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Last reviewed: May 12, 2026 Last updated: May 12, 2026

Written by: Jay Hastings , CEO of PlexusDx

Jay Hastings is the CEO of PlexusDx, a precision health company focused on genetic testing, blood biomarker insights, and personalized wellness recommendations. He has more than 20 years of experience across healthcare innovation, genomics, laboratory operations, healthcare investing, and strategic finance. His work has included scaling healthcare startups, leading CLIA lab integrations, and helping expand consumer access to precision health tools.

Medically reviewed by: Jayden Lee, PharmD, EMBA

Jayden Lee, PharmD, EMBA, is the PlexusDx Medical Science Liaison with a PharmD and MBA specializing in pharmacogenomics and clinical product development, with a proven ability to bridge the gap between genomic research and practical patient outcomes. Dr. Lee has more than 10 years of professional experience in clinical pharmacy, academia, and research.

This article is part of the PlexusDx Education Hub — your resource for evidence-based guidance on hormones and fertility. Browse all Hormones & Fertility education

Testosterone gets most of the attention in the androgen conversation. But for many of the functions men most associate with androgen action — prostate tissue response, scalp hair follicle sensitivity, and certain aspects of body composition — the active molecule isn't testosterone at all. It's DHT, dihydrotestosterone, produced from testosterone through a single enzymatic conversion controlled by SRD5A2, the gene encoding the type 2 isoform of 5-alpha reductase. How much DHT your body makes from any given testosterone level is genetically set by your SRD5A2 variants before any protocol, supplement, or lifestyle change enters the picture.

What Is SRD5A2 and What Does 5-Alpha Reductase Do?

SRD5A2 encodes the type 2 isoform of 5-alpha reductase — a steroid-metabolizing enzyme expressed predominantly in the prostate, skin, scalp hair follicles, and seminal vesicles. Its biochemical function: catalyze the irreversible conversion of testosterone into 5-alpha-dihydrotestosterone (DHT). That conversion matters because DHT binds the androgen receptor with approximately two to three times the affinity of testosterone, and it dissociates more slowly — making it a significantly more potent androgen signal at the same receptor governed by AR CAG repeat length.

The implication is direct: the total androgen effect in any DHT-sensitive tissue is determined not just by circulating testosterone levels or receptor sensitivity, but by how efficiently local enzyme machinery converts testosterone substrate into DHT. SRD5A2 variants that alter that conversion rate change the potency of the androgen signal reaching those tissues — independently of serum testosterone measurements.

The PlexusDx Precision Peptide Genetic Test analyzes SRD5A2 as part of 14 pathways, 49 peptides, and 150+ genetic insights — placing DHT-pathway genetics within the Reproductive Health pathway alongside the five other gene variants that complete the male hormone picture.

How SRD5A2 Variants Shape DHT Production

SRD5A2 carries several well-characterized variants with documented functional effects on enzyme activity. Among the most studied are Val89Leu (rs523349) and Ala49Thr — common polymorphisms with real-world frequency across populations and peer-reviewed functional documentation. Val89Leu is associated with reduced 5-alpha reductase activity in certain contexts; Ala49Thr is associated with increased activity and higher DHT output from equivalent testosterone substrate.

These variants don't operate like switches. They shift enzyme efficiency along a spectrum, and a man's genotype places him at a point on that spectrum that is stable across his lifetime. A man with higher-activity SRD5A2 converts a greater fraction of available testosterone into DHT, producing a more potent androgen signal at DHT-sensitive receptors. A man with lower-activity variants converts proportionally less — keeping more testosterone in unconverted form but delivering a weaker DHT signal to the tissues that depend on it.

Why DHT Is Not Simply Stronger Testosterone

DHT has a distinct tissue distribution and functional profile that makes it qualitatively different from testosterone, not just quantitatively more potent. Understanding where SRD5A2 activity matters most:

Prostate tissue: DHT is the primary androgen driver of prostate cellular signaling. 5-alpha reductase type 2 is highly expressed in prostate tissue, and local DHT concentration — shaped substantially by SRD5A2 activity — is a central variable in prostate androgen biology.

Scalp hair follicles: Follicle sensitivity to androgens is primarily DHT-mediated. SRD5A2 variants influence the DHT signal reaching scalp follicles, making them relevant to understanding genetic predisposition to androgen-related hair changes in the context of any androgen-pathway protocol.

Body composition and libido: Some aspects of androgen-related muscle tone, fat distribution, and sexual drive have DHT-dependent components that testosterone alone doesn't fully account for. SRD5A2 activity shapes how well those DHT-dependent pathways are fueled.

Androgen-pathway protocols: When androgen levels are elevated through any pathway support strategy, a man with high-activity SRD5A2 will produce more DHT from that elevated testosterone substrate than a man with lower-activity variants. Same protocol input, different DHT output — which a provider not accounting for SRD5A2 genetics cannot anticipate from bloodwork alone.

