Testosterone

Testosterone is the body's main male sex hormone, driving muscle mass, libido, energy, and male sexual development. It's a steroid hormone, not a peptide. It's FDA-approved as a prescription drug for male hypogonadism (low testosterone), available as injectable esters such as cypionate and enanthate, gels, pellets, oral capsules, and a nasal spray. In the US it's a DEA Schedule III controlled substance, so it's legal only with a prescription. It's included here because it's often used alongside peptide protocols.

Testosterone replacement therapy treats men with confirmed low testosterone plus symptoms, and it's FDA-approved for that use. Large trials and Endocrine Society guidelines support replacement in that group: the TTrials showed benefits on several measures, and the TRAVERSE trial found no increase in major cardiac events versus placebo in middle-aged and older men with hypogonadism. Those safety findings come from replacement-dose contexts and do not extend to the much higher supraphysiologic doses used outside medical care.

DEA Schedule III controlled substance under the US Controlled Substances Act (per the Anabolic Steroid Control Act of 1990, expanded by the Anabolic Steroid Control Act of 2004 and the Designer Anabolic Steroid Control Act of 2014 — DASCA). Prescription required for legal use in the US; off-prescription or research-community supply outside an authorized prescriber relationship is illegal under federal law. FDA-approved for treatment of male hypogonadism (primary or hypogonadotropic) under multiple branded and generic NDAs across multiple ester forms and delivery routes (intramuscular, subcutaneous, transdermal, oral, pellet implant, nasal). WADA-banned in regulated sport — explicitly listed under Section S1.1 (Anabolic Androgenic Steroids) of the 2026 Prohibited List, the strongest WADA prohibition tier.

Testosterone is a DEA Schedule III controlled substance requiring a prescription, and use outside a prescribed relationship is illegal under US federal law; it is banned in WADA-tested sport, and treatment requires lab monitoring (for example of red-blood-cell count and estradiol). VialWise is a research and educational reference, not medical advice — consult a licensed professional.

⚠️ For research and educational purposes only. Testosterone is a DEA Schedule III controlled substance and is FDA-approved as a prescription drug for male hypogonadism. Information in this entry is informational, not medical advice. Always confirm dose calculations with the in-app calculator and consult appropriate professional guidance before any protocol decisions. Use of testosterone outside a prescribed therapeutic relationship is illegal under US federal law and carries criminal as well as health-related consequences.

⚠️ Testosterone is not a peptide. This entry exists in the Vialwise library because researchers running peptide protocols frequently use TRT (testosterone replacement therapy) or research-community testosterone alongside peptide stacks (CJC-1295/Ipamorelin, BPC-157/TB-500, AOD-9604, GLP-1 agonists). The compound is a 19-carbon steroid hormone, not a peptide — produced naturally in the testes (and adrenals/ovaries) and synthesized commercially in multiple ester forms. Mechanistically, pharmacologically, and regulatorily it sits in a different category from the rest of the Vialwise library. Researchers should be explicit with themselves about which compound class they are using and the corresponding regulatory and safety considerations.

⚠️ DEA Schedule III. Prescription required. Testosterone has been a Schedule III controlled substance under the US Controlled Substances Act since the Anabolic Steroid Control Act of 1990.[⁸] The schedule was expanded by the Anabolic Steroid Control Act of 2004 (effective January 20, 2005 — eliminated the prior "muscle growth" requirement and added 59 specific substances) and by the Designer Anabolic Steroid Control Act of 2014 (DASCA) (closing the chemical-modification loophole for designer derivatives). Possessing, distributing, or using testosterone outside an authorized prescriber relationship is a federal criminal offense in the US, distinct from the regulatory environment of unapproved peptides like BPC-157 or TB-500. State laws also apply; some states have additional restrictions. Researchers in jurisdictions outside the US face different regulatory environments.

