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Muscle & performance

Testosterone Decanoate

Testosterone with the long decanoate ester, as a single ester at 300 mg/ml, for infrequent injections and steady levels.

3 min read 8 sources

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Glass vial with golden oil and a black TPD label next to a blue 3D steroid molecule with a long ester chain, symbolic image for Testosterone Decanoate
Approved in a blend · not as a single ester

Summary

At a glance

Sources checked on 26 Oct 2026

No sperm after 12 weeks
80 %

20 men, together with a progestin implant, all below 1 million per ml1

Haematocrit
+15 %

In the same study, haemoglobin rose by 9 percent1

Phase IIb study
48 weeks

55 and 57 men, injection every 4 or 6 weeks, with 4 weeks trough levels in the normal range2

Phase 3 in the registry
1 trial

only with the four-ester blend, none as a single ester, as of 26 Oct 20267

  • Testosterone Decanoate is testosterone with a ten-carbon decanoate ester. In the body the ester is split off and testosterone remains, acting on the androgen receptor.84
  • Decanoate has mainly been studied in male contraception research. With an injection every four weeks trough levels rose with each injection and the peak briefly went above the normal range.1
  • LH and FSH fell quickly, together with a progestin 80 percent had no sperm after 12 weeks. After stopping, sperm and gonadotropins recovered.12
  • Haemoglobin rose by 9 and haematocrit by 15 percent. One study was stopped early because some men had rising liver values.1
  • Decanoate is not approved as a single ester, but as the longest part of a four-ester testosterone blend it has been approved in the UK since 1973. Everything here is the state of research, not a recommendation.6
Profile

Updated October 2026

Class
Testosterone ester

long-acting, anabolic steroid

Form
Oil

300 mg/ml

Use
Intramuscular

1-2x per week

Half-life
long

longer than enanthate

WADA
Banned

S1, anabolic agents

Sizes
2 sizes

300mg/ml, 500mg/ml

Contents 15 sections
  1. At a glance
  2. What is Testosterone Decanoate?
  3. How it works
  4. Use and dosing
  5. Injection
  6. What the research shows
  7. Research status
  8. Side effects
  9. Practice
  10. Storage
  11. PCT / after coming off
  12. Related compounds
  13. FAQ
  14. Glossary
  15. Sources

What is Testosterone Decanoate?

Testosterone Decanoate is testosterone with a ten-carbon decanoate ester attached. The long ester makes the molecule very fat-soluble, so it stays in the oil depot for a long time and enters the blood slowly. Decanoate is best known as the long component of ester blends such as Sustanon; here it comes as a single ester at 300 mg/ml.

In the body the ester is cleaved off and plain testosterone remains. The effect is no different from enanthate, only the release is slower and steadier.

This information is for research and educational purposes only. No medical advice.

Comparison

Short and long esters

The same compound at the same receptor with esters of different length, as stated in the TPD lexicon. Tap a card to open its entry.

Short ester Testosterone Propionate AR Medium ester Testosterone Phenylpropionate AR Long ester Testosterone Enanthate AR Long ester Testosterone Cypionate AR
Very long ester Testosterone Decanoate AR
Ultra-long ester Testosterone Undecanoate AR

How it works

Testosterone binds the androgen receptor in muscle, bone and many other tissues. Studies show dose-dependent gains in fat-free mass, muscle cross-section and strength, along with more nitrogen retention and stronger red blood cell production.

Part of it is converted to estradiol by aromatase and part to DHT by 5-alpha reductase. That is why estrogen issues and androgenic effects such as acne come with every testosterone ester. The decanoate ester has no effect of its own; it only sets how fast testosterone leaves the depot.

Where it acts

One receptor, several organs

Tap a point or a card. Grey = effect seen in trials.

  1. Hypothalamus and pituitary

    LH and FSH fell quickly and kept falling1

    Observed in trials
  2. Testes

    Sperm production suppressed, recovered after stopping2

    Observed in trials
  3. Blood

    Haemoglobin +9 percent, haematocrit +15 percent1

    Observed in trials
  4. Liver

    Raised liver values in some men, study stopped early1

    Observed in trials
  5. Skeletal muscle

    Fat-free mass rose with the testosterone level, study with enanthate5

    Observed in trials

Targets in the ChEMBL database8

Compound CHEMBL386630: one recorded mechanism, Testosterone once the ester is split off: agonist, direct binding.

