As MHT acts by binding to oestrogen receptors (ER<i>α</i> and ER<i>β</i>), we used drug-target Mendelian randomisation (MR) to test whether perturbing these targets alters the risk of Alzheimer's disease (AD), brain structure, depression, or anxiety. The gene discussed is ESR1; the disease is early-onset autosomal dominant Alzheimer disease.