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Test Base (Testosterone Suspension) - Research Substance

Aqueous suspension of pure testosterone without ester for rapid absorption in research contexts.

2 min read 9 sources

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Glass vial with clear liquid and a blue cap on a white podium with a glowing ring, next to it a large blue 3D steroid molecule in front of a bright lab
Compound approved · testosterone itself, no study of the suspension

Summary

At a glance

Sources checked on 25 Oct 2026

Half-life in blood
56 minutes

Testosterone without an ester, straight into a vein, 11 older men. From a depot it lasts longer1

Short ester for comparison
48 hours

Testosterone propionate kept levels above the normal range this long after one injection2

Ester-free crystal as a pellet
2.5 months

Half-release time of pellets of pure testosterone under the skin, 43 men4

Fat-free mass, highest level
+7.9 kg

Testosterone as enanthate, 20 weeks, highest of five study doses6

  • Test Base is testosterone without an ester, as a suspension in water. It is the same compound as in every testosterone ester and acts on the androgen receptor.9
  • Without an ester testosterone is cleared quickly from the blood: given straight into a vein its half-life was about 56 minutes. How long an injection lasts therefore depends mainly on the depot.1
  • There is no measurement of the suspension itself. Pressed crystals without an ester under the skin released testosterone evenly over months while a short ester like propionate kept levels raised for about 48 hours.42
  • The effect depends on the amount: fat-free mass and haemoglobin rose with the testosterone level while fat mass and HDL cholesterol fell. The body's own hormone axis is suppressed.64
  • According to ChEMBL testosterone is an approved drug; the registry lists no trial for the ester-free suspension. Everything here is the state of research, not a recommendation.98
Profile

Updated June 2026

How long does it stay in the body?

Share left after one dose, calculated with a half-life of ~5 hours

Half-life ~5 hours
After 10 hours: 25 %
Hour 5 · 50 %Hour 10 · 25 %Hour 15 · 12.5 %Hour 25 · 3.1 %

Simplified model without an absorption phase, half-life from the TPD lexicon. The lexicon gives 4 to 6 hours, we calculate with the middle.

Class
Testosterone

pure hormone, no ester

Use
Research substance

HRT context explored

Half-life
Approx. 4-6 hours

very short

Status
Controlled

WADA banned in sport context

Sizes
100mg/ml

1 size in the shop

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

What is Test Base?

Test Base is a sterile aqueous suspension of pure testosterone without ester. Unlike esterified testosterones (such as enanthate or cypionate), Test Base is absorbed very rapidly and has a short half-life of about 4-6 hours. This form is investigated in research contexts, primarily to produce rapid blood level fluctuations.

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

Comparison

No ester to very long ester

The same compound at the same receptor, with and without an ester, as stated in the TPD lexicon. Tap a card to open its entry.

No ester, in water Test Base (Testosterone Suspension) - Research Substance AR
No ester, in water Test Suspension AR Short ester Testosterone Propionate AR Long ester Testosterone Enanthate AR Very long ester Testosterone Undecanoate AR

Simplified: the ester only sets how fast testosterone is released from the depot. Without an ester only the form of the depot decides. 123

How it works

Testosterone is the primary male sex hormone and binds to the androgen receptor with high affinity. It promotes protein synthesis, bone density, erythropoiesis and sexual function. Test Base without ester is rapidly absorbed, leading to rapid changes in blood levels.

  • Direct androgen receptor agonist
  • Promotes protein synthesis and nitrogen retention
  • Increases erythrocyte production
  • Rapid absorption and elimination

Where it acts

Where testosterone acted in studies

Tap a point or a card. Grey = observed in studies, data from studies with testosterone, not with the suspension.

  1. Pituitary

    LH and FSH fell clearly while testosterone came from outside4

    Observed in trials
  2. Blood

    Estradiol rose just 5 minutes after testosterone into a vein1

    Observed in trials
  3. Skeletal muscle

    Muscle volume and leg strength rose with the dose6

    Observed in trials
  4. Fat tissue

    Fat mass fell as levels rose6

    Observed in trials
  5. Liver and blood lipids

    HDL cholesterol fell as levels rose6

    Observed in trials

Targets in the ChEMBL database9

Compound CHEMBL386630: one recorded mechanism, agonist with direct binding to the human receptor.

