The Coronavirus Disease 2019 (COVID-19) pandemic has exacerbated mental health challenges among physicians and non-physicians. However, it is unclear if the worsening mental health among physicians is due to specific occupational stressors, reflective of general societal stressors during the pandemic, or a combination. We evaluated the difference in mental health and addictions health service use between physicians and non-physicians, before and during the COVID-19 pandemic. We conducted a population-based cohort study in Ontario, Canada between March 11, 2017 and August 11, 2021 using data collected from Ontario's universal health system. Physicians were identified using registrations with the College of Physicians and Surgeons of Ontario between 1990 and 2020. Participants included 41,814 physicians and 12,054,070 non-physicians. We compared the first 18 months of the COVID-19 pandemic (March 11, 2020 to August 11, 2021) to the period before COVID-19 pandemic (March 11, 2017 to February 11, 2020). The primary outcome was mental health and addiction outpatient visits overall and subdivided into virtual versus in-person, psychiatrists versus family medicine and general practice clinicians. We used generalized estimating equations for the analyses. Pre-pandemic, after adjustment for age and sex, physicians had higher rates of psychiatry visits (aIRR 3.91 95% CI 3.55 to 4.30) and lower rates of family medicine visits (aIRR 0.62 95% CI 0.58 to 0.66) compared to non-physicians. During the first 18 months of the COVID-19 pandemic, the rate of outpatient mental health and addiction (MHA) visits increased by 23.2% in physicians (888.4 pre versus 1,094.7 during per 1,000 person-years, aIRR 1.39 95% CI 1.28 to 1.51) and 9.8% in non-physicians (615.5 pre versus 675.9 during per 1,000 person-years, aIRR 1.12 95% CI 1.09 to 1.14). Outpatient MHA and virtual care visits increased more among physicians than non-physicians during the first 18 months of the pandemic. Limitations include residual confounding between physician and non-physicians and challenges differentiating whether observed increases in MHA visits during the pandemic are due to stressors or changes in health care access. The first 18 months of the COVID-19 pandemic was associated with a larger increase in outpatient MHA visits in physicians than non-physicians. These findings suggest physicians may have had larger negative mental health during COVID-19 than the general population and highlight the need for increased access to mental health services and system level changes to promote physician wellness.