Introduction
Hormones and sex drive
Hormones and sexual orientation
Brain structure and sexual orientation
Important considerations
References
Further reading
Hormones play a key role in regulating libido and contribute to brain development before birth, but current evidence indicates that adult hormone levels do not determine sexual orientation. Research suggests that sexual orientation arises from complex interactions among prenatal hormonal influences, genetics, neurodevelopment, and environmental factors.
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Introduction
Sex drive or libido refers to the motivation for sexual activity, whereas sexual orientation is defined as a long-term pattern of emotional, romantic, or sexual attraction to other people. Hormones, particularly testosterone, have historically been implicated in sexual desire and attraction; however, emerging studies suggest that hormones primarily regulate desire, rather than patterns of sexual attraction.
This article discusses the biological mechanisms implicated in both sex drive and sexual orientation, how hormones influence these processes, and common misconceptions about human sexuality.
Hormones and sex drive
Testosterone is involved in sexual motivation and arousal; however, its effects on libido vary widely across individuals and contexts. Other hormones that modulate sexual interest include estrogen, which is involved in various aspects of sexual responsiveness, as well as prolactin and cortisol.2,3
Evidence from systematic reviews indicates that adult circulating hormone levels generally do not differ consistently according to sexual orientation. Although some studies have reported higher testosterone levels in lesbian and bisexual women, the overall literature is heterogeneous and often limited by small sample sizes and methodological differences.3
Several studies have not found consistent adult hormone differences sufficient to explain sexual orientation or other patterns of sexual attraction, supporting the view that hormones primarily regulate the intensity of sexual drive, rather than the target of that attraction. Overall, sexual desire reflects a dynamic interaction between hormonal state, physiology, and environmental context, whereas sexual orientation remains largely stable despite typical adult hormonal fluctuations.3
Researchers often distinguish between organizational and activational hormone effects. Organizational hormonal effects reflect how exposure to testosterone during prenatal development influences the structure and function of the brain. During this period, hormonal signals guide sexual differentiation in neural circuits that affect behavior, cognition, and attraction.1,2,4
In contrast, activational effects occur after puberty, when circulating hormones regulate the expression of behaviors without fundamentally altering brain organization. Adult hormone levels can affect libido, mood, and physiological reactions without affecting fundamental attributes like sexual orientation.2,4
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Hormones and sexual orientation
Current biological models propose that prenatal hormone exposure contributes to the development of sexual orientation by influencing sexual differentiation of the brain during critical developmental windows.1,2,4
Prenatal exposure to gonadal hormones or endocrine disruptors can alter brain development, with animal studies providing the strongest causal evidence and human studies mainly providing observational or natural-experiment evidence. Specifically, exposure to higher concentrations of testosterone during early development has been associated with greater attraction towards women, whereas lower embryonic exposure to androgenic signaling may be associated with attraction preferences towards men.
This evidence has primarily been obtained from studying human medical conditions like congenital adrenal hyperplasia in females, which is associated with increased exposure to androgens during prenatal development and non-heterosexual outcomes.
In contrast, XY individuals with complete androgen insensitivity syndrome (CAIS), a condition in which the body is unable to respond to androgen stimulation despite the presence of XY chromosomes, are typically raised as females and develop a female gender identity with predominant male-oriented attraction patterns, thus exemplifying the role of androgen signaling in sexual differentiation and development.
