23/04/2026

We are receiving more queries from employers about prescribed medicinal cannabis, and it is increasingly featuring in tribunal claims.

Like any prescribed medicine, it can be lawful for an employee to use it. However, that does not give an employee the right to attend work impaired or to carry out safety‑critical duties if the medication could affect their ability to work safely.

This article summarises the key issues for employers.

1. What is the legal position?

In Northern Ireland, certain cannabis-based medicines can be lawfully prescribed and used. Cannabis remains a controlled drug where it is not prescribed. For employers, the key point is this: a lawful prescription does not override your health and safety duties, or your right to require staff to be fit for work.

Mishandling of this issue by employers can create liability for Tribunal claims such as disability discrimination and unfair dismissal.

Why this can be difficult: drug tests can show cannabis in the system long after any effects have worn off, and different products (and different THC/CBD levels) can affect people differently. The safest approach is to focus on evidence and risk, not assumptions.

Unlike alcohol (which many employers can ban entirely during working time), prescribed medication is harder to prohibit.

In practice, the question is whether the type of medication, the dose and timing, and the role create a real risk to performance or safety. That should be assessed using evidence and, where appropriate, medical advice.

2. Impairment and safety

Some medicinal cannabis products contain THC, which can affect performance. The impact will depend on the product, dose, how recently it was taken and the individual.

This is most relevant in safety‑critical work (for example, driving, operating machinery, construction, patient care, aviation and security roles).

You can require employees to be fit for work and to do their job safely. If someone is impaired, or if the role cannot safely be done while taking the medication, you can take action (which may include temporary adjustments, moving duties, or, in some cases, disciplinary steps).

3. Drug testing: what a positive result does (and doesn’t) prove

Drug testing is often where issues surface first. Most drug tests look for THC metabolites. That can create false confidence (or unfairness) because a positive test does not necessarily mean someone is impaired at the time of work.

• Tests usually cannot tell the difference between illegal cannabis and prescribed medicinal cannabis.
• THC can remain detectable for days (and sometimes longer), even when any effects have passed.
• A ‘positive’ should be treated as a trigger for investigation and risk assessment, not automatic misconduct.

Practical approach: if a test is positive, pause before deciding what happens next. For example:

1. Ask for evidence of a valid prescription (if the employee says the result is linked to prescribed use).
2. Consider the role and the risks (especially if it is safety‑critical).
3. Consider occupational health input and any medical evidence.
4. Carry out a health and safety risk assessment where appropriate and record the reasons for any decision.

4. Case law: what Tribunals focus on

There are now several Tribunal decisions involving cannabis and workplace drug testing. Many are from Great Britain, so they are not binding in Northern Ireland. However, they are a useful guide to how Tribunals approach fairness, evidence and adjustments.

• C Kimber v Cardiff and Vale University Local Health Board (Employment Tribunal, 2024): the Claimant succeeded in claims including unfair dismissal and disability‑related discrimination. It underlines the importance of investigating properly and considering medical evidence and adjustments, rather than relying on a positive test alone.
• Renewi UK Services Ltd v Pamment (EAT, 2021): this case demonstrates the risks of taking a “positive test = dismissal” approach. Tribunals will look for a fair investigation, consideration of the employee’s explanation (including health‑related reasons) and a reasonable and consistent application of the employer’s policy.
• Kuehne + Nagel Ltd v Cosgrove (EAT, 2014): the EAT emphasised the need to keep two questions separate: the employer’s reason for dismissal, and whether dismissal for that reason was fair. It also highlights how closely a Tribunal will examine the decision‑making process in drug‑testing cases.

Overall, the message is consistent: document your reasoning, take appropriate medical advice where medication is involved, and avoid blanket assumptions based solely on a positive result.

5. Disclosure and confidentiality

Employees do not usually need to share detailed medical information. However, if medication could affect safety, driving, machinery use or fitness for work, it is reasonable to require disclosure to a named HR or occupational health contact so you can assess risk and consider adjustments. Information about prescriptions and health conditions must be handled confidentially.

6. Disability and reasonable adjustments

If the employee says that the medication has been prescribed due to an underlying condition amount to a disability, the employer will need to make reasonable adjustments. The focus should be on whether the person can do the role safely and effectively, and what changes could help.

• temporary changes to duties (especially where work is safety-critical)
• alternative tasks or redeployment
• changes to shift patterns or start times
• homeworking where the role allows

Reasonable adjustments do not mean allowing someone to work while impaired or taking risks you cannot justify. Where safety is genuinely at stake, it may be reasonable to restrict certain duties or require medical advice before the employee returns to them.

7. Your policies: what to check and update

If your drug and alcohol policy was written mainly with illegal drug use in mind, it may not deal well with the issue of prescribed cannabis. We would advise to review your rules on medicines and fitness for work, and make clear what you expect in safety‑critical roles.

Where it is justified by risk, you can require employees in safety‑critical roles to disclose prescribed medication that could affect performance. If an employee fails to disclose and a “for cause” test later raises concerns, that may become a disciplinary issue. Take advice on the facts before acting.

Good policies focus on fitness for work and risk. They should encourage early, confidential disclosure of prescribed medication where safety could be affected, explain how testing will be handled, and make clear that being impaired at work is not acceptable (whatever the cause).

8. Handling a disclosure (or a positive test): a simple process

1. Keep it confidential. Limit information to those who need to know.
2. Confirm the facts. If prescribed use is claimed, ask for evidence of a valid prescription and basic information on the product and timing.
3. Assess the role and risks. Identify any safety‑critical tasks (for example, driving, machinery or lone working) and conduct a risk assessment.
4. Get medical input where needed. Occupational Health can advise on fitness for work and likely impact.
5. Put interim controls in place. This may include temporary changes to duties, hours, supervision or restrictions on safety‑critical tasks.
6. Review and record. Set review points and document decisions and reasons.

9. What employers should avoid

• Treating a positive test as automatic misconduct without looking at prescription and context
• Assuming a private prescription is “not genuine” or a loophole
• Blanket bans that take no account of disability and individual circumstances
• Sharing information about an employee’s medication more widely than necessary

10. Quick checklist

• Do we know which roles are safety-critical and what the specific risks are?
• Do our policies cover prescribed medication and fitness for work (not just illegal drug use)?
• Do managers know what to do if they suspect impairment?
• Does our testing process allow for confirmation, employee explanations and medical input?
• Do we have a clear, confidential route for employees to disclose prescriptions?
• Are decisions recorded with reasons (especially where duties are restricted)?

The safest approach is consistent: focus on fitness for work, assess risk based on the role, take medical advice where needed, and avoid snap decisions based on labels or assumptions.