Conducting a Medical Risk Assessment for Prescribed Cannabis in the Workplace.

Medical cannabis is legal in the UK when prescribed by a specialist doctor. That is a fact.

But here is another fact that often gets missed:

Legal does not automatically mean safe for work.

As employers, we have a duty to balance two things properly:

• Supporting employees who have legitimate medical needs

• Protecting the safety of the individual, their colleagues, and the business

This is where a structured, fair, and legally sound medical risk assessment becomes essential.

First Principle: Legal Status Is Not the Same as Fitness for Work

Let’s deal with the uncomfortable truth.

An employee can be lawfully prescribed cannabis and still be impaired at work.

The same applies to:

• Morphine

• Codeine

• Diazepam

• Strong antihistamines

• Even some antidepressants

Here’s the comparison most people understand immediately:

Alcohol is legal. However, driving under the influence of alcohol is not.

In exactly the same way that prescribed cannabis is legal but being impaired at work because of it is not acceptable in a safety-critical environment.

Your responsibility as an employer is not to judge the prescription. It is to assess the risk.

Step 1: Do Not Panic and Do Not Discriminate

If an employee discloses prescribed cannabis use:

• Do not suspend automatically

• Do not assume impairment

• Do not treat them as a disciplinary issue

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Instead treat it as a medical declaration requiring a workplace risk assessment.

Remember:

• The employee may be protected under the Equality Act 2010 if their underlying condition qualifies as a disability.

• The focus must be on safety and reasonable adjustments, not punishment.

Step 2: Gather Relevant Information (Confidentially)

This is not about asking for medical records. It is about understanding risk.

Areas you should explore:

• What condition is being treated?

• What form is prescribed? (Oil, flower, capsule)

• What dosage and frequency?

• What are the known side effects?

• Has the prescribing clinician provided guidance about driving or operating machinery?

If needed, request occupational health input. You are assessing functional impact, not moral judgement.

Step 3: Assess the Role, Not Just the Person

Risk is role-dependent.

Consider asking:

• Is the employee in a safety-critical role?

• Do they operate machinery?

• Do they drive?

• Do they work at height?

• Are they responsible for vulnerable people?

• Could impaired judgement cause serious harm?

Someone working remotely in a desk-based analytical role carries very different risk from someone driving a forklift truck. The same prescription may be low risk in one role and high risk in another.

Step 4: Understand Impairment vs Detection

This is where many organisations get it wrong. A drug test may detect THC metabolites days or weeks after use.That does not prove impairment at the time of work.

However:

Acute effects of THC can include:

• Slowed reaction time

• Reduced coordination

• Impaired concentration

• Altered perception

• Fatigue

Your risk assessment must focus on “Is there a realistic possibility of impairment during working hours?” Not “Will a test show a positive result?”

They are two very different questions.

Step 5: Consider Timing and Adjustments

In many cases such as this, risk needs to be managed rather than eliminated.

Consider the following:

• Can dosing be scheduled outside working hours?

• Can shifts be adjusted?

• Can temporary alternative duties be provided?

• Can high-risk tasks be restricted during initial treatment stages?

Remember the alcohol comparison:

If someone has a drink at 8pm and is sober at 8am, there is no issue.If someone drinks at 7am and operates machinery at 8am, there could be a serious problem. The same logic applies here. The issue is not legality, it is impairment during working hours.

Step 6: Document Everything

Your medical risk assessment should include:

• Disclosure date

• Information considered

• Role risk factors

• Occupational health input (if obtained)

• Agreed adjustments

• Review date

Make it clear:

• The employee must not attend work impaired

• The policy applies equally to alcohol, prescription medication, and illicit substances

Consistency protects everyone.

Step 7: Review Regularly

Prescriptions change, tolerance changes, roles change.

Make sure to set review dates, particularly:

• When treatment begins

• When dosage changes

• If there are any observable performance concerns

Risk management is not a one-off event.

The Hard Truth Employers Must Understand

Some businesses swing too far one way, “It's prescribed. We can’t touch it.” Others can swing too far the other: “Cannabis equals dismissal.”

Both positions are flawed.

Your obligation and responsibility is not to approve or condemn medical cannabis. Your obligation is to ensure that no one is impaired while carrying out work that could cause harm.

That standard applies equally to:

• Alcohol

• Prescription opioids

• Sedatives

• And prescribed cannabis

If you would not allow someone to operate heavy machinery after drinking alcohol, even though alcohol is legal, then you cannot ignore impairment risk from prescribed cannabis either.

A Smarter, Safer Approach

The correct approach is balanced and professional:

• Support the individual

• Respect medical privacy

• Avoid discrimination

• Assess risk objectively

• Manage impairment, not morality

Workplace safety is about fitness for duty, not personal choices. Prescribed cannabis is legal in the UK.Workplace impairment is not acceptable. There is a difference and, as leaders, we must understand it. If you want your workplace policies to reflect that balance properly, the assessment process needs to be clear, structured and defensible.

That is how you protect your people, and your business, at the same time.

That’s better testing.