Androgen receptor
Gene
AR
UniProt
P10275
ChEMBL
CHEMBL1871
Action
Testosterone once the ester is split off: agonist, direct binding
Blue 3D molecules slowly leave an oil droplet and reach bright muscle fibres, symbolic image
The long ester releases testosterone only slowly from the depot. Symbolic image.

Use and dosing

Dosing

Dosing, titration and syringe

Loading the dosing information …

  • Getting started and stepping up, drawn as a staircase
  • Units on the U-100 syringe for every step
  • How long one vial lasts
Glass vial with golden oil and a black TPD label, a disposable syringe in front, symbolic image
Long ester: one to two doses per week are enough. Symbolic image.

Injection

The oil is ready to use and is not mixed. The usual route is intramuscular into the glute, thigh or shoulder; disinfect the site first and rotate sites regularly.

  • Thicker needle to draw, thinner needle to inject.
  • Subcutaneous works for small volumes, at most about 0.5 ml per site, injected slowly.
  • Small lumps after subcutaneous shots are common and usually fade within a few days.

What the research shows

Decanoate has mainly been studied in male hormonal contraception. Anderson and colleagues (Contraception, 2002) gave 400mg every four weeks together with etonogestrel: trough levels rose with each injection, LH and FSH fell quickly, hemoglobin went up 9 percent and hematocrit 15 percent.

The larger phase IIb trial by Hay and colleagues (JCEM, 2005) compared four- and six-week intervals over 48 weeks. With four weeks, trough levels sat in the normal range. After stopping, sperm counts and gonadotropins recovered in both groups.

A doping control study with an ester mix showed that detection time in blood depends on the ester, with the long esters lasting longest. Kicman (Br J Pharmacol, 2008) summarizes the general pharmacology of esterification.

Study results

What the trials measured

Interactive: switch tabs, tap points, show or hide arms. Arms are named relative to each other, no dosing advice.

Suppressed sperm production after 12 weeks1

Share of the 20 men, injection every 4 weeks plus progestin implant

At most 1 million per ml1
Decanoate with progestin implant 100%
No detectable sperm1
Decanoate with progestin implant 80%

In the larger phase IIb study all men but one were below 1 million per ml after 48 weeks. After stopping, sperm counts and gonadotropins recovered in both groups. Research data, not a contraceptive.

Rise in red blood values1

Change in percent, 20 men, injection every 4 weeks plus progestin implant

Haemoglobin1
Decanoate with progestin implant +9%
Haematocrit1
Decanoate with progestin implant +15%

Body weight rose too. The study was stopped after 12 to 18 weeks because some men had raised liver values.

Fat-free mass after 20 weeks5

Gain in kg in the three higher of five dose levels, study with enanthate

Trial with five dose levels5 61 young men, 20 weeks
Level 3 of 5 +3.4 kg
Level 4 of 5 +5.2 kg
Level 5 of 5 (highest) +7.9 kg

Same testosterone, different ester. Strength, haemoglobin and muscle volume rose with the level while fat mass and HDL cholesterol fell.

Bright lab bench with sample tubes, symbolic image for research on Testosterone Decanoate
Studied mainly in male contraception research. Symbolic image.

Research status

Where the research stands

There is no registered trial with the single ester. Shown are trials with the approved blend of four testosterone esters, in which decanoate is the longest component. As of 26 Oct 2026. 7

  1. Preclinical Pharmacology of esterification and depot action
  2. Phase 1 1 trial, 0 completed
  3. Phase 2 no registered trial
  4. Phase 3 1 trial, 1 completed
  5. Approval not as a single ester
0 participants in phase 3 Not approved as a single ester. Testosterone Decanoate is part of a blend of four testosterone esters that has been approved in the UK since 28 February 1973.6
Show all 9 phase 3 and 4 trials on a timelineHide timeline 9 completed 0 running 0 with results
Phase 3
Phase 4

Bar: start to primary endpoint (planned for running trials). Green = completed, blue = progress until 26 Oct 2026. Phase 1: 1 trial on safety and pharmacokinetics, not shown as bars.

