Testosterone cypionate is a synthetic form of testosterone commonly used in hormone replacement therapy for transgender men (assigned female at birth) as part of gender-affirming care to masculinise secondary sexual characteristics. Here are potential unwanted/adverse/side effects of testosterone cypionate injections in the context of gender-affirming care:
| Side Effect | Description |
| Breast tenderness and enlargement | Estrogen therapy stimulates breast tissue development, leading to breast tenderness and enlargement. |
| Fat redistribution | Estrogen therapy may lead to changes in fat distribution, resulting in a more feminine body shape with increased fat deposition in the hips, thighs, and buttocks. |
| Reduction in muscle mass | Estrogen therapy may lead to a decrease in muscle mass and strength. |
| Decreased libido | Some individuals may experience a decrease in libido (sex drive) as a side effect of estrogen therapy. |
| Erectile dysfunction | Estrogen therapy may cause erectile dysfunction in transgender women. |
| Mood changes | Estrogen therapy may lead to mood changes, including mood swings, irritability, or changes in emotional well-being. |
| Hot flashes | Some individuals may experience hot flashes as a side effect of estrogen therapy. |
| Weight gain | Estrogen therapy may lead to weight gain, particularly due to changes in fat distribution. |
| Decreased fertility | Estrogen therapy may decrease sperm production and fertility in transgender women. |
| Increased risk of blood clots | Estrogen therapy may increase the risk of blood clots, including deep vein thrombosis (DVT) and pulmonary embolism (PE). |
| Increased risk of breast cancer | Long-term estrogen therapy may increase the risk of breast cancer, although the absolute risk is relatively low. |
| Increased risk of cardiovascular disease | Estrogen therapy may increase the risk of cardiovascular disease, including heart attacks and strokes, particularly in individuals with pre-existing risk factors such as smoking, obesity, or hypertension. |
| Gastrointestinal symptoms | Some individuals may experience gastrointestinal symptoms such as nausea or bloating as a side effect of estrogen therapy. |
| Changes in cholesterol levels | Estrogen therapy may affect cholesterol levels, leading to decreases in LDL cholesterol (“bad” cholesterol) and increases in HDL cholesterol (“good” cholesterol). |