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NPP

Nandrolone Phenylpropionate

NPP (nandrolone phenylpropionate) is a short-ester injectable form of nandrolone (19-nortestosterone), an anabolic-androgenic steroid (AAS) of the injectable 19-nor class. The phenylpropionate ester only changes how fast the drug is released; the active hormone is identical to that in the more heavily studied nandrolone decanoate ("Deca"), so almost all human evidence comes from the decanoate ester or from AAS as a class. There is essentially no published human data on NPP itself. Nandrolone reliably increases lean body mass and stimulates red-cell production, which is why it has been studied clinically for HIV/COPD wasting. The main dangers are cardiovascular: long-term AAS users show reduced systolic and diastolic heart function plus accelerated coronary plaque. Nandrolone also strongly suppresses the body's own testosterone production (HPTA), and because it has progestogenic activity it commonly causes sexual dysfunction ("deca dick"). Recovery of natural hormone function after 19-nor use can be slow and should be managed by an endocrinologist. This monograph is risk-forward and is not dosing guidance; any reported doses are clinical-trial doses cited only to anchor their associated risks.

Clinical readoutAAS · injectable-19nor
Hepatic strainLow
CardiovascularHigh
HPTA suppressionVery high
Half-life
4.3 h
Route
Deep intramuscular inje…
Evidence
C
Active
Clinically meaningful a…
4.3 h8.6 h12.9 h17.2 h21.5 h
Illustrative single-compartment washout · each mark = one half-life · t½ ≈ The free (unesterified) nandrolone molecule has a very short terminal half-life (~4.3 hours). The phenylpropionate ester slows release from the intramuscular depot, giving an effective half-life on the order of ~2-3 days (shorter than nandrolone decanoate at ~6-12 days). Note: NPP-specific human pharmacokinetic data are sparse; these values are largely extrapolated from nandrolone ester pharmacology.
Pharmacology

Mechanism of action

Nandrolone is a synthetic derivative of testosterone lacking the C19 methyl group (19-nortestosterone). It binds the androgen receptor with high affinity and drives androgen-receptor-mediated gene transcription, promoting skeletal muscle protein synthesis and erythropoiesis. Unlike testosterone, in tissues rich in 5-alpha-reductase (scalp, skin, prostate) nandrolone is converted to dihydronandrolone (DHN), a metabolite with weaker androgenic activity than DHT, which underlies its comparatively lower androgenic:anabolic profile in those tissues. Nandrolone aromatizes to estrogen only weakly but has intrinsic progestogenic (progesterone-receptor) activity, which contributes to its distinct side-effect pattern (sexual dysfunction, potential prolactin elevation). Like all exogenous androgens it exerts negative feedback on the hypothalamic-pituitary axis, suppressing LH and FSH and therefore endogenous testosterone and spermatogenesis. The phenylpropionate ester is cleaved by esterases after intramuscular injection to release free nandrolone; it does not alter the drug's mechanism, only its release kinetics.
Kinetics

Pharmacokinetics

Half-life

The free (unesterified) nandrolone molecule has a very short terminal half-life (~4.3 hours). The phenylpropionate ester slows release from the intramuscular depot, giving an effective half-life on the order of ~2-3 days (shorter than nandrolone decanoate at ~6-12 days). Note: NPP-specific human pharmacokinetic data are sparse; these values are largely extrapolated from nandrolone ester pharmacology.

Active duration

Clinically meaningful androgen exposure for roughly 3-7 days per injection, which is why the short ester is administered more frequently than decanoate. Detection window is far longer: the urinary metabolite 19-norandrosterone can remain detectable for weeks to months, relevant for washout planning and clinician awareness, not for evasion.

Route

Deep intramuscular injection of an oil-based solution. No oral form.

Metabolism & clearance

Hepatic metabolism with 5-alpha-reduction to dihydronandrolone and further reduction/conjugation; excreted renally, principally as 19-norandrosterone and related 19-nor metabolites. Not 17-alpha-alkylated, so it does not undergo the first-pass hepatic burden characteristic of oral AAS.