⚠️ Multiple ester forms with substantially different pharmacokinetics. Do not confuse them. Testosterone is sold in multiple ester forms with substantially different half-lives, peak/trough profiles, dosing intervals, and delivery routes. The most common are: - Testosterone cypionate (Depo-Testosterone) — IM oil-based injection, half-life ~8 days, typical TRT dose weekly - Testosterone enanthate — IM oil-based injection (and subcutaneous via Xyosted autoinjector), half-life ~4.5 days, typical TRT dose weekly ( starting for SC enanthate via Xyosted) - Testosterone propionate — IM oil-based injection, half-life ~0.8 days (~20 hours), requires more frequent dosing (every 1–3 days) — uncommon in modern TRT but encountered in research-community use - Testosterone undecanoate — IM (Aveed, dosed every 10 weeks after loading) and oral (Jatenzo, Tlando), much longer half-life - Testosterone suspension — water-based, no ester, very short acting; primarily research/legacy use - Transdermal gel/cream (AndroGel 1.62%, Testim, Vogelxo, compounded creams) — daily application, different absorption profile - Subcutaneous pellet (Testopel) — implanted every 3–6 months - Mixed-ester products (Sustanon 250) — combinations of propionate, phenylpropionate, isocaproate, decanoate; not FDA-approved in the US but encountered in research/international contexts The dosing patterns, delivery routes, and pharmacokinetic profiles for each ester are not interchangeable. Researchers should be explicit with themselves about which ester they are using, in what formulation, by what route, and at what dose interval. This entry treats each ester as a related but distinct preparation and flags inline where dosing claims apply to one ester vs another.

⚠️ TRT (replacement) vs supraphysiologic / research-community use are pharmacologically and regulatorily distinct. The published RCT efficacy and safety data for testosterone (Bhasin 2018 Endocrine Society guidelines,[¹] TTrials,[²] TRAVERSE[³]) is overwhelmingly from TRT contexts — adult men with documented hypogonadism (low total testosterone confirmed on multiple morning measurements, plus consistent symptoms), receiving doses titrated to mid-normal physiologic range (~400–700 ng/dL trough). Research-community supraphysiologic use — doses targeting peaks of 1500–3000+ ng/dL — operates outside the published RCT evidence base for both efficacy and safety, and is also outside any FDA-approved indication, prescribing label, or DEA Schedule III prescription authority. The TRAVERSE cardiovascular-safety conclusions in particular ("non-inferiority to placebo on MACE in middle-aged and older men with hypogonadism")[³] do not generalize to the supraphysiologic-dose research-community use pattern. Researchers should be explicit with themselves about which dose context applies and what evidence base supports their specific use.

Testosterone is the principal endogenous androgen in humans, produced primarily by Leydig cells in the testes (with smaller contributions from the adrenal cortex and, in females, the ovaries). It is a 19-carbon steroid hormone, not a peptide — it is included in this library because researchers running peptide protocols frequently use testosterone alongside peptide stacks. Synthetic testosterone for therapeutic and research use is most commonly produced as an ester (a fatty-acid chain attached to the 17β-hydroxyl group) which slows release from oil depot injections; the unmodified molecule has a very short systemic half-life (minutes), which is why most preparations use ester forms.

Endogenous role. Testosterone is essential for male sexual development, fertility, muscle and bone maintenance, erythropoiesis (red blood cell production), libido and sexual function, and broader metabolic and CNS effects. Endogenous serum levels in healthy adult men typically range 300–1000 ng/dL (with diurnal variation — morning peak is highest). Levels decline gradually with age (~1% per year after age 30 in many men), but pathologic hypogonadism (consistently low T plus symptoms) is distinct from age-related decline. The Bhasin 2018 Endocrine Society guidelines define hypogonadism as "symptoms and signs consistent with testosterone deficiency and unequivocally and consistently low serum testosterone concentrations" — both clinical and laboratory criteria are required.[¹]

Regulatory status (US). Testosterone has been a DEA Schedule III controlled substance under the US Controlled Substances Act since the Anabolic Steroid Control Act of 1990. The legal definition of "anabolic steroid" was expanded by the Anabolic Steroid Control Act of 2004 (effective January 20, 2005) and the Designer Anabolic Steroid Control Act of 2014 (DASCA).[⁸] Testosterone is FDA-approved for treatment of male hypogonadism (primary or hypogonadotropic, congenital or acquired) under multiple NDAs spanning multiple ester forms and delivery routes — Depo-Testosterone (cypionate IM, ANDA 085635, since the 1950s), Xyosted (enanthate SC autoinjector, NDA 209863, approved 2018), AndroGel (transdermal 1% and 1.62%), Testim, Vogelxo, Aveed (undecanoate IM, every-10-weeks dosing), Jatenzo and Tlando (oral undecanoate), Natesto (intranasal), Testopel (subcutaneous pellet), among others. Each branded product has its own FDA-approved indication, dosing, and labeling — they are not interchangeable.[⁵][⁶]