Side effects

Decanoate shares the risk profile of every testosterone ester; the long ester only changes the pace. Because the compound stays in the depot for a long time, side effects also fade more slowly after stopping.

  • Estrogen: water retention, rising blood pressure, gyno risk with high aromatization.
  • Hematocrit: rises with the dose, keep an eye on the blood count.
  • HPTA suppression: LH, FSH and sperm production are suppressed and the testes can shrink.
  • Lipids: HDL falls as the dose goes up.
  • Androgenic: acne, oily skin, hair loss if predisposed.

Practice

Testosterone, estradiol, hematocrit, lipids and liver values are usually checked before the start and every few weeks. An aromatase inhibitor is used only according to bloodwork, not by default. Because decanoate keeps acting for a long time, a post-cycle plan starts later than with short esters.

  • Banned in official competition (WADA S1).
  • Detectable for a long time, even weeks after the last dose.
Bright desk with notes on blood values, symbolic image for regular checks
Bloodwork before the start and every few weeks. Symbolic image.

Storage

Keep the oil at room temperature, in the dark and tightly closed. Do not put it in the fridge, as the compound can crystallize in the cold. If crystals do show up, warm the vial (in your hand or in warm water) and swirl until the solution is clear again.

Four glass vials with golden oil on a white shelf, next to them a folded light blue cloth
Store at room temperature and in the dark, not in the fridge. Symbolic image.

Related

Related compounds

Same receptors or blends with Testosterone Decanoate: all in the TPD lexicon.

Testosterone Decanoate
Testosterone Enanthate Long ester, same effect, faster release Testosterone Cypionate Long ester Testosterone Undecanoate Ultra-long ester, even less frequent Testosterone Phenylpropionate Medium-length ester, often blended with decanoate Testosterone Propionate Short ester Deca (Nandrolone Decanoate) Same ester on nandrolone Tri-Test One version contains decanoate plus cypionate and enanthate Test Mix (high dose) Contains decanoate plus three more esters

FAQ

Common questions about Testosterone Decanoate

Short answers, each backed by the sources below.

How long does one injection last?

Long. With an injection every four weeks trough levels rose with each injection, one week after the fourth injection the peak was 31 nmol/L and thus briefly above the normal range. In the phase IIb study trough levels were in the normal range with 4-week intervals and just below it with 6 weeks.12

Is Testosterone Decanoate approved?

Not as a single ester. Decanoate is the longest component of a blend of four testosterone esters that has been approved since 28 February 1973 according to the UK product information. The registry has no trial with decanoate alone, only trials with this blend, most of them after approval. Everything here is the state of research, not a recommendation.67

What happens to the body's own hormone production and fertility?

LH and FSH fell quickly and kept falling during use. Together with a progestin implant all 20 men had at most 1 million sperm per ml after 12 weeks, 80 percent had none. In the phase IIb study sperm counts and gonadotropins recovered in both groups after stopping.12

Which side effects were seen?

Haemoglobin rose by 9 and haematocrit by 15 percent, along with body weight. One study was stopped after 12 to 18 weeks because some men had raised liver values. In the phase IIb study there were minor effects on weight and cholesterol, 14 men stopped because of a side effect.12

Does the effect depend on the amount?

For testosterone in general, yes. In a trial with five dose levels (with enanthate, the body's own production switched off) fat-free mass rose by 3.4, 5.2 and 7.9 kg in the three higher levels. Strength and haemoglobin rose with the level while fat mass and HDL cholesterol fell.5

How long is decanoate detectable?

In a doping control study with a four-ester blend all esters were detectable in blood and detection time depended on the ester. Samples were taken over 60 days. Testosterone is banned in official competition.3

Glossary

Terms explained briefly

Dotted words in the text open these explanations directly.

