Side effects can occur fairly soon after starting HRT and usually wear off within one to three months. HRT side effects can include headaches, vaginal spotting, nausea, breast tenderness, and tummy (abdominal) pain. Some may notice mild bloating or ankle swelling due to fluid retention in the first few weeks, but this should settle fairly quickly. HRT that is applied to the skin may cause skin reactions. This is more likely with patches, which contain an adhesive. Always read the information leaflet that comes with your medication, particularly the section on side effects. Read more about HRT and side effects.