The honest answer is that we don't fully know the very long-term effects of hormone replacement therapy when taken for decades. Research is limited because we simply haven't had large numbers of people taking HRT for their entire adult lives to study the outcomes comprehensively. This applies to both transgender people and cisgender people going through menopause.
However, this uncertainty shouldn't be interpreted as danger. Evidence indicates that hormones are natural substances that our bodies are designed to use, and current research shows they provide significant benefits for bone health, cardiovascular health, and overall wellbeing. Guidelines recognise that people with testicles naturally maintain their hormones throughout most of their lives, whilst people with ovaries typically lose theirs around age fifty when their ovaries stop functioning.
Research shows that taking hormones long-term may well have positive effects that we haven't fully documented yet. The current evidence base suggests that the benefits of HRT significantly outweigh the risks for most people. Studies demonstrate improvements in bone density, reduced risk of osteoporosis, and better cardiovascular outcomes in many cases.
People often ask about these long-term effects because they want to make informed decisions about their health. Whilst we continue to gather more data through ongoing research, current medical understanding supports the safety and benefits of long-term hormone therapy when appropriately monitored and tailored to individual needs.