Androgen receptor
Gene
AR
UniProt
P10275
ChEMBL
CHEMBL1871
Action
Agonist, direct binding
Blue 3D steroid molecules stream from a glass nozzle and dock glowing onto translucent muscle fibres
Without an ester testosterone reaches the blood quickly and acts on the androgen receptor. 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 clear liquid and a blue cap on a bright lab bench, a syringe lying beside it
Ready to use, shake before every draw. Symbolic image.

What the research shows

Testosterone is the best-documented anabolic hormone. Studies show strong anabolic effects, muscle gain and body composition improvement. Negative effects on lipids and cardiovascular function are also well documented. Test Base is investigated to understand rapid pharmacokinetics.

  • Strong anabolic and androgenization effects
  • Well-documented lipid dysregulation
  • Cardiovascular effects under study
  • HPTA suppression at doses above 100 mg/week

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.

How long testosterone stays in the blood123

Hours, three studies with different measures

No ester, into a vein1 Half-life in blood
No ester 0.9 h
Propionate, into the muscle2 Level above the normal range
Short ester (propionate) 48.0 h
Enanthate, into the muscle3 Until back to baseline
Long ester (enanthate) 216.0 h

Abstract values: 55.93 minutes, 48 hours and 9 days. The three numbers measure different things and only show the order of magnitude. There is no measurement for the ester-free suspension; from a depot in muscle it takes longer than in a vein.

Fat-free mass after 20 weeks6

Gain in kg in the three higher of five dose levels, testosterone as enanthate, the body's own production was switched off with medication

Trial with five dose levels6 61 young men, 20 weeks
Level 3 of 5 +3.4 kg
Level 4 of 5 +5.2 kg
Level 5 of 5 (highest, 600 mg per week) +7.9 kg

The two lowest levels are not shown. Fat mass and HDL cholesterol fell as levels rose while haemoglobin went up. Study with an ester, not with the suspension.

Frosted glass sculpture of a flexed arm on a stainless steel tray with a glass lightning bolt leaning against it
Testosterone is well studied, the ester-free suspension hardly at all. Symbolic image.

Research status

Where the research stands

Testosterone is widely studied, but the registry lists no trial of its own for the ester-free aqueous suspension. As of 25 Oct 2026. 8

  1. Preclinical Release profile in an animal model (monkeys)
  2. Phase 1 no registered trial
  3. Phase 2 no registered trial
  4. Phase 3 no registered trial
  5. Approval testosterone itself, no study of the suspension
Compound approved: ChEMBL lists testosterone with phase 4 as the highest phase. The registry has no trial for the ester-free suspension.9

The approval predates today's trial registries, so the register shows no current trial for this form. 8

Side effects

Testosterone can lead to various side effects:

  • Estrogen-dependent effects (gynecomastia, water retention) - dependent on aromatization
  • Androgenization effects (acne, hair loss, prostate enlargement)
  • Lipid dysregulation (LDL increase, HDL decrease)
  • Blood pressure elevation
  • HPTA suppression and testosterone decline after discontinuation
  • Local injection irritation (aqueous suspension)

Storage

Test Base should be stored at room temperature, protected from light. The aqueous suspension may curdle with prolonged storage. Do not freeze. Shake thoroughly before each injection.

  • Room temperature (15-25°C)
  • Protected from light and heat
  • Do not freeze or overheat
  • Always shake before use

Related

Related compounds

Same receptors or blends with Test Base (Testosterone Suspension) - Research Substance: all in the TPD lexicon.

Test Base (Testosterone Suspension) - Research Substance
Test Suspension Same compound, also without an ester Testosterone Propionate Short ester, more frequent doses Testosterone Enanthate Long ester, best studied Testosterone Cypionate Long ester Testosterone Undecanoate Very long ester, also as a tablet Sustanon 250 Four esters blended

FAQ

Common questions about Test Base (Testosterone Suspension) - Research Substance

Short answers, each backed by the sources below.

What does without an ester mean?

Usual testosterone products carry a fatty acid chain that slows the release. Test Base has none. Given straight into a vein testosterone had a half-life of about 56 minutes. With a short ester (propionate) levels stayed raised for about 48 hours after one injection, with a long ester (enanthate) it took 9 days to return to baseline.123

Why does an injection last longer than an hour?