For monitoring and washout planning, not drug-test evasion.

Reported effects

Physiological & performance effects

  • Increases lean body mass / fat-free mass; in an RCT in HIV-infected men with weight loss, 150 mg nandrolone decanoate IM every 2 weeks increased lean body mass significantly more than placebo and comparably to rhGH (PMID 15914526)
  • Stimulates erythropoiesis: raises hemoglobin and erythropoietin, demonstrated in a placebo-controlled COPD rehabilitation RCT (PMID 14605042)
  • Increases intracellular/body cell mass without expanding extracellular water in clinical wasting populations (PMID 14605042; PMID 15914526)
  • Improved self-reported sexual function versus placebo specifically in hypogonadal/wasting HIV-infected men (PMID 15914526) - the opposite effect (sexual dysfunction) is typical in eugonadal users because of HPTA suppression and progestogenic activity
  • Studied historically as a component of male hormonal contraception because 19-nortestosterone/nandrolone androgens strongly suppress LH, FSH and spermatogenesis (PMID 14667989)
Safety

Adverse effects by system

Cardiovascular

Class-level AAS cardiotoxicity is the leading concern. Long-term illicit AAS users show reduced left ventricular systolic function (lower LVEF), impaired diastolic (early relaxation) function, and greater coronary atherosclerotic plaque volume than non-users, with lifetime dose correlating with plaque burden (PMID 28533317). A separate cross-sectional study found severely reduced biventricular function persisting even in former users (PMID 37992194). Individual cases of severe AAS-associated cardiomyopathy that partially reversed after cessation are reported (PMID 31287235). These data are on AAS broadly, not NPP specifically.

Hepatic

Nandrolone is not 17-alpha-alkylated, so clinically significant hepatotoxicity/cholestasis is much less expected than with oral AAS, and no adequate NPP-specific human hepatotoxicity data exist. Preclinical work shows supraphysiologic nandrolone impairs hepatic mitochondrial membrane potential and redox homeostasis in mice (PMID 33984388), a mechanistic signal of possible liver stress that has not been characterized in humans.

Endocrine / HPTA

Strong, dose-dependent suppression of LH, FSH and endogenous testosterone via negative feedback, consistent with 19-nortestosterone/nandrolone androgens' documented use as a basis for male hormonal contraception (PMID 14667989). Progestogenic activity may also elevate prolactin and contribute to endocrine side effects. Recovery can be prolonged after 19-nor compounds.

Reproductive

Testicular atrophy, suppressed spermatogenesis and oligo-/azoospermia occur due to gonadotropin suppression; 19-nortestosterone/nandrolone androgens strongly suppress LH, FSH and spermatogenesis, which is the basis of their historical study as male contraceptives (PMID 14667989). Progestogenic activity plus low endogenous testosterone commonly cause erectile dysfunction and reduced libido in non-hypogonadal users (the 'deca dick' phenomenon); note that in hypogonadal HIV-wasting men nandrolone instead improved sexual function (PMID 15914526), so effect direction depends on baseline androgen status.

Neuropsychiatric

AAS use is associated with hypomanic/manic symptoms, irritability and aggression during use, and depressive symptoms during withdrawal; a dependence syndrome occurs in a minority of users (PMID 19769977). Severe aggression/violence has been described in case reports (PMID 8773655). These effects are idiosyncratic and affect only a subset of users; data are class-level, not NPP-specific.

Renal

No adequate NPP-specific human renal data. AAS use as a class has been linked in case reports to renal injury, but no primary source is cited here for a nandrolone-specific renal effect; this is a data gap and renal function should still be monitored.

Hematologic

Increased erythropoiesis with rises in hemoglobin and erythropoietin (PMID 14605042); at supraphysiologic doses this raises the risk of polycythemia/elevated hematocrit and secondary thrombotic risk, which is a monitoring priority even though the trial doses were modest.

Dermatologic

Limited nandrolone-specific human data. Because scalp/skin 5-alpha-reduction yields the weaker metabolite dihydronandrolone, androgenic skin effects (acne, oily skin, male-pattern hair loss) may be somewhat less pronounced than with testosterone, but they can still occur; no adequate NPP-specific human dataset quantifies this.

