1.2.12 Drug screening

Because drug and alcohol abuse reduces safety and productivity and increases turnover and absenteeism, many employers use drug tests to screen employment candidates or determine if employees are working while under the influence of alcohol or drugs. Occupational health nurses play an important role in this testing process, as they oversee the collection and labelling of test samples.

Before the specimen collection process, the employee must sign a consent form. The consent form typically contains language indicating that the employee understands that refusing to take the test or tampering with the specimen is grounds for immediate dismissal. If it is a pre-employment drug test, the candidate acknowledges that no offer of employment will be made if the test is positive or if he refuses to take the test. Signing the consent form may also release the employer or the laboratory from any liability related to termination or other adverse job actions that may occur after a medical officer reviews the test result.

The specimen collection procedure may vary, but most employers use a similar process. After completing all required paperwork, the occupational health practitioner gives the employee a specimen container and provides instructions about collecting the specimen.

Despite claims from drugs-testing companies, there is no real evidence that drug-testing is becoming common-place in workplaces. It is mainly used, often with union agreement, in safety critical areas such as transport and energy generation or after an incident. There is also increased usage in the construction industry. However generally where wide-scale drug testing has been considered it has been rejected because of cost, union objections, or doubts over the effectiveness.

Most drug-testing methods do not actually test for the presence of drugs. This is because most drugs break down very quickly in the body. Therefore the test looks for the chemicals that remain after the drug breaks down. These are called the metabolites.

The metabolites of drugs can be detected in blood, urine, hair, sweat or saliva. The most common type of testing is urine.

The presence of drugs can be detected in urine, for most drugs, for up to three or four days after use, although in the case of some drugs they can be detected for up to 30 days, especially after heavy use. They can be detected in blood for roughly the same period or slightly less, and for an even shorter period in saliva. Most drugs can however be detected in hair for up to 90 days.

Different companies will test for different drugs but the most common package is a urine test for cannabis, cocaine, amphetamine, methamphetamine, benzodiazepine and opiates.

Unlike alcohol testing, what drug testing will not tell you is whether a person is either under the influence of a drug or what the level of impairment is. It will simply tell you whether the metabolites of a drug are present.

There are a considerable number of different types of drug test but they all work in a similar way. In the case of urine and saliva no preparation is needed but if blood is used the plasma has to be separated before testing. Hair is more complex to test because it has to be both washed and broken down.

The sample is then put through a screening test. These have various names such as ELISA and EMIT. They often produce ‘false positives’ so if a sample proves positive it should be subject to a confirmation test which is more precise but also quite expensive.

Even once a positive result is confirmed it should not be acted upon until the person who gave the sample has been interviewed by a medical doctor to find out if anything else could have resulted in the positive result.

Types of drugs testing

Pre-employment: This is when an employer screens all potential employees or applicants prior to them being employed. This is when people are at their most vulnerable because they are not employed and have far fewer employment rights, are not covered by grievance or appeals procedures and do not have the support of a union. Some job applicants have claimed that they have been denied employment because of a prescription drug they were taking but were not given the opportunity to challenge the result. This is the type of testing favoured by many companies because it is cheaper as it only needs to be done once, however it is also considered to be the least effective because, it is usually based on a urine sample. It is often easier to dilute or substitute the sample as it has to be given in private.

Post incident: This is when an employer tests employees after there is an incident that causes an injury, damage or a near miss. Sometimes this is done automatically after an incident, in other cases it is only done if the supervisor suspects that drugs may have played a part.

Random: Random testing involves selecting a number of employees at random at regular intervals and testing them. Drugs-testing companies claim that it is a major deterrent, although in the USA, where it is far more common, it has been claimed that users are more likely to switch from cannabis (which remains in the urine for much longer) to harder drugs which disappear from the system much quicker.


In the past, drug-testing was very unreliable. In recent years, testing has become more accurate and, if a sample is conducted by an approved laboratory and the sample is subject to a confirmation test, false positive results are now less common. That does not mean that drug-testing accurately indicates that a person has taken an illegal drug. In some cases, the metabolites of the drugs detected are the same, or similar, to drugs used in prescription or even over the counter medication. That means that a person can be given a positive result simply because they have taken a flu remedy.

Even when it does identify drug use correctly, what the test shows is simply whether the residues of a drug are present. It cannot tell with any certainty when the person took the drug, or whether they were under the influence of the drug.

So the biggest criticism of any form of drug-testing is that it does not tell an employer what they want to know, which is whether someone is, or was, under the influence of drugs while at work. It will, at best, tell you that the person is likely to have consumed a particular drug in the recent past.

Employers do have a duty to protect the safety of their workplace under the Act. That includes ensuring that employees are not working under the influence of drink of drugs.

No person can be forced to provide a sample of urine, hair, saliva or blood for any purpose. However, if a person has a contractual obligation to provide a sample, and refuses to do it, courts have ruled that, in certain circumstances that can be grounds for dismissal.

Even then consent should be given before a sample is taken but in practice it is very difficult for a person applying for a job, or if ordered to give a sample by their employer, to refuse so the concept of consent is meaningless.

Workers should also be entitled to privacy when giving a sample. The privacy issue is more commonly an issue when urine samples are used. Some employers have argued that another person should be in the room when a person is giving a sample to make sure it is not substituted or diluted. This is unreasonable, and a breach of human rights. In addition a number of people have an inability to pass urine in front of another person.

Good practice recommendations are:

  • Only use drug or alcohol testing where it provides significantly better evidence of impairment than other less intrusive means
  • Use the least intrusive forms of testing practicable to deliver the benefits to the business that the testing is intended to bring
  • Tell workers what drugs they are being tested for
  • Base any testing on reliable scientific evidence of the effect of particular substances on workers
  • Limit testing to those substances and the extent of exposure that will have a significant bearing on the purpose(s) for which the testing is conducted

A former worker with Amazon was awarded £3,453 in compensation after managers at the internet giant falsely told him he had tested positive for amphetamine and fired him. Khalid Elkhader was shocked when a random test was returned positive. He appealed and was asked to take a second test. Amazon claimed the test was also positive, and dismissed him for misconduct. It was only after he took Amazon to a tribunal that he learned the second test had actually been negative. He was awarded with compensation after the Glasgow tribunal ruled his sacking was unfair. Khalid was fired after working with the company for two years. The tribunal heard how he had tried to get the second sample tested by his own doctor, and arranged for it to be sent it to the lab. By the time a courier had arrived to collect the sample, it was too late and it had been destroyed. He then arranged for his own doctor to take a sample, which was also negative.


Those who oppose drugs-testing are often criticised as undermining the fight against drug use in the workplace. Any person who is under the influence of drugs while working can be a danger to both the worker and their colleague. However there is no evidence that introducing drug testing actually reduces injury rates.

More importantly it does not address the real issue, which is the ability of the worker to function safely. Unlike alcohol testing, drug-testing cannot tell you the likely effect of a drug on the person at a particular time. A more relevant test is an impairment test which gives an indication of whether a person’s abilities have been impaired by drink or drugs. This is sometimes used by police following a motor accident where a breathalyser test shows a negative result. These tests also do not just tell if a person’s abilities have been impaired by illegal drugs, but also by legal ones, which can be a bigger safety concern.

Where drugs are used in the workplace, they are often to combat either fatigue or stress. These should be addressed by removing the cause of the problem. In other cases a person will have a physical addiction to a substance – in which case they need help to address this.

The most effective way of ensuring that drugs are not a problem in the workplace is to have a comprehensive drugs and alcohol policy that seeks to support those that need help in a non-judgemental way.

There is an appeals process, with right to union representation, if anyone tests positive.