Other conditions, such as 5α-reductase deficiency, similarly demonstrate how altered hormonal function affecting androgen conversion and pubertal sexual differentiation may influence future sexual characteristics.1,2,4
Studies of individuals with congenital adrenal hyperplasia (CAH) provide some of the strongest evidence for prenatal hormonal influences on sexual orientation. Compared with unaffected women, women with CAH are more likely to report same-sex attraction or non-heterosexual identities, although substantial individual variation remains.1,2,4
Family, twin, and developmental studies additionally suggest that genetic factors contribute to sexual orientation. However, no single gene, hormone, or developmental pathway has been shown to determine sexual orientation on its own.1,4
Importantly, these findings relate to early developmental processes, rather than adult physiology. Available evidence does not support the idea that adult circulating steroid hormone levels can reliably explain or be altered to change sexual orientation.1,3,4
Brain structure and sexual orientation
Within the brain are sexually dimorphic regions, such as the hypothalamic nuclei and other areas involved in reproductive and social behavior. Recent evidence suggests that these neuroanatomical structures may differ in size, neuron count, and/or network density based on sexual orientation.
Other structural differences that have been observed in the brains of homosexual men include smaller thalamus volumes, as well as thinner right orbitofrontal and visual cortices, with no significant differences observed between heterosexual men and homosexual women within these brain regions.5
More recent voxel-based morphometry research has identified differences in gray matter volume within the thalamus, putamen, and precentral gyrus associated with sexual orientation. These effects were not identical in men and women, suggesting that the neuroanatomical correlates of sexual orientation may differ according to biological sex.5
Research also suggests that homosexual men exhibit more symmetrical cortex sizes as compared to heterosexual men, a feature that is similarly observed in heterosexual women.
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Although neuroimaging findings suggest that sexual orientation is associated with measurable differences in brain structure and connectivity, these studies cannot determine whether such differences are causes, consequences, or correlates of sexual orientation.5
Nevertheless, these studies are associated with numerous limitations, including heterogeneous study populations, small sample sizes, inconsistent replication across studies, and small differences. Thus, these observations do not establish causation, and evidence of biological contribution should not be interpreted as biological determinism.
Important considerations
To date, most research on potential associations between hormones and sexual orientation has been obtained from natural experiments or observational studies that infer causal links between pregnancy hormone levels and sexual orientation. These approaches provide valuable insights but are inherently limited by confounding factors and variability in study design.1,4
None of the biological factors identified so far is able to explain by itself the incidence of homosexuality in all individuals.2”
Current evidence supports a multifactorial model in which prenatal hormones, genetic influences, developmental processes, and environmental factors interact to shape sexual orientation.1,2,4
Another major challenge is attributed to the highly heterogeneous definition of sexual orientation, with available criteria like identity, behavior, and/or attraction that may not completely align with specific preferences, making it difficult to compare results across studies.
These limitations emphasize the need for interdisciplinary research to better understand the biological determinants of this highly complex aspect of human behavior.
References
- Rosenfield, K. A., Dawood, K., & Puts, D. A. (2018). Organizational effects of hormones on sexual orientation. In Routledge International Handbook of Social Neuroendocrinology (pp. 256-280). https://www.researchgate.net/publication/338925121_Organizational_effects_of_hormones_on_sexual_orientation
- Balthazart, J. (2011). Minireview: Hormones and human sexual orientation. Endocrinology 152(8); 2937-2947. DOI: 10.1210/en.2011-0277. https://academic.oup.com/endo/article-abstract/152/8/2937/2457178
- Harris, A., Bewley, S., & Meads, C. (2020). Sex hormone levels in lesbian, bisexual, and heterosexual women: Systematic review and exploratory meta-analysis. Archives of Sexual Behavior 49(7); 2405-2420. DOI: 10.1007/s10508-020-01717-8. https://link.springer.com/article/10.1007/s10508-020-01717-8
- Roselli, C. E. (2018). Neurobiology of gender identity and sexual orientation. Journal of Neuroendocrinology 30(7). DOI: 10.1111/jne.12562. https://onlinelibrary.wiley.com/doi/10.1111/jne.12562
- Votinov, M., Goerlich, K. S., Puiu, A. A., et al. (2021). Brain structure changes associated with sexual orientation. Scientific Reports 11 5078. DOI: 10.1038/s41598-021-84496-z. https://www.nature.com/articles/s41598-021-84496-z
Further Reading
Last Updated: Jun 3, 2026