English summary 299 could also examine within-person differences between measurements when a participant used OCs compared to when participants were naturally cycling. The results from the overall group comparison showed no difference in depressive symptoms and depression diagnoses between measurements during OC use or naturally cycling. We also found no difference after accounting for whether participants had a previous or current mood disorder. Examining within-person differences, we did find that participants who had started or stopped OCs reported more depressive symptoms and a higher prevalence of depression diagnoses when using OCs compared to when they were naturally cycling. Altogether, we concluded that OC use could be associated with increases in depressive symptoms and increased risk of depression, but that there might be strong individual differences in the effects of OCs on mood. Gender-affirming hormone therapy In Chapter 3, we examined whether transgender persons who started GAHT experienced changes in depressive symptoms. We studied whether they reported a change in overall depressive symptoms, but we also examined specific groups of depressive symptoms, which we called "symptom clusters". For this study, we asked transgender individuals to report the extent to which they experienced depressive symptoms before starting GAHT, after 3 months of GAHT and after 12 months of GAHT. We then examined whether changes in depressive symptoms were different in participants who used masculinizing compared to feminizing GAHT. The group starting masculinizing hormones showed a relative decrease in depressive symptoms, whereas the group starting feminizing hormones showed a relative increase in depressive symptoms, resulting in a significant between-group difference in changes in overall depressive symptoms. This difference aligns with prevalence rates in cisgender populations, where we see a higher prevalence of depression in women compared to men. Examining the symptom clusters, we found that in participants who started masculinizing hormones, lethargy temporarily decreased after 3 months of hormone use, meaning these participants gained more energy and ability to concentrate, and that in participants who started feminizing hormones, symptoms of depressed mood increased slightly after 12 months of hormone use, meaning these participants reported more severe low mood. Altogether, the findings in this study suggest that masculinizing and
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