The social conditions created by the COVID-19 pandemic had a great potential to affect the mental health of individuals. Meta-analyses indicate a rise in these problems in these periods among general populations, patients and health professionals, even with substantial heterogeneous results. This paper examines mental health impacts specifically during the first wave of COVID-19. An online survey was conducted with a Portuguese convenience sample (N = 1.062) comprising questions about substance use, perceived stress, post-traumatic stress disorder and self-damage behaviors. The results concerning substance use show an extensive use of medication to sleep or calm down, especially among women and older respondents, a small percentage of alcohol consumers with a high pattern of use and less frequent cannabis consumption, even with a quarter of users who began only in the COVID-19 period. The rates of perceived stress and PTSD were higher compared with international prevalence estimations during the pandemic conditions. Both correlated measures were worse for women and young people. Another problematic issue was the rate of suicidal ideation, with a relevant proportion of starters during this period. These data reinforce the need to promote access to mental health services.