of what was in the person’s blood when the sample was first taken.
There is also an important legal point.
Section 20(3) of the Road Traffic Act 2010 says that an MBRS certificate is “sufficient evidence” of the facts stated in it until the contrary is shown. It is also sufficient evidence that the MBRS followed the legal requirements that apply to it.1
In plain English, that means the prosecution can normally rely on the certificate unless evidence is produced which shows that something may be wrong.
It does not mean that every laboratory test is incapable of error. But it does mean that a certificate cannot be dismissed simply because cocaine is known to be unstable.
A proper challenge needs evidence.
Which means that in order to challenge the result from the Bureau, you will need to call evidence from a pharmacological and toxicology expert.
Good luck with that: such people, even if you could find them, will not risk their professional reputation trying to overturn an analysis of blood from the State laboratory.
This is because the science behind the testing of blood has been well documented worldwide for over 80 years.
Why are there two figures on the certificate?
A driver may open an MBRS certificate and see two separate results:
· cocaine; and
· benzoylecgonine, or BZE.
One figure may be quite low. The other may be much higher.
The natural question is:
Were these the exact figures when the blood left my arm?
The answer is not always simple.
Irish law sets separate blood limits for cocaine and BZE:
Cocaine: 10 ng/ml of whole blood
BZE: 50 ng/ml of whole blood
“Ng/ml” means nanograms per millilitre. A nanogram is an extremely small amount.
Cocaine and BZE are treated as two separate drugs for the purpose of the legal limits. A person may be over the limit for one but not the other.1
What exactly is BZE?
BZE is a substance produced when cocaine breaks down.
Some of that breakdown happens inside the body. But laboratory research shows that cocaine may also continue to break down after the blood has been taken. Depending on the conditions, that process can produce BZE and other breakdown substances.2
Scientists sometimes call this process “hydrolysis”.
In plain English, hydrolysis means that a chemical reacts with water and begins to change or break apart.
Blood naturally contains water. So the chemical make-up of a blood sample may continue to change after the sample leaves the person’s body.
That does not mean that all the cocaine will turn into BZE. It means that the amounts measured later may be affected by what happened to the sample after it was taken.
Can the blood sample really change?
YES. |
Once blood leaves the body, its chemical contents are not frozen in time.
If cocaine breaks down, the amount of cocaine measured later may be lower than it was when the blood was taken.
The amount of a breakdown substance may also change.
Research has found that the speed of this change can be affected by:
· the temperature;
· the acidity of the blood, known as its pH;
· the preservative placed in the bottle;
· the amount of preservative used; and
· how long the sample is stored.2
One study examined blood samples from 147 real cases. It found important differences between samples collected in bottles containing fluoride and oxalate and samples collected without those stabilising substances.3
Another experiment found that grey-top blood tubes containing sodium fluoride greatly reduced cocaine breakdown during collection, transport and short-term storage.4
So the words “cocaine is unstable” do not answer the question.
The real question is:
What happened to this particular blood sample, in this particular bottle, during this particular period of time?
The white powder in the Bureau blood bottle matters
The MBRS says that its blood-sample bottles contain sodium fluoride and potassium oxalate.5
Those names sound complicated. Their jobs are easier to understand.
Sodium fluoride is a preservative.
It helps to slow down changes inside the blood sample.
Potassium oxalate is an anticoagulant.
That means it helps to stop the blood from clotting.
Research has shown that sodium fluoride can slow down the breakdown of cocaine.
Temperature and storage conditions may still matter, however.2
The MBRS also reports that its laboratory operates a quality system and holds ISO/IEC 17025 accreditation.6
This is an international laboratory standard. It concerns whether a laboratory is able to carry out particular tests properly and consistently.
The Bureau obviously can.
What happens when blood is stored for a long time?
One study examined drugs in blood that had been stored for five years in tubes containing sodium fluoride and potassium oxalate.
The researchers concluded that cocaine and BZE did not remain stable over that very long period when the blood was kept at room temperature.7
That does not mean that the same level of change happens in an ordinary Irish drug-driving case.
Five years is a very long time. The result of that study should not be applied to an Irish case without first knowing:
· when the blood was taken;
· when it arrived at the MBRS;
· how it was transported;
· how it was stored;
· the temperature at which it was stored; and
· when it was tested.
Besides, blood samples taken by Gardai are analysed by the Bureau for drugs within 8-10 weeks on average. In other words, the results are known in weeks, not years, as in the study above.
What can the figures on the certificate tell us?
The figures tell us what the MBRS measured in the sample it tested.
