This study uses the 2018 Canadian Internet Use Survey to examine reports of the negative effects individuals aged 15 to 64 experience because of their use of social networking websites or apps. Social media refers to digital platforms that allow users to create and share content (e.g., text-based posts, photos and videos) and online profiles, and to interact with other users. In 2018, social media was regularly used by about 9 in 10 Canadians aged 15 to 34, 8 in 10 of those aged 35 to 49, and 6 in 10 of those aged 50 to 64. Six outcomes attributed to social media use are examined: lost sleep, trouble concentrating on tasks or activities, less physical activity, feeling anxious or depressed, feeling envious of the lives of others, and feeling frustrated or angry. Among all social media users aged 15 to 64, around one-fifth reported that in the previous 12 months, they had lost sleep (19%), gotten less physical activity (22%), or had trouble concentrating on tasks or activities (18%) as a result of their social media use. Around one in eight users (12% to 14%) reported feeling anxious or depressed, frustrated or angry, or envious of the lives of others. Differences in the incidence of these outcomes across social media users in different age groups are of central interest. Compared with social media users in older age groups, larger shares of users in younger age groups report experiencing each of the six outcomes. In part, this reflects greater intensity of social media use among younger individuals, which is measured in terms of number of social media accounts used, number and types of social media activities undertaken, and intensity of smartphone use. After accounting for these characteristics, younger individuals remained significantly more likely than their older counterparts to report four of the six outcomes. Reports of lost sleep were especially prevalent among individuals aged 15 to 19, and trouble concentrating was especially prevalent among social media users aged 15 to 24. Reports of feeling anxious or depressed or of feeling envious of others were more prevalent among youth, broadly defined in this study as individuals aged 15 to 34. Reduced physical activity and feelings of frustration or anger did not vary across age groups once social media use characteristics were taken into account.