SRD5A2 in the Men's Hormone Gene Network

SRD5A2 is one of 6 Reproductive Health insights the Precision Peptide Genetic Test analyzes as a connected system — part of the broader framework in the Complete Guide to Genetic Men's Hormone Testing:

SHBG — sex hormone binding globulin variants govern how much free testosterone circulates as substrate for 5-alpha reductase to act on. High SHBG reduces available testosterone regardless of SRD5A2 activity — a supply constraint that sits upstream of the conversion step. SHBG Genetics: Why Your Free Testosterone Varies covers this interaction in detail.

CYP19A1 — aromatase and 5-alpha reductase compete for the same free testosterone substrate, routing it toward estradiol (CYP19A1) or DHT (SRD5A2) respectively. The relative activity of these two enzymes is one of the most important genetic variables shaping a man's androgen-estrogen-DHT balance. CYP19A1 and Estrogen Conversion in Men covers aromatase genetics in full.

AR (CAG repeats) — androgen receptor sensitivity determines how the DHT that SRD5A2 produces is read at the cellular level. High-activity SRD5A2 paired with short AR CAG repeats creates a potent androgen signaling environment. Lower enzyme activity paired with longer repeats produces a significantly more muted one. Androgen Receptor CAG Repeats: Sensitivity Explained covers the receptor dimension in detail.

ESR1 and ESR2 — estrogen receptor variants determine tissue sensitivity to estradiol, the competing downstream product of CYP19A1 activity. The DHT-to-estradiol ratio — jointly shaped by SRD5A2 and CYP19A1 — is a key variable in hormonal balance, and receptor sensitivity genetics determine how that ratio is experienced in practice.

Together, these 6 insights map the genetic architecture of male hormone signaling from supply through enzymatic conversion to receptor-level response. SRD5A2 is the DHT production node — the enzymatic conversion step that determines which androgen signal tissues actually receive.

What Your SRD5A2 Results Can and Cannot Tell You

SRD5A2 results reveal your genetic baseline for 5-alpha reductase activity — the enzymatic capacity your body brings to the conversion of testosterone into DHT. They are not a measurement of your current DHT level; that requires blood testing. They do not diagnose any condition. And they do not predict your response to any specific androgen-pathway compound or protocol.

What they deliver is a defined genetic variable: how aggressively your DHT production pathway operates from a given testosterone substrate, which informs how providers interpret androgen-sensitive outcomes and monitor protocols across time. Genetics as a guide, not a guarantee — and as one of 6 Reproductive Health insights within 14 total pathways and 150+ genetic insights, SRD5A2 is a precision input to a clinical picture no single blood panel can complete on its own.

The Precision Peptide Genetic Test analyzes how your genes influence hormone-related biological pathways. It does not recommend, prescribe, or determine which peptides you should use. Consult a qualified healthcare provider before beginning any peptide protocol.

Ready to understand your DHT conversion genetics and where SRD5A2 fits in your hormone profile? Take the Precision Peptide Genetic Test

Frequently Asked Questions About SRD5A2 and 5-Alpha Reductase Genetics

What does SRD5A2 measure in the Precision Peptide Genetic Test?

SRD5A2 variants reveal your genetic baseline for 5-alpha reductase activity — the rate at which your body converts testosterone to DHT. The Precision Peptide Genetic Test analyzes SRD5A2 as one of 6 Reproductive Health insights within 14 total pathways and 150+ genetic insights. Results reflect conversion tendency, not a current DHT measurement.

Why does DHT matter more than testosterone in some androgen contexts?

DHT binds the androgen receptor with approximately 2–3 times the affinity of testosterone and dissociates more slowly — producing a more potent androgen signal. Prostate tissue, scalp hair follicles, and certain body composition pathways are primarily DHT-dependent. SRD5A2 variants determine how much DHT your body produces from available testosterone in those contexts.

How does SRD5A2 interact with CYP19A1 and AR in the men's hormone panel?

SRD5A2 and CYP19A1 compete for the same testosterone substrate — routing it toward DHT or estradiol. AR CAG repeats determine how sensitively tissues respond to the DHT produced. SHBG governs the free testosterone available to both enzymes. The Precision Peptide Genetic Test analyzes all 6 Reproductive Health insights together for a complete picture.

This article is part of the PlexusDx Education Hub. Browse all Hormones & Fertility education

Medical and Editorial Standards

Medical review process: This article was reviewed for medical accuracy, scientific clarity, evidence alignment, and appropriate discussion of genetics, medications, supplements, biomarkers, and health-related claims.

Sources and evidence: PlexusDx educational content is developed using peer-reviewed research, clinical literature, reputable medical references, and, where applicable, public health or regulatory guidance. References are included at the end of the article when scientific, medical, or health-related claims are discussed.

Commercial transparency: PlexusDx offers genetic testing, blood biomarker testing, personalized supplement recommendations, and related precision wellness services. Product mentions are intended to help readers understand available options and should not be interpreted as medical advice.

Important disclaimer: PlexusDx educational content is for informational purposes only and should not be used as a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider before making decisions about medications, supplements, genetic testing, lab testing, or health-related care.