Benzoylecgonine Drug Driving

The legal limit for Benzoylecgonine is 50 micrograms per litre of blood (50ug). Any result showing Benzoylecgonine could be a false positive. If convicted, you would receive a 12 month driving disqualification. 

We can help you with:

  • Finding fault with police procedure
  • Challenging blood results 
  • Identifying defences
  • Next steps 

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Drug Driving & Benzoylecgonine

(inactive metabolite of cocaine)

Illegal Drug Legal Limit
Benzoylecgonine 50µg%

Cocaine is metabolised by our bodies very quickly. The rate of metabolism depends upon the concentration of the drug. There are three main routes by which cocaine gets ‘bio-transformed’ (broken-down);

  • Esterases
  • De-methylation
  • Ecgonine

The method that’s important to us is ‘De-methylation‘. This is the process whereby cocaine is metabolised into Benzoylecgonine (the primary inactive metabolite of cocaine). Around 40% of cocaine is metabolised into benzoylecgonine.

What is Benzoylecgonine (BZE)?

Benzoylecgonine is produced by the liver following cocaine consumption. It is known as a fingerprint metabolite because there is no other substance like it. A common misconception is that BZE is the substance commonly used as a bulking agent in cocaine. This is not correct. 

There are a few things to know about BZE. First of all, it's completely inactive. This means it doesn't cause any impairment whatsoever. Even high levels of Benzoylecgonine (400 - 800 micrograms) would have no effect on you. The reason the government chose to include BZE within the prescribed limits is because it remains in your system for much longer than cocaine. Ministers were concerned that by the time a person is processed at a police station and provides a blood test, the cocaine will been eliminated (meaning a person escapes a prosecution). Benzoylecgonine is almost certainly present because it remains in your system for much longer than cocaine (see below). 

How long does Benzoylecgonine stay in your system?

Cocaine is eliminated from your blood within 4 – 6 hours, whereas  benzoylecgonine can be present for up to 6 days after administration.

Benzoylecgonine is detectable in your blood within 30 minutes of cocaine consumption. This amount will then rise gradually over the next 2 – 3 hours. So, if you were to ‘sniff’ a 35mg line of cocaine at 10:00pm, Benzoylecgonine would be detectable by 10:30pm. By 01:30am, this will have rose to 130 micrograms (the legal limit is 50 micrograms).

Benzoylecgonine Defences

The prescribed limit for Benzoylecgonine is approximately 400,000 times lower than the drink driving limit! This is because most drugs, including BZE, can only be found in very small quantities. This makes testing blood for BZE an extremely difficult and technical process. It is one of the reasons why blood results produced by police laboratories are not always accurate when it comes to benzoylecgonine drug driving cases. 

We do not intend to ‘spill our trade secrets’ on here, but we’re quite happy to outline the five key aspects of a Benzoylecgonine drug driving defence.

Benzoylecgonine can be found in tap water!

Believe it or not, a recent study conducted by The Drinking Water Inspectorate found high levels of Benzoylecgonine in drinking water! The research was carried out by scientists to look into the dangers of drug compounds to the national supply. It seems that even robust water treatment plants cannot completely remove Benzoylecgonine from our water supplies. 

Whilst the research found that levels of BZE were very low, it is not know whether this could put a motorist over the prescribed limit (bearing in mind the UK drug driving limits are 'zero tolerance'.)

Benzoylecgonine levels increase overtime

Benzoylecgonine (BE) is the primary metabolite of cocaine and is commonly tested in forensic toxicology. The increase in benzoylecgonine concentration over time in stored blood samples can be attributed to the hydrolysis of cocaine into benzoylecgonine, particularly under certain storage conditions.

Mechanism of Cocaine to Benzoylecgonine Conversion in Stored Blood Samples

Cocaine undergoes spontaneous and enzymatic hydrolysis to form benzoylecgonine. This process can continue even after blood has been drawn and stored, leading to an increase in benzoylecgonine levels over time. The key factors contributing to this phenomenon include:

  1. Ester Hydrolysis

    • Cocaine is an ester and is hydrolyzed into benzoylecgonine in the presence of water.
    • This reaction occurs non-enzymatically in aqueous solutions, including blood samples, even after collection.
    • The hydrolysis is accelerated in alkaline conditions but can also proceed at neutral pH.

  2. Enzymatic Breakdown (Post-Collection Activity)

    • In living systems, cocaine is metabolized to benzoylecgonine primarily by liver and plasma esterases (such as carboxylesterase).
    • In stored blood samples, some enzyme activity may persist for a time after collection, contributing to continued metabolism.

  3. Storage Conditions Impacting the Conversion

    • Temperature: Higher temperatures can accelerate hydrolysis, leading to a faster increase in benzoylecgonine levels.
    • pH Levels: Slight alkalinity favors the hydrolysis of cocaine to benzoylecgonine.
    • Time: The longer the sample is stored, the greater the potential increase in benzoylecgonine concentration.
    • Preservatives: The presence or absence of preservatives (e.g., sodium fluoride) can influence the rate of cocaine degradation. Fluoride helps inhibit esterase activity, slowing the conversion.