The certificate can show:
· whether cocaine was detected;
· whether BZE was detected;
· whether that amount measured was above or below the legal limit.1
That is valuable evidence.
But those figures cannot, on their own, recreate everything that happened before the blood was tested.
The scientific studies do not provide a simple formula that allows someone to take a BZE result and work backwards to an exact amount of cocaine taken or an exact time when it was used.2, 3, 8
Too many things may affect the answer.
These include what happened inside the person’s body and what happened to the blood after it was taken.
Does a high BZE result prove that the blood changed inside the bottle?
No.
A high BZE result does not, by itself, prove that cocaine broke down after the blood was taken.
BZE may already have been present in the person’s blood. The person’s body begins breaking down cocaine after it is taken.
The scientific point is more specific.
A later laboratory result may not always provide a perfect record of the exact amounts that were present when the blood first entered the bottle.
Unfortunately, if BZE is found in your blood above the legal limit, that’s all the State need to prove in order to prosecute you for drug driving.
Does cocaine instability provide an automatic defence?
No.
The fact that cocaine can break down does not automatically make an MBRS certificate unreliable.
It also does not automatically prove that the BZE result increased after the blood was taken.
A court is dealing with a particular blood sample, not a general scientific possibility.
The MBRS certificate is sufficient evidence of the facts stated in it unless the contrary is shown.1
A challenge therefore needs to be based on evidence connected to the individual specimen or the way it was analysed.
That might include evidence about:
· the dates and times involved;
· transport and storage;
· the temperature;
· the laboratory records;
· the analysis of the independent sample; or
· expert scientific evidence.
I have never seen such a case where evidence was presented to challenge the Bureau testing regime.
Ever.
The questions that matter in a real case
The following questions may need to be asked
1. When was the blood taken?
2. When did the sample arrive at the MBRS?
3. When was it analysed?
4. What evidence is available about its transport and storage?
5. Was an independent sample offered to the driver?
6. Was the independent sample tested?
7. Is there any evidence of a problem affecting this particular sample or analysis?
These are investigation questions.
They are not automatic defences.
Far from it.
The scientific studies explain why the history of a blood sample may matter.
They do not prove that any particular MBRS result is wrong.
Is independent testing worth it?
Not really. I'll explain below why I think so.
Cocaine can break down after blood has been taken. Some of it may turn into BZE.
The preservative in the Irish blood bottle is intended to slow that process. Storage time and temperature may still matter.
But the possibility of chemical change does not, by itself, defeat an MBRS certificate. Irish law allows the prosecution to rely on that certificate unless evidence is produced which shows the contrary.
So the real issue is not whether cocaine can change inside a blood bottle. We know that it can.
The important question is whether there is reliable evidence that something happened to the particular sample in the particular case.
No evidence has ever been produced to show that anything “untoward” has happened to a sample of blood or urine tested at the Bureau.
What if the sample shows signs of being interfered with or damaged on arrival at the Bureau?
They won’t test it.
Simple as that.
So should you get your own sample tested?
You can, but I don’t advise it.
I don’t advise it because I have confidence in the performance and standards of the Bureau.
Sources
1. Road Traffic Act 2010, revised
The legal limits are 10 ng/ml for cocaine and 50 ng/ml for BZE in whole blood. Section 20(3) deals with the evidential status of an MBRS certificate.
2. Isenschmid, Levine and Caplan, Journal of Analytical Toxicology, 1989
Controlled research into the stability and breakdown of cocaine. The study examined the effects of temperature, pH and preservatives.
3. Toennes and Kauert, Journal of Analytical Toxicology, 2001
A study of 147 cases comparing blood collected with and without fluoride and oxalate stabilising substances.
4. Brogan and others, Journal of Analytical Toxicology, 1992
An experiment examining sodium fluoride and refrigeration during 48 hours of storage.
5. Medical Bureau of Road Safety, FAQs and Guidelines
The MBRS explains that its blood bottles contain sodium fluoride and potassium oxalate.
6. Medical Bureau of Road Safety Annual Report 2025
Information about the Bureau’s toxicology work, quality system and ISO/IEC 17025 accreditation.
7. Giorgi and Meeker, Journal of Analytical Toxicology, 1995
A five-year study of drugs stored in blood tubes containing sodium fluoride and potassium oxalate.
8. Huertas and others, Journal of Analytical Toxicology, 2020
Research examining cocaine-related substances under different storage times and temperatures.
NOTE: This article provides general information. It does not reach any conclusion about an individual blood sample or criminal case.
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