Side-effects of hormone replacement therapy and influence on pattern of use among women aged 45-64 years. The Norwegian Women and Cancer (NOWAC) study 1997

Background. Use of hormone replacement therapy (HRT) increased considerably in Norway during the 1990s. The aim of this study was to investigate reasons for starting and discontinuing HRT use and examine the prevalence of side-effects and what impact they had on pattern of use. Methods. The Norwegian Woman and Cancer (NOWAC) study is a population-based, prospective study based on mailed questionnaires to women 30-70 years. This report is limited to a random sample of 4996 Norwegian women aged 45-64 years who participated in 1997 (response rate 62%). The questionnaire included detailed questions about HRT: reasons for starting and stopping, type of preparation, duration of use and side-effects experienced. Results. Most women started HRT to ameliorate climacteric complaints (75.9%). Only 8.7% had prevention of osteoporosis as the only reason for therapy. Mean duration of use was 4.9 years among current users. Side-effects were reported by 43% of the ever users, nearly half of them reporting more than one side-effect. Weight gain was the most frequent stated side-effect (56.3%), although not statistically significant in association with HRT. Among ever users 28.2% discontinued therapy, more than half of them because of side-effects. Conclusions. The women's primary reason for starting HRT was climacteric complaints. Side-effects were common and constituted the major reason for discontinuation of therapy. The women perceived weight gain as a side-effect.