Regulatory status (sport — WADA). Testosterone is explicitly listed in Section S1.1 (Anabolic Androgenic Steroids) of the 2026 WADA Prohibited List, the strongest WADA prohibition tier. This is a fundamentally different prohibition category from the peptides covered elsewhere in this library (which sit in S2 under Peptide Hormones, Growth Factors, Related Substances, and Mimetics). Testosterone is prohibited at all times — in-competition and out-of-competition — for all athletes under WADA jurisdiction.[⁷] The catch-all clause in S1.1 also covers "other substances with a similar chemical structure or similar biological effect(s)" — closing the loophole for novel anabolic-steroid analogues.

Common research interests. Testosterone is one of the most widely used research peptides — although it is not technically a peptide. The most common contexts: - TRT (testosterone replacement therapy) — adult men with diagnosed hypogonadism. This is the FDA-approved use case and the use case supported by the largest body of RCT evidence.[¹][²][³] - Performance / research-community supraphysiologic use — outside FDA approval, outside DEA prescription authority, and outside the published RCT efficacy/safety data; widely encountered in athletic and bodybuilding contexts. Typically targets supraphysiologic peak T (1500+ ng/dL) over multi-week or multi-month cycles. - Transgender masculinization (gender-affirming hormone therapy) — adult and adolescent transmasculine populations; FDA-off-label but widely practiced under specialist supervision; dose ranges typically overlap with TRT. - Anti-aging / "men's health" clinic use — a controversial use case where TRT is prescribed in older men based on age-related decline rather than diagnostic criteria meeting the Endocrine Society's definition of hypogonadism. The Bhasin 2018 guidelines explicitly recommend against routine TRT in men with age-related decline alone, in the absence of consistent symptoms and unequivocally low serum testosterone.[¹]

Stacking with peptide protocols (the reason this entry exists in Vialwise). Researchers using peptide stacks frequently combine testosterone with one or more of: GH-secretagogue blends (CJC-1295/Ipamorelin), regenerative peptides (BPC-157, TB-500), GLP-1 / GIP / glucagon agonists (semaglutide, tirzepatide, retatrutide) for body-composition cycles, and AOD-9604 for additional fat loss. Each of these stack pairings has its own rationale and risk profile (see the relevant entries' Stacks sections for details).

Commonly reported

• Erythrocytosis / elevated hematocrit — most common dose-limiting side effect; monitor hematocrit at 3 months and 6 months. If >54%, hold therapy. SC enanthate produces lower hematocrit elevation than IM cypionate at the same dose.[⁴]
• Increased blood pressure — FDA added a class-wide warning in 2025 that testosterone can raise blood pressure, after required post-market ambulatory blood-pressure monitoring (ABPM) studies showed a blood-pressure increase across all testosterone routes. Blood pressure should be monitored during therapy.[⁹]
• Acne, oily skin, increased body/facial hair — dose-related; typically more prominent with supraphysiologic doses
• Estradiol elevation — testosterone is aromatized to estradiol; mild elevation is normal and beneficial in most men, but symptomatic hyperestrogenism (gynecomastia, water retention, mood changes) is dose-dependent
• Suppressed endogenous testosterone production / testicular atrophy — exogenous testosterone suppresses LH and FSH via negative feedback, leading to reduced endogenous T production and reduced testicular size. Reversible after discontinuation in most men but recovery can take months.
• Reduced fertility / sperm production — hypothalamic-pituitary-testicular axis suppression reduces spermatogenesis. TRT is not recommended for men actively trying to conceive. The Bhasin 2018 guidelines specifically address this.[¹]
• Mood and behavioral changes — variable. Some men report improved mood and energy on TRT (TTrials reported small mood improvements);[²] others report irritability, particularly at supraphysiologic doses or with rapid level fluctuations.
• Site reactions — IM injection site pain or swelling; SC injection site reactions; transdermal gel skin irritation; pellet implant site reactions.
• Acute changes around injection — for IM ester injections, some men report a "pre-injection low" before re-dosing as serum levels drop near trough.