Recovery

HPTA suppression & recovery

Suppression: Strong / marked - 19-nor compounds suppress LH, FSH and endogenous testosterone, and suppression from a 19-nor can be more stubborn to recover than from testosterone

Exogenous 19-nortestosterone/nandrolone androgens strongly suppress LH, FSH and testosterone (PMID 14667989), and endogenous production does not immediately resume when the drug stops; the progestogenic activity may compound suppression. Recovery timelines are individual and can be prolonged. Anyone concerned about fertility or hormonal recovery should be evaluated and managed by an endocrinologist with baseline and follow-up bloodwork. If pharmacologic recovery support is considered, that is a clinical decision made under specialist supervision; this monograph does not recommend any specific restart protocol and addresses only single-agent (single-SERM) approaches conceptually, deferring entirely to a physician.

Bloodwork & vitals

Monitoring

Recommended labs & checks
Complete blood count with hematocrit/hemoglobin (polycythemia surveillance)Lipid panel (HDL suppression / atherogenic shift)Blood pressureLH, FSH, total testosterone, estradiol and prolactin (HPTA suppression and progestogenic effects)Liver enzymes (ALT, AST, bilirubin) as a precautionRenal function (creatinine, eGFR)PSA and prostate assessment in older usersConsider baseline and follow-up echocardiography for long-term or high-dose users given documented systolic/diastolic dysfunction (PMID 28533317; PMID 37992194)

Cadence: Baseline before any use, then periodically during use (e.g., every 8-12 weeks for CBC/lipids/blood pressure) and again after cessation to document HPTA recovery. Cardiac imaging is not routine but warranted with symptoms or long-term use. All monitoring should be arranged with and interpreted by a clinician.

Warning signs — seek care
  • Chest pain, exertional breathlessness, palpitations, or reduced exercise tolerance (possible cardiomyopathy/ischemia) - seek urgent care
  • Leg swelling or signs of heart failure
  • Headache, flushing, visual changes, or very high hematocrit (hyperviscosity/thrombotic risk)
  • New or worsening aggression, mania, or depressive/suicidal thoughts (including during withdrawal)
  • Persistent erectile dysfunction, loss of libido, or testicular shrinkage
  • Jaundice, dark urine, or right-upper-quadrant pain
  • Signs of a blood clot (calf pain/swelling, sudden shortness of breath)
Do not use if

Contraindications

  • Known or suspected prostate or breast carcinoma (androgen-dependent malignancies)
  • Pregnancy and breastfeeding (androgenic; virilization risk to a female fetus)
  • Pre-existing cardiovascular disease, heart failure, cardiomyopathy, or significant coronary artery disease, given documented AAS cardiotoxicity (PMID 28533317; PMID 37992194)
  • Polycythemia or elevated hematocrit, given nandrolone's erythropoietic effect (PMID 14605042)
  • History of AAS-associated mood disorder, aggression, or dependence (PMID 19769977)
  • Desire to preserve fertility in the near term (suppresses spermatogenesis; PMID 14667989)
  • Significant hepatic dysfunction (precautionary, despite lower expected hepatotoxicity than oral AAS)
  • Uncontrolled hypertension or dyslipidemia
Combinations

Interaction profile

  • MajorWith another anabolic steroid: Additive cardiovascular strain
  • MajorWith a thermogenic stimulant: Additive cardiovascular strain
  • ModerateWith thyroid hormone: Additive cardiovascular strain
  • ModerateWith growth hormone: Additive cardiovascular strain
  • MajorWith another anabolic steroid: Blood / clotting
  • MajorWith a clot-promoting SERM: Blood / clotting
  • ModerateWith an aromatase inhibitor: Hormonal
  • ModerateWith an anabolic steroid: Hormonal
  • ModerateWith another 19-nor (progestogenic) steroid: Hormonal
  • ContraindicatedWith DNP: Additive cardiovascular strain

Check a specific combination in the interaction checker.

