RESEARCHER PROFILES: Dr Tim Laurens and Prof Pieter Carstens

30 March 2021 by Prof Pieter Carstens and Dr Tim Laurens

Dr JB (Tim) Laurens, who has the distinction of holding two PhDs (Chemistry and Medical Law), was until recently a senior lecturer and manager of the Forensic Toxicology Laboratory at UP. He is also a director of the private company Point-of-Care Technologies, which specialises in drug testing and related technologies.

Dr Laurens has 39 years’ experience in forensic toxicology and has acted as a consultant for the United Nations on forensic laboratories in Africa as well as for the Department of Health on matters related to forensic toxicology. He also acts as an expert witness in South African courts and has published more than 20 articles in international peer-reviewed scientific journals.

His colleague and former promoter, Prof PA (Pieter) Carstens, is a professor of criminal and medical law. He served as Head of UP’s Department of Public Law for several years and holds a doctorate in medical malpractice law.

Prof Carstens is an advocate of the High Court of South Africa, is an extraordinary professor in the Department of Forensic Medicine at UP and is chairperson of the Unit for Medicine and Law, a joint venture between UP and UNISA.

Diagnosed with cancer nearly five years ago, Prof Carstens is a supporter of physician-assisted suicide and believes there is a need to harmonise the Constitution, common law and medical ethics to ensure the right of patients to die with dignity.


1. The legalisation of dagga has created some grey areas for both employers and employees due to potential conflict with the Occupational Safety and Health Act and the Machinery and Occupational Safety Act, which prohibit intoxicating liquor and drugs in the workplace. Have they been amended to take into account the legalisation of cannabis?

The two acts have not been revised. A revision is urgently required and should address the minimum requirements for a workplace drug testing policy in general, which should encompass the legal, ethical and scientific issues as there are no formal guidelines in South Africa for workplace drug testing. Threshold levels for drugs must also be specified as well as standardised detection techniques.    

2. What are some of the practical difficulties facing both employers and employees due to cannabis legalisation? Could there be a situation where an employee would effectively be prevented from ever smoking or consuming dagga over a weekend or after work?

The legal challenges will probably dominate this field for a long time at first. If an employer insists on a zero-concentration approach, the employee could end up in a situation where he cannot exercise his freedom (including freedom of religion for some) and autonomy to use a legal substance responsibly.

Employers will have to motivate why such a low threshold concentration was chosen. An individual might be fit to exercise their duty at a concentration level of 2ng/ml blood/serum or oral fluid. Blood sampling is invasive, and oral fluid is problematic to sample correctly due to buccal cavity contamination.

The same applies to alcohol use, where it is legal to drive on a public road with alcohol in our system below a specific threshold; however, many employers prefer a zero-concentration threshold for alcohol. The difference between alcohol and THC [tetrahydrocannabinol] is the much longer half-life for the latter.

A crucial matter is that all non-negative screening test results have to be confirmed in a forensic toxicology laboratory. 

3.  In trying to strike a balance between the interests of employers and employees on this issue, what is your advice when it comes to company contracts relating to the use of dagga, including situations where employees work from home during pandemic lockdowns?

All parties should have the same goals, which must be formulated in the policy. The main aim is to minimise risks in the interest of everybody's health and safety, and the organisation's interests (financial, etc.) to the benefit of all.

A low threshold (ca 2ng/ml) will strike a balance between the health and safety (and the individual) of others and the individual's fundamental human rights. People working from home must be aware that they might be requested to submit a specimen at any time during the shift.

4. In your recent research paper in the SA Medical Journal, you discussed a range of legal concentration thresholds that might offer a suitable “compromise” and would permit an employee to consume dagga in private, without harming the interests of the employer. What do you suggest would be a reasonable concentration threshold?

This depends on the type of sampling device employed. A threshold concentration of 2ng/ml to 5ng/ml is a suitable minimum threshold concentration for oral fluid, and 15ng/ml THC-COOH in urine, as the possibility of passive inhalation needs to be excluded. Only active intake should be prohibited.

5. Why do you believe it is important for employers to understand the distinction between a “zero-tolerance” and “zero-concentration” approach on this issue in the workplace?

A zero-tolerance stance is not the same as a zero-concentration threshold. The first is a stance against drug and alcohol use, which increase risk in the workplace, while the latter is a physical quantity that must be chosen in a legally defensible way. Zero-concentration levels would require information on the lowest concentration detected by a specific device (limit-of-detection or LOD). The LOD of different devices and brands also differ. Employees are sometimes tested with different brands and devices, impinging on the right to equality and amounts to discrimination. Many employers are utterly ignorant to this fact. 

6. There are pros and cons to different methodologies when testing for dagga in the workplace (such as blood, urine or saliva). On balance, which of these methods would you favour?

Blood is invasive, but urine and oral fluid may serve as a proxy for blood if the test is performed correctly. Urine and oral fluid testing complement each other in a testing regime since urine testing can be employed to manage longer-term risk, while oral fluid can be used to detect recent use (hours) before a subject enters the premises. These cases may go undetected if only urine is tested.

7. Could an employee successfully sue his/her employer on the basis that an employment contract (new or existing) prohibiting any trace of dagga is an unlawful infringement of their constitutional rights?

Dr Laurens: I think it will be possible in principle. However, the limitation must be reasonable and justifiable according to section 36 of the Constitution. A concentration below 2ng/ml has been shown not to have an impairment on an individual. However, it does place a problematic responsibility on the employer to test these levels reliably and accurately if they set a threshold concentration at “zero” concentration (limit-of-detection).

Prof Carstens: I agree, in principle, with the possible infringement in terms of the Constitution (in the context of the limitation clause as per section 36 of the Constitution). However, this issue will have to be addressed by all the relevant stakeholders, and in the end, be regulated by the relevant legislation and regulations.

With regard to smoking at home (“home” now being the workplace for many), I think one would be able to smoke in the privacy of one’s own home (in line with the stipulations of the legislation on smoking). It should be remembered that the legislator does not make laws that would lead to absurdities.

8. Dr Laurens, you have the distinction of holding two PhDs. What factors influenced your decision to invest extra time and effort to gain a "double doctorate", and would you encourage other academics to follow this path?

I work in the forensic toxicology field, which is always entangled with the law, since testing is mostly done on humans (with rights). I encourage other academics to follow this path if the opportunity arises.   

As a chemist, it is essential to be aware of and find the natural sciences' applications in other disciplines. In this way, we can make a real contribution to humankind's well-being, which will reap the benefit of combining knowledge from the two disciplines. Doing two doctorates enhance a person's vision and makes you realise again how little you know. It also helps to respect and appreciate individuals' efforts and knowledge working and specialising in other disciplines.

Prof Pieter Carstens (left) and Dr Tim Laurens (right)