Serious

• Severe acute chest pain, shortness of breath, leg swelling — possible pulmonary embolism (TRAVERSE reported elevated PE rate in the TRT group)[³]
• Acute palpitations, irregular heartbeat — possible atrial fibrillation (TRAVERSE reported elevated AF rate in the TRT group)[³]
• Sudden severe headache, vision changes, weakness — possible stroke
• Acute abdominal pain, decreased urine output — possible acute kidney injury (TRAVERSE reported elevated AKI rate)[³]
• Unexplained leg swelling, redness, pain — possible deep vein thrombosis
• Severe psychiatric changes (mania, severe aggression, psychosis) — particularly with supraphysiologic doses
• Hematocrit >54% with symptoms (headache, dizziness, blurred vision)
• New-onset erectile dysfunction or worsening BPH symptoms

Known or suspected prostate cancer or breast cancer in men — testosterone can drive growth of androgen-sensitive cancers

Untreated severe sleep apnea — testosterone can worsen sleep apnea; should be managed before initiating TRT

Severe cardiac, hepatic, or renal disease — exercise caution; balance against established benefit

Pregnancy (testosterone can virilize a female fetus)

Active fertility goals — TRT suppresses spermatogenesis; should not be used in men actively trying to conceive

Hematocrit >54% — start ineligible until hematocrit is managed; therapy should be held if hematocrit reaches this threshold during treatment

Recent (within 6 months) cardiovascular event — caution; TRT initiation should typically be delayed and balanced against other clinical needs

Pediatric use — generally contraindicated outside specialist settings; testosterone can prematurely close growth plates and disrupt normal pubertal development

Active breast cancer (in women) — even off-label transgender use should be reconsidered in this context

Pregnancy and lactation: contraindicated — virilization risk to fetus; testosterone is excreted in milk.

Concurrent use of warfarin and other anticoagulants — testosterone can potentiate warfarin effects; monitor INR closely.

Concurrent use of insulin or oral hypoglycemics — testosterone can affect glucose metabolism; monitor glucose carefully when initiating or adjusting TRT.

Increased blood pressure (FDA class-wide warning, 2025). FDA added a class-wide warning that testosterone can increase blood pressure — confirmed across all routes by required post-market ambulatory blood-pressure monitoring (ABPM) studies. Blood pressure should be monitored during therapy, and the increase should be weighed in individuals with hypertension or cardiovascular risk.[⁹]

Cardiovascular boxed-warning removal (FDA, 2/28/2025). Following the TRAVERSE cardiovascular-safety results,[³] FDA issued class-wide testosterone labeling changes that removed the prior boxed warning on increased cardiovascular risk and added the TRAVERSE results to all testosterone product labels, while retaining the "Limitation of Use" language for age-related hypogonadism.[⁹] This reflects the current FDA regulatory posture for TRT-range use and does not extend to supraphysiologic-dose research-community use.

Regulatory note (US): Testosterone is a DEA Schedule III controlled substance — possessing, distributing, or using testosterone outside an authorized prescriber relationship is a federal criminal offense.[⁸]

Regulatory note (sport): Testosterone is explicitly listed in WADA 2026 Prohibited List Section S1.1 (Anabolic Androgenic Steroids), prohibited at all times.[⁷] Researchers competing in any WADA-tested sport will test positive on standard testing protocols.

Transgender hormone therapy contexts: TRT for masculinization in transmasculine populations is widespread but technically off-label; specialist supervision (endocrinology, primary care with experience, or gender-affirming clinic) is the standard of care.

Androgen

A male sex hormone (such as testosterone) that supports male sexual development and traits like muscle and bone maintenance.

Controlled substance

A drug regulated by the government (in the US, scheduled by the DEA) because of its potential for misuse; requires a prescription for legal use.

Testosterone replacement therapy (TRT)

Medically supervised use of testosterone to treat men with diagnosed low testosterone.

Estradiol

The main form of estrogen; relevant in men because some testosterone is converted to estradiol.

