Heat, Medication, and Outdoor Workers: A Summer Concern Hidden in IMEs

A worker on an SSRI doing residential roofing in July is at a different risk profile than the worker beside him on no medication at all. Most files won't say that out loud. Most IMEs won't ask.

That's a problem when the season comes around again.

The pattern WorkSafeBC keeps seeing

Between 2020 and 2024, WorkSafeBC accepted 315 heat-related injury claims. The peak year was 2021 - the heat dome summer - which alone accounted for 113 of them. The claims clustered in predictable industries: transportation, construction, public works, food services, and film and television.

But the 2021 spike obscured something quieter. Heat claims didn't disappear after the dome ended. WorkSafeBC accepted 49 in 2023 and another wave through 2024, and BC's Occupational Health and Safety Regulation now codifies employer duties around heat exposure in Sections 7.27 through 7.32. WorkSafeBC has issued public warnings every summer since 2023 reminding employers that heat exposure isn't a freak-weather risk - it's a baseline operational one.

For case managers, adjusters, and IME providers, the file pattern has shifted. Heat-related illness is showing up in claims that don't lead with heat as the mechanism - cardiac events, dehydration-driven kidney injury, falls from heat exhaustion, and acute mental health presentations among outdoor workers.

Context worth keeping in mind: the 2021 BC heat dome was linked to 619 deaths province-wide according to the BC Coroners Service, the deadliest weather event in Canadian history. The compensable injury claims WorkSafeBC accepted represent the surviving, employed slice of a much larger public health picture. The infrastructure that exposes claimants - outdoor work environments, vehicles, unconditioned interiors - isn't going away, and Environment and Climate Change Canada has been clear that heat events are increasing in frequency.

The medication piece almost nobody asks about

Here's where it gets interesting from an IME standpoint.

A 2024 systematic review and meta-analysis published in eClinicalMedicine confirmed what occupational health practitioners have known clinically for years: multiple medication classes meaningfully change how the body regulates temperature.

The big ones:

1. Antihistamines and decongestants - even over-the-counter ones - have anticholinergic effects that can inhibit sweating. A worker on diphenhydramine for seasonal allergies has a measurably reduced ability to cool down.
2. Antidepressants split in different directions. SSRIs and SNRIs can increase sweating and accelerate dehydration. Tricyclic antidepressants can suppress sweating. Both directions create risk in heat, just through different mechanisms.
3. Antipsychotics can interfere with the hypothalamus, blunting the body's core temperature regulation entirely.
4. Diuretics, beta-blockers, and certain blood pressure medications change cardiovascular response to heat stress.

None of this is exotic. These are some of the most commonly prescribed medication classes in Canada. The U.S. CDC has published clinical guidance specifically on heat and medication interactions, and Health Canada has flagged similar risks. But in standard IMEs of outdoor workers, medication-heat interactions are rarely part of the clinical conversation.

Where it shows up in the file

This matters in two directions.

First, in causation analysis. A heat-related event in a worker on relevant medication isn't necessarily "just heat" - it's heat in interaction with a pharmacological vulnerability that may or may not have been disclosed to the employer. The IME that flags this contributes to a more accurate picture of what actually happened.

Second, in return-to-work planning. A worker who's had a heat event, is returning to outdoor work, and remains on medication that affects thermoregulation needs specific accommodation - not a generic "stay hydrated" memo. The CFC and RTW recommendations should reflect that.

A concrete example: a 47-year-old paving crew member on lisinopril and an SSRI experiences a syncopal episode at midday in late July. Standard IME framing might land on "resolved heat exhaustion, fit for full duties." A more thorough framing flags the medication profile, recommends graduated re-entry with heat exposure limits, prompts a conversation with the prescriber about timing of medication, and identifies the worker as elevated-risk for future events. Same claimant, very different return.

What to look for in the assessment

A few things worth flagging when commissioning an IME on an outdoor worker post-heat event - or pre-empting one in a high-risk file:

• A current medication list, including OTC products and supplements (not just prescription).
• Specific clinical commentary on heat tolerance given the medication profile.
• RTW recommendations that account for thermal load, not just functional capacity.
• Where relevant, recommendations on consultation with the prescribing physician about timing, dosing, or alternatives during peak heat months.

The bottom line

Heat illness is no longer a one-summer-in-five risk in BC and Western Canada. It's a recurring file pattern, and it's tangled up with medications most claimants take without thinking about it. IMEs that surface that interaction give adjusters, case managers, and counsel a clearer picture - and give workers a safer return to work.

The conversation is worth having before the next heat advisory lands, not after another claim is opened. Files built with thermoregulatory risk in mind from the start tend to age better than files that have to be reopened mid-summer when something predictable happens.

Sources

WorkSafeBC heat stress: worksafebc.com

WorkSafeBC 2025 news release on heat illness: worksafebc.com news release

eClinicalMedicine 2024 meta-analysis on medications and core temperature: thelancet.com

CDC Heat and Medications clinical guidance: cdc.gov