Androgen receptor
Protein inside the cell that testosterone binds to. Genes are then read, for example for muscle building.
Azoospermia
No sperm detectable in the ejaculate.
Crystallisation
In the cold the compound drops out of the oil as fine crystals. Warming and swirling dissolve them again.
Depot
The oil solution stays in the muscle after the injection and releases the compound over weeks.
Ester
An attached fatty acid chain. The longer it is, the more slowly testosterone is released from the oil depot. It is split off in the blood.
Gonadotropins (LH and FSH)
Pituitary hormones. LH drives testosterone production in the testes, FSH drives sperm production.
Haematocrit
Share of red blood cells in the blood. If it rises a lot, the blood gets thicker.
Hormone axis (HPTA)
Hypothalamus, pituitary and testes together control the body's own testosterone production. Testosterone from outside suppresses this axis.
Progestin
Hormone from the corpus luteum hormone group. In male contraception research it additionally suppresses LH and FSH.
Trial phases
Phase 1 tests tolerability in a few people, phase 2 looks for the dose, phase 3 confirms benefit and safety in many. Phase 4 runs after approval.
Trough level
The lowest value just before the next injection.

Practice

PCT / after coming off

Anabolic substances suppress the body's own testosterone production in the research context. Anyone who comes off a cycle (rather than running it continuously) typically uses a post-cycle therapy (PCT) to restart the natural axis (HPTA).

The standard scheme in the research/literature context combines a SERM (tamoxifen and/or clomifene, alternatively enclomiphene) over roughly four weeks, optionally preceded by HCG to re-sensitise the testes before the SERM block. An aromatase inhibitor (anastrozole/exemestane) belongs more to on-cycle estrogen control than to the PCT itself.

Tip: order the PCT items together with the cycle so they are already on hand when you come off.

This information serves research and educational purposes only. Not medical advice.

Tamoxifen (Nolvadex) SERM, core of PCT View Clomid (Clomifen) SERM, core of PCT View Enclomiphene (Androxal) SERM alternative View HCG testicular restart before PCT View Arimidex (Anastrozole) aromatase inhibitor, on-cycle View Aromasin (Exemestane) aromatase inhibitor, on-cycle View

Evidence

Sources

Show all 8 sourcesHide sources 5 Studies1 Trial registry2 Database checked 26 Oct 2026

Studies

  1. Decanoate every 4 weeks with a progestin implant: levels, hormone axis and sperm

    Anderson et al., Contraception, 2002

    DOI 10.1016/s0010-7824(02)00390-6 PMID 12443967
    Checked 26 Oct 2026 via doi.org, Crossref, PubMed
  2. Phase IIb study over 48 weeks, 4- or 6-week intervals

    Hay et al., Journal of Clinical Endocrinology and Metabolism, 2005

    DOI 10.1210/jc.2004-0895 PMID 15671109
    Checked 26 Oct 2026 via doi.org, Crossref, PubMed
  3. Detection of testosterone esters in blood

    Forsdahl et al., Drug Testing and Analysis, 2015

    DOI 10.1002/dta.1914 PMID 26695486
    Checked 26 Oct 2026 via doi.org, Crossref, PubMed
  4. Pharmacology of anabolic steroids, review

    Kicman, British Journal of Pharmacology, 2008

    DOI 10.1038/bjp.2008.165 PMID 18500378
    Checked 26 Oct 2026 via doi.org, Crossref, PubMed
  5. Dose response in young men, five levels over 20 weeks

    Bhasin et al., American Journal of Physiology: Endocrinology and Metabolism, 2001

    DOI 10.1152/ajpendo.2001.281.6.E1172 PMID 11701431
    Checked 26 Oct 2026 via doi.org, Crossref, PubMed

Trial registry

  1. Trials with the four-ester blend on ClinicalTrials.gov

    ClinicalTrials.gov, U.S. National Library of Medicine

    Checked 26 Oct 2026 via ClinicalTrials.gov API v2

Database

  1. Product information of the four-ester testosterone blend (UK)

    electronic medicines compendium (emc), Zusammensetzung und Datum der ersten Zulassung

    Checked 26 Oct 2026 via medicines.org.uk
  2. Mechanism of testosterone in ChEMBL

    ChEMBL, EMBL-EBI (CHEMBL386630)

    Checked 26 Oct 2026 via ChEMBL

In the shop

Testosterone Decanoate in the catalog

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