Because the testosterone first has to dissolve out of the depot. How fast depends on its form: pellets of pressed, pure testosterone under the skin released it evenly, half was released after about 2.5 months and men came back for a new implant after 5.8 months on average. There is no such measurement for the suspension in water.45

Is Test Base approved?

The compound is: the ChEMBL database lists testosterone as an approved drug with phase 4 as the highest phase. ClinicalTrials.gov has no trial for the ester-free aqueous suspension. Testosterone is banned in sport. Everything here is the state of research, not a recommendation.98

Does the effect depend on the amount?

Yes. In a trial with five dose levels over 20 weeks (testosterone as enanthate, highest level 600 mg per week) fat-free mass rose by 3.4, 5.2 and 7.9 kg in the three higher levels. Leg strength, muscle volume and haemoglobin rose with the level while fat mass and HDL cholesterol fell.6

What happens to the body's own hormone production?

Testosterone from outside suppresses the hormone axis. On testosterone pellets LH and FSH fell clearly, the higher the testosterone level the lower. After an enanthate injection LH and FSH stayed suppressed for as long as testosterone was raised.43

Is it converted to oestrogen?

Yes, part of it. After testosterone into a vein estradiol was raised just 5 minutes later and stayed raised until the end of measurement after 3 hours. Circulation and blood pressure did not change.1

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.
Erythropoiesis
Production of red blood cells in the bone marrow. Testosterone stimulates it.
Ester
An attached fatty acid chain. It makes testosterone oil-soluble and slows release from the depot. Test Base has none.
Estradiol
The main oestrogen. In men it is also made from testosterone via the enzyme aromatase.
Fat-free mass
Body weight without fat: muscle, bone, organs and water.
Half-life
Time until half of a substance in the blood has been cleared.
HDL cholesterol
The cholesterol that carries fat away from the vessels. Low values count as a heart risk.
Hormone axis (HPTA)
Hypothalamus, pituitary and testes together control the body's own testosterone production. Testosterone from outside suppresses this axis.
Pellet
Small rod of pressed compound placed under the skin that dissolves slowly.
Suspension
Solid particles floating in a liquid instead of dissolving. That is why it is shaken before use.

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 9 sourcesHide sources 7 Studies1 Trial registry1 Database checked 25 Oct 2026

Studies

  1. Testosterone into a vein, half-life and estradiol

    White et al., Journal of Clinical Pharmacology, 1998

    DOI 10.1002/j.1552-4604.1998.tb00011.x PMID 9753206
    Checked 25 Oct 2026 via doi.org, Crossref, PubMed (Titel und Seiten, Datensatz ohne DOI)
  2. Level over time after testosterone propionate

    Fujioka et al., Journal of Clinical Endocrinology and Metabolism, 1986

    DOI 10.1210/jcem-63-6-1361 PMID 3782423
    Checked 25 Oct 2026 via doi.org, Crossref, PubMed
  3. Level over time after one enanthate injection

    Schürmeyer and Nieschlag, International Journal of Andrology, 1984

    DOI 10.1111/j.1365-2605.1984.tb00775.x PMID 6434435
    Checked 25 Oct 2026 via doi.org, Crossref, PubMed
  4. Pellets of crystalline testosterone without an ester

    Handelsman et al., Journal of Clinical Endocrinology and Metabolism, 1990

    DOI 10.1210/jcem-71-1-216 PMID 2115044
    Checked 25 Oct 2026 via doi.org, Crossref, PubMed
  5. Release and duration of testosterone pellets

    Kelleher et al., Clinical Endocrinology, 2004

    DOI 10.1111/j.1365-2265.2004.01994.x PMID 15049955
    Checked 25 Oct 2026 via doi.org, Crossref, PubMed
  6. 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 25 Oct 2026 via doi.org, Crossref, PubMed
  7. Release profile rather than total dose (primates)

    Weinbauer et al., Journal of Andrology, 2003

    DOI 10.1002/j.1939-4640.2003.tb02739.x PMID 12954670
    Checked 25 Oct 2026 via doi.org, Crossref, PubMed

Trial registry

  1. Search on ClinicalTrials.gov (no matching trial)

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

    Checked 25 Oct 2026 via ClinicalTrials.gov API v2

Database

  1. Mechanism and approval of testosterone in ChEMBL

    ChEMBL, EMBL-EBI (CHEMBL386630)

    Checked 25 Oct 2026 via ChEMBL

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