Pharmacokinetics (ADME)
Pharmacokinetics refers to how a drug moves through the body over time. The four stages of this process—Absorption, Distribution, Metabolism, and Excretion (ADME)—determine how efficiently and for how long an anabolic steroid exerts its effects.
Understanding ADME is critical for:
- Planning dose timing and injection frequency
- Managing oral vs. injectable differences
- Anticipating side effects and toxicity
- Timing bloodwork and post-cycle therapy (PCT)
A – Absorption
Absorption refers to how the steroid enters the bloodstream after administration. It depends on the route of administration (oral, intramuscular, subcutaneous) and formulation (ester, alkylation, carrier oil).
| Route | Characteristics | Bioavailability |
|---|---|---|
| Oral (e.g., Dianabol, Superdrol) | Rapid absorption via GI tract | Low to moderate (5–30%) |
| Injectable (e.g., Test E, Deca) | Depot formation in muscle; slow release | ~100% |
| Subcutaneous (e.g., hCG, peptides) | Diffuses through fat into blood | High |
| Buccal/Nasal (rare for AAS) | Direct to bloodstream via mucosa | High, but rarely used for steroids |
Key Points:
- C17α-alkylation allows oral steroids to survive first-pass liver metabolism
- Injectables bypass the liver on first pass, reducing hepatic stress
- Absorption rate of injectables is heavily influenced by ester length and injection site
D – Distribution
Once in the bloodstream, the steroid is distributed to tissues throughout the body. Steroids are lipophilic, meaning they tend to accumulate in fat and muscle tissues.
- Bind to sex hormone-binding globulin (SHBG) and albumin
- Only free hormone is biologically active
- Higher doses = more free hormone saturation = more anabolic effect
Factors influencing distribution:
- Plasma protein binding affinity
- Muscle mass and fat percentage
- Concurrent medications or supplements (e.g., competing for albumin)
Note: Some steroids (e.g., Trenbolone) exhibit high tissue affinity, leading to more potent effects at lower serum levels.
M – Metabolism
Metabolism refers to the chemical modification of the steroid, primarily in the liver. The liver converts active steroids into inactive metabolites for eventual excretion.
Key metabolic processes:
- Phase I (modification): Hydroxylation, oxidation, reduction
- Phase II (conjugation): Glucuronidation, sulfation
| Compound Class | Liver Metabolism | Notes |
|---|---|---|
| C17α-alkylated orals | High hepatotoxicity risk | Use TUDCA/NAC; short durations only |
| Injectable steroids (non-alkylated) | Mild liver impact | Lower concern unless stacked with orals |
| DHT-derivatives (e.g., Winstrol, Masteron) | Unique reduction pathways | May have poor aromatization profiles |
Enzyme Impact:
- CYP450 enzymes (especially CYP3A4) are responsible for steroid breakdown
- Certain drugs (e.g., grapefruit juice, antifungals) may inhibit or accelerate steroid metabolism
E – Excretion
Steroids are excreted primarily via:
- Urine (major pathway)
- Bile and feces (minor)
- Sweat (trace)
Once metabolized by the liver, conjugated steroid metabolites are excreted by the kidneys. Drug detection times depend on:
- Ester length (see: esters_and_half_lives)
- Fat solubility
- Frequency and duration of use
| Compound | Detection Time (approx.) | Notes |
|---|---|---|
| Testosterone Propionate | ~2–3 weeks | Short ester, fast clearance |
| Testosterone Enanthate | ~3–4 weeks | Moderate ester |
| Nandrolone Decanoate | ~18 months | Long half-life and lipophilicity |
| Oral Turinabol | ~40–50 days | Active metabolite detectable for weeks |
Tip: Long esters and fat-soluble compounds persist longer and delay PCT start time.
Practical Implications for Bodybuilders
- Timing injections based on absorption and ester clearance is key to stable hormone levels
- Metabolism rate varies—some users clear orals rapidly, others accumulate liver strain
- Drug testing windows vary wildly based on ADME properties
- PCT planning should always account for metabolic clearance
Real-World Advice (r/steroids PDF)
- “My orals kick in fast, but crash just as fast. Timing matters.”
- “I ran Deca without waiting long enough for PCT—never again.”
- “Always pin test E every 3.5 days. Once a week gave me mood swings.”
- “Bloodwork timing is everything—wait until esters clear or your labs will lie.”
Summary
- Absorption = how fast the compound enters the blood
- Distribution = where the steroid travels and accumulates
- Metabolism = how the body modifies and deactivates the steroid
- Excretion = how the steroid leaves the body
Understanding the pharmacokinetics of AAS empowers users to plan smarter cycles, avoid toxicity, and support long-term health.