Precision psychiatry promises a more objective and effective approach to psychiatric care, yet its implementation raises growing ethical challenges as technology advances. This narrative review offers a qualitative synthesis of the ethical issues reported in 62 studies, with emphasis on the practical tensions that arise when core principles conflict. Rather than organising concerns around traditional ethical principles, the review maps them across the main modalities of precision psychiatry, namely genomics, neuroimaging, digital phenotyping, and AI-driven interventions. Four explicit positions are advanced. First, equity must be engineered from the outset rather than assumed. Second, interpretability should outweigh marginal gains in accuracy in a field built on subjective report. Third, stigma is bidirectional and contingent on framing and the availability of meaningful intervention. Fourth, individualised care must demonstrate clinical and economic superiority over standardised approaches. Precision psychiatry is likely to reshape psychiatric practice and the therapeutic relationship itself. Interdisciplinary collaboration, clear guidelines, and continuous ethical vigilance will be essential for responsible adoption and sustained public trust.