Forensic Implications

Since benzoylecgonine levels can increase due to post-collection hydrolysis, forensic toxicologists must carefully consider storage conditions when interpreting results. The increase in benzoylecgonine (BZE) concentration in stored blood samples can be quantified to some extent, but the exact amount depends on several factors, including storage time, temperature, pH, and presence of preservatives.

Research Findings on BE Increase Over Time

  1. Temperature-Dependent Increase

    • Room Temperature (~20-25°C): Cocaine hydrolyzes relatively quickly to benzoylecgonine. Studies suggest that BE concentrations can increase by 50-100% within a few days if the sample is left at room temperature!!
    • Refrigerated (4°C): Hydrolysis slows down significantly, but BE can still increase by 10-20% over a week!!

  2. Time-Dependent Increase

    • BZE concentration tends to increase significantly within the first 24-48 hours in unpreserved blood at room temperature.
    • Over 1-2 weeks, BZE levels can double or even triple in poorly stored samples.

  3. Effect of Preservatives (e.g., Sodium Fluoride)

    • Even when adding preservatives, BZE levels can still increase by 10-30% over weeks instead of doubling or tripling.

Key Takeaways

  • At room temperature, BE can increase significantly (~50-100% in a few days).
  • Refrigeration slows the increase (~10-20% per week).
  • Freezing (-20°C or below) minimizes the increase (~5-10% over months).

One of the most effective defences we use relates to the post-sampling decomposition of Cocaine. Once a blood sample is taken by a Health Care Professional it remains in storage for up to 5 months before being analysed. Police storage facilities are often over-used, poorly maintained and dirty. Some police officers store their lunch in the same fridges used to store samples!! This is not a suitable environment for an evidential sample of blood. Overtime a blood sample will deteriorate (due to bacterial action and enzymes in the blood). You cannot stop this process but you can slow it down by adding preservatives. In most cases the deterioration of blood will benefit the suspect (because the drug levels will also fall). However, Benzoylecgonine is different. As Cocaine levels drop, it converts into Benzoylecgonine. Cocaine diminishes by 30% in three weeks of storage. 20 micrograms of Cocaine will convert into roughly 10 micrograms of Benzoylecgonine. Imagine what 5 months of storage will do... 

  • I received dental treatment and used Benzocaine. Can this cause a false positive? 


    Benzoylecgonine is one of three metabolites of Cocaine. It is not found anywhere else on earth! This means that if BZE is detected it almost certainly proves some prior use of Cocaine (assuming the result is not false). Benzocaine cannot produce Benzoylecgonine. However it is, in theory, possible that an inexperienced lab worker might mistake Benzocaine for Benzoylecgonine - giving you a complete defence. If you were receiving dental treatment, please let us know. 

  • False Positives

    Cocaine metabolises into Benzoylecgonine. This process cannot be stopped, only slowed. Police-issued blood vials should be pre-coated with a preservative and anti-coagulant (assuming the police use the correct vials). We are often able to prove that the proportion of Benzoylecgonine in the suspect’s blood was below the legal limit at the time it was taken but, due to the conversion between Cocaine and Benzoylecgonine, the Cocaine continues to metabolise pushing the BZE levels above the legal limit when the sample is finally tested.

  • Method of Analysis

    The most common method of analysis for Benzoylecgonine is Gas-Chromotography Mass-Spectometry (GC-MS). This is considered the ‘gold standard’ in commercial drug testing. GC-MS is a specialised analytical method that, until recently, wasn’t offered by many laboratories due to its complex (and expensive) ‘two-stage’ analytical process. It enables scientists to identify and quantify individual metabolites within a blood sample.

    Despite this method being one of the most accurate ‘large scale’ analytical methods, the laboratory are still required to deduct 20% from the measured result to allow for ‘normal analytical variation’. If this method of analysis is as accurate as the experts say, there would be no requirement to reduce the result by 20%. This indicates the potential for unreliable results.  If the laboratory has failed to deduct this amount, you could be wrongly (and unfairly) charged with drug driving.

  • Quality Control and Quality Assurance Procedures

    Laboratories wishing to undertake drug testing of this type are required to attain a specific accreditation by the United Kingdom Accreditation Service (UKAS). Part of this validation process requires laboratories to frequently measure their analytical performance in terms of accuracy and precision (due to the huge margin for error with drug analysis).

    M.A.J. Law has recently received information that a leading UK laboratory has failed a number of quality control and assurance tests. It has been confirmed that a large amount of results were incorrectly calculated due to a ‘data anomaly’. The same laboratory has since had its accreditation withdrawn.

    Benzoylecgonine is a ‘fingerprint metabolite’. This means that no other drug or prescription medicine produces exactly the same metabolite. However, some medicines produce metabolites that are similar in structure. Laboratories who don’t enforce a strict quality control procedure could mistakenly detect what thy believe to be benzoylecgonine, when in fact it’s nothing more than a prescription medicine.