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Pharmacology Expertise

by Dr Paul Skett
(More about Dr Skett)

A pharmacologist is an expert who looks at drugs. A drug is defined as any substance that has an effect on the human body (so alcohol, solvents, etc. come into this category). A pharmacologist will consider:

  • What do the drugs do?
  • How do the drugs do what they do?
  • How are the drugs processed by the body?

and, ultimately

  • How does the body eliminate the drugs?

In answering the first two questions the pharmacologist will be considering pharmacodynamics; when answering the remaining questions the expert will be considering pharmacokinetics.


Definition: The study of the uptake into, distribution around and clearance from the body of drugs.

If you intend to argue either of the Road Traffic Act 1988 statutory defences (no intention to drive or post-incident drinking), you need an expert to calculate either:

  • if the stated intake of alcohol is consistent with the breath/blood level of alcohol found (post-incident drinking) or
  • when your client would be fit to drive again (i.e. below the statutory limit – no intention to drive defence).

You might also need such an expert if your client has used mouthwash (containing alcohol), sprays or inhalers (also containing alcohol), or may have ingested alcohol in any other form.

In these cases, the expert will need:

  • to know exactly how much alcohol was consumed (state type of alcohol and brand, if known)
  • to know exactly when the alcohol was consumed
  • details of the height and weight of the client
  • details of the timing of the incident
  • information about when the client was likely to drive again (no intention to drive), and
  • a copy of the breath/blood analysis report.

In other cases, it may be useful to know if your client was under the influence of any substance at the time of the alleged incident or during the police interview(s). This is much more difficult to calculate than with alcohol. However, knowing the same sort of information as above (height/weight of client, what drugs were taken, how much was taken and when), it is possible to calculate how likely it would be that the individual was under the influence of any substance. Of course, this also applies to the Road Traffic Act 1988 under the section(s) dealing with driving under the influence of drugs.

Such calculations can also be of use in civil cases (e.g. claims for damages due to a fall or medical negligence cases) where the fact that someone was under the influence of one or more drugs at the time of the alleged incident may affect what they did, said, saw, etc. Likewise, in Fatal Accident Inquiries (FAIs)/inquests, the ability to both forward- and back-calculate drug concentrations may be relevant in determining the cause of death.


Definition: The study of what a drug does and how it does it.

If you are arguing the case for possession/personal use of drugs under the Misuse of Drugs Act 1971, rather than supply, it is useful to have an expert report stating whether the amount in question could have been for personal use over a reasonable period of time. Note that abusers can become tolerant to fairly large doses of drugs, well in excess of what is used clinically.

In a more general sense, the known effects of drugs may be relevant to the case in point:

  • Could your client’s behaviour, or that of any other person involved in the alleged incident, have been influenced by drugs?
  • Could your client’s memory, or that of any of the witnesses, have been affected by drugs?
  • Could this be a case of drug-induced automatism?

In these cases it is important that the expert has as much information as possible about the drug use of the individuals concerned. Also essential is any witness evidence of the behaviour of the individuals concerned.

Individuals vary so much in their reaction to drugs that a combination of possible drug concentrations, with noted effects, often gives a better idea of whether the individual was under the influence of any substance at the material time. For example, if your client states that he took depressants (such as diazepam) but is seen running frantically around the street, these are inconsistent ‘facts’ – although diazepam can cause paradoxical aggression in rare cases, particularly when combined with alcohol.

Such considerations also spill over into civil cases. Does the fact that one or other of the parties could have been under the influence of alcohol or another drug (whether prescription, over-the-counter or recreational) have any bearing on the claim, given the effects of the substances in question?

Similarly in FAIs/inquests: What is, if any, the relevance of drug effects in determining the cause of death?

Drug Interactions

It is often forgotten that the effect of a certain drug can be altered by the presence of another. Most people recognise that you should not mix most drugs with alcohol. But why? What might the effects be of the combination?

Other drugs that affect the brain will also have unexpected effects if mixed together (e.g. amphetamine counteracts some of the effects of alcohol).

Overall, a pharmacologist can:

  • assist with any aspect of a drug’s effects or the clearance of drugs from the body
  • advise on how long a drug would act for and what the effects may be.
What a Pharmacologist is not

A pharmacologist is not a pharmacist. Thus he cannot assist with questions about the dispensing of medication.

A pharmacologist is not an analytical chemist. Thus he cannot discuss the chemical analysis of drugs – that is the job of a toxicologist. Having said that, some pharmacologists have expertise in interpreting the analysis of drugs.

In general a pharmacologist cannot assist with street prices, purity or availability of recreational drugs.


At a minimum, a pharmacologist should have a degree in a relevant subject – pharmacology or, perhaps, biochemistry, physiology or neuroscience. A research degree (PhD or MSc) in a relevant area is also to be recommended.

Most practising pharmacologists are members or fellows of the British Pharmacological Society.

by Dr Paul Skett
(More about Dr Skett)


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