1. Bhasin S, Brito JP, Cunningham GR, Hayes FJ, Hodis HN, Matsumoto AM, Snyder PJ, Swerdloff RS, Wu FC, Yialamas MA. (2018). Testosterone Therapy in Men With Hypogonadism: An Endocrine Society Clinical Practice Guideline. The Journal of Clinical Endocrinology & Metabolism, 103(5):1715–1744.(PMID 29562364)
2. Snyder PJ, Bhasin S, Cunningham GR, Matsumoto AM, Stephens-Shields AJ, Cauley JA, Gill TM, Barrett-Connor E, Swerdloff RS, Wang C, Ensrud KE, Lewis CE, Farrar JT, Cella D, Rosen RC, Pahor M, Crandall JP, Molitch ME, Cifelli D, Dougar D, Fluharty L, Resnick SM, Storer TW, Anton S, Basaria S, Diem SJ, Hou X, Mohler ER 3rd, Parsons JK, Wenger NK, Zeldow B, Landis JR, Ellenberg SS; Testosterone Trials Investigators. (2016). Effects of Testosterone Treatment in Older Men. The New England Journal of Medicine, 374(7):611–624.(PMID 26886521 · NCT00799617)
3. Lincoff AM, Bhasin S, Flevaris P, Mitchell LM, Basaria S, Boden WE, Cunningham GR, Granger CB, Khera M, Thompson IM Jr, Wang Q, Wolski K, Davey D, Kalahasti V, Khan N, Miller MG, Snabes MC, Chan A, Dubcenco E, Li X, Yi T, Huang B, Pencina KM, Travison TG, Nissen SE; TRAVERSE Study Investigators. (2023). Cardiovascular Safety of Testosterone-Replacement Therapy. The New England Journal of Medicine, 389(2):107–117.(PMID 37326322)
4. Choi EJ, Xu P, Barham D, El-Khatib FM, Yafi FA, Kavoussi PK. (2022). Comparison of Outcomes for Hypogonadal Men Treated With Intramuscular Testosterone Cypionate Versus Subcutaneous Testosterone Enanthate. The Journal of Urology, 207(3):677–683.(PMID 34694927)
5. Pfizer / Pharmacia & Upjohn Company. Depo-Testosterone (testosterone cypionate) Injection prescribing information. US Food and Drug Administration. ANDA 085635 (originally approved 1953; label revised 2025 to reflect the FDA class-wide testosterone labeling changes — see [9]).
6. Antares Pharma / Halozyme Therapeutics. Xyosted (testosterone enanthate) injection prescribing information. US Food and Drug Administration. NDA 209863, approved September 2018; current label SUPPL-020 (2025).
7. World Anti-Doping Agency. The 2026 Prohibited List, International Standard (effective 1 January 2026). Canonical PDF: wada-ama.org/sites/default/files/2025-09/2026list_en_final_clean_september_2025.pdf (linked from the WADA landing page at wada-ama.org/en/prohibited-list; local archival copy in `docs/legal/wada-2026-prohibited-list.pdf`). Testosterone is named explicitly under Section S1.1 (Anabolic Androgenic Steroids) — not S2 like the peptides covered elsewhere in this library. Verbatim from the canonical PDF, page 5, alphabetic listing under S1.1 anabolic androgenic steroids (AAS): "Testosterone" — listed alongside other named anabolic-androgenic steroids (Bolasterone, Boldenone, Stanozolol, Trenbolone, etc.). The S1.1 catch-all clause reads: "and other substances with a similar chemical structure or similar biological effect(s)" — the strongest WADA prohibition tier. Prohibited at all times, in-competition and out-of-competition.
8. US Drug Enforcement Administration. Anabolic Steroids — Schedule III Controlled Substances under the Anabolic Steroid Control Act of 1990 (Pub. L. No. 101-647), the Anabolic Steroid Control Act of 2004 (Pub. L. No. 108-358), and the Designer Anabolic Steroid Control Act of 2014 (Pub. L. No. 113-260; "DASCA"). DEA Diversion Control Division reference: deadiversion.usdoj.gov/drug_chem_info/anabolic.pdf. Federal Register implementation notice for the 2004 Act: federalregister.gov/documents/2005/12/16/05-23907/implementation-of-the-anabolic-steroid-control-act-of-2004. The regulatory chain that places testosterone under DEA Schedule III in the US: the 1990 Act placed anabolic steroids (defined to include testosterone and "any drug or hormonal substance, chemically and pharmacologically related to testosterone... that promotes muscle growth") into Schedule III; the 2004 Act expanded the definition (eliminated the "muscle growth" requirement, added 59 specifically named substances); the 2014 DASCA closed the chemical-modification loophole for designer derivatives.

• CJC-1295 / Ipamorelin Blend — discussed together in this entry's stacks section
• BPC-157 / TB-500 Blend — discussed together in this entry's stacks section
• AOD-9604 — discussed together in this entry's stacks section