Harm reduction

Reducing harm & when to stop

  • Understand that NPP has essentially no human safety data of its own; risk estimates are borrowed from nandrolone decanoate and from AAS as a class, so uncertainty is high.
  • Get baseline bloodwork and a blood-pressure check with a clinician before any use, and repeat periodically; do not rely on how you feel to detect cardiovascular or hematologic harm.
  • Cardiovascular damage can persist even after stopping (PMID 37992194) - the safest choice is not to use; if you do, treat any chest pain, breathlessness, or palpitations as an emergency.
  • Watch hematocrit: rising red-cell mass increases clot risk; report headaches, flushing, or shortness of breath.
  • 19-nor compounds are notorious for sexual dysfunction and for slow, sometimes incomplete recovery of natural testosterone - plan any HPTA-recovery evaluation with an endocrinologist, not by self-medicating.
  • Stop and seek care for: jaundice, severe mood changes or suicidal thoughts, signs of a clot, or heart-failure symptoms (leg swelling, exertional breathlessness).
  • If fertility matters to you, know that spermatogenesis is suppressed (PMID 14667989) and recovery is not guaranteed on any timeline.
  • Never share needles and use sterile injection technique to reduce infection and vascular injury risk; this monograph does not cover sourcing of the drug itself.
Evidence

Citations (9)

Every clinical claim above is tied to a primary source. Overall evidence grade C — graded to the best available evidence for its core claims.

  1. 01

    Nandrolone (decanoate ester) increases lean body mass in HIV-infected men with weight loss, comparably to rhGH and more than placebo, and improved self-reported sexual function in this hypogonadal population; trial dose was 150 mg IM every 2 weeks.

    RCTA randomized, placebo-controlled trial of nandrolone decanoate in human immunodeficiency virus-infected men with mild to moderate weight loss with recombinant human growth hormone as active reference treatment.PMID 15914526 ↗

  2. 02

    Nandrolone decanoate increases fat-free mass and raises erythropoietic parameters (hemoglobin, erythropoietin) versus placebo; trial dose was 50 mg IM every 2 weeks in COPD rehabilitation.

    RCTA role for anabolic steroids in the rehabilitation of patients with COPD? A double-blind, placebo-controlled, randomized trial.PMID 14605042 ↗

  3. 03

    Long-term illicit AAS use is associated with reduced LV systolic and diastolic function and greater coronary atherosclerotic plaque volume, with lifetime dose correlating with plaque burden.

    CohortCardiovascular Toxicity of Illicit Anabolic-Androgenic Steroid UsePMID 28533317 ↗

  4. 04

    Severely reduced biventricular myocardial function is found in both current and former long-term AAS users.

    CohortSevere biventricular cardiomyopathy in both current and former long-term users of anabolic-androgenic steroids.PMID 37992194 ↗

  5. 05

    AAS-associated cardiomyopathy can be severe and is at least partially reversible after discontinuation in individual cases.

    Case reportStrong muscles, weak heart: testosterone-induced cardiomyopathy.PMID 31287235 ↗

  6. 06

    AAS use is associated with hypomanic/manic and aggressive symptoms during use, depressive symptoms during withdrawal, and a dependence syndrome in a minority of users.

    ReviewIllicit anabolic-androgenic steroid use.PMID 19769977 ↗

  7. 07

    High-dose anabolic steroid use has been implicated in severe aggression and violent behavior, and in withdrawal/dependence problems.

    ReviewAnabolic steroids and the mind.PMID 8773655 ↗

  8. 08

    Supraphysiologic nandrolone impairs cardiac and hepatic mitochondrial function and redox status in mice (mechanistic signal of heart and liver stress; not human data).

    PreclinicalAnabolic-androgenic steroids impair mitochondrial function and redox status in the heart and liver of mice.PMID 33984388 ↗

  9. 09

    19-nortestosterone/nandrolone androgens strongly suppress LH, FSH and spermatogenesis, driving azoospermia (basis of their study as male contraceptives).

    ReviewPMID 14667989 ↗

Last reviewed 2026-07-06 · Verified against PubMed · Educational, not medical advice