Effects of over-the-counter antihistamines on heat stress

Do Common Over-the-counter Antihistamine Medications Modify Thermoregulatory Responses During Passive Heat Stress?

PHASE4 · Lakehead University · NCT06217367

This study tests whether common allergy medications can affect how well young adults handle heat stress and sweating during hot weather.

Quick facts

PhasePHASE4
Study typeInterventional
Enrollment16 (estimated)
Ages19 Years to 39 Years
SexAll
SponsorLakehead University (other)
Locations1 site (Thunder Bay, Ontario)
Trial IDNCT06217367 on ClinicalTrials.gov

What this trial studies

This study investigates the impact of over-the-counter antihistamines on individuals experiencing heat stress and allergic rhinitis. It aims to determine whether commonly used antihistamines, such as diphenhydramine, loratadine, and desloratadine, affect thermoregulation and sweating during heat exposure. Participants aged 19 to 39 will be administered either antihistamines or a placebo to assess their physiological responses to heat stress. The study seeks to clarify public health concerns regarding antihistamine use during heat waves.

Who should consider this trial

Good fit: Ideal candidates for this study are healthy males and females aged 19 to 39 with a body mass index under 30 who are fully vaccinated against COVID-19.

Not a fit: Patients with a body mass index over 30 or those with certain medical histories, such as cardiovascular disease or diabetes, may not benefit from this study.

Why it matters

Potential benefit: If successful, this study could provide evidence supporting the safe use of antihistamines during heat waves, improving quality of life for individuals with allergic rhinitis.

How similar studies have performed: While previous studies have shown that high doses of antihistamines can reduce sweating, this study explores their effects in typical over-the-counter dosages, making it a novel approach.

Eligibility criteria

Show full inclusion / exclusion criteria
Inclusion Criteria:

* Male or Female between ages 19 and 39 years
* Fully vaccinated against COVID-19
* Able to provide informed consent
* Body-mass index under 30

Exclusion Criteria:

* Body-mass index over 30
* Currently taking sedative or autonomic nervous system depressant medication
* Hypersensitivity to diphenhydramine, loratadine, or desloratadine
* History of cardiovascular disease, cancer, type 1 or 2 diabetes, chronic obstructive pulmonary disorder, or cystic fibrosis
* Have smoked tobacco products less than 12 months prior to participation
* Pregnant/Breastfeeding

Where this trial is running

Thunder Bay, Ontario

Study contacts

How to participate

  1. Review the eligibility criteria above with your treating physician.
  2. Visit the official trial page on ClinicalTrials.gov for the most current contact information and recruitment status.
  3. Contact the listed study coordinator or principal investigator to request pre-screening. Pre-screening is free and never obligates you to enroll.

View on ClinicalTrials.gov →

Conditions: Heat Illness, Allergic Rhinitis, Heat Injury, Sudomotor Sympathetic Dysfunction, H1 antihistamine, Sweating, Heat stress, Thermoregulation

Last reviewed 2026-05-15 by the Find a Trial editorial team. Information on this page is for educational purposes and is not medical advice. Always consult qualified healthcare professionals about clinical trial participation.