How Nandrolone Affects SHBG

Sex hormone-binding globulin (SHBG) is a carrier protein produced by the liver that binds testosterone, DHT, and estradiol with high affinity. It regulates how much of each hormone is biologically available at tissue level.

Nandrolone affects SHBG through two distinct mechanisms:

1. Low SHBG binding affinity: Saartok, Dahlberg, and Gustafsson (1984) established that nandrolone has very low relative binding affinity for SHBG compared to testosterone and DHT. This means nandrolone does not compete meaningfully for SHBG binding sites and does not displace other hormones from SHBG in the way that some other AAS do.

2. Suppression of hepatic SHBG synthesis: Like most androgens, nandrolone suppresses the liver's production of SHBG protein. Garevik et al. (2016) documented a statistically significant decrease in SHBG after a single 150 mg injection of nandrolone decanoate. Yuen et al. (2021) confirmed that SHBG suppression is a class effect of 19-nor derived androgens, occurring alongside HDL reduction and haematocrit increase.

The net result is reduced circulating SHBG, which increases the free fraction of all SHBG-bound hormones. For a user on testosterone plus nandrolone, this means:

• More free testosterone per unit of total testosterone
• More free estradiol per unit of total estradiol
• More free DHT per unit of total DHT

The practical implication is that standard total hormone measurements become less informative when SHBG is suppressed. A total estradiol of 30 pg/mL with an SHBG of 12 nmol/L represents substantially more free estradiol activity than the same total E2 with an SHBG of 35 nmol/L.

SHBG on nandrolone:

• Decreased from baseline, typically 30-60% reduction at bodybuilding doses
• Effect begins within the first week and persists throughout the cycle
• Magnitude is dose-dependent and compounds with co-administered testosterone

Downstream effects of suppressed SHBG:

• Free testosterone increases relative to total testosterone
• Free estradiol increases relative to total estradiol
• Total hormone readings become less clinically meaningful
• AI decisions based on total E2 alone may lead to over-treatment or under-treatment

Recovery:

• SHBG normalises within weeks of AAS cessation
• SHBG recovery is typically faster than HPG axis recovery

Order SHBG alongside total estradiol on every nandrolone cycle panel. Without SHBG, total E2 cannot be accurately interpreted.

Calculate free estradiol using the Vermeulen formula (available as online calculators) from total E2, SHBG, and albumin. This provides a more clinically useful number than total E2 alone.

Timing: Baseline, week 4, week 8. SHBG should be checked each time estradiol is assessed.

Interpretation guide:

• SHBG below 15 nmol/L with "normal" total E2 (25-35 pg/mL): free E2 activity is likely elevated. Watch for estrogenic symptoms
• SHBG below 10 nmol/L: most total hormone readings are clinically unreliable. Free hormone calculations or symptoms should guide management

• Always check SHBG when interpreting estradiol on nandrolone. A "normal" total E2 can mask elevated free E2 activity
• If experiencing estrogenic side effects (water retention, gynecomastia sensitivity) despite a normal total E2, check SHBG. Suppressed SHBG is likely the explanation
• Conservative AI dosing is appropriate when SHBG is very low because the free E2 fraction is disproportionately high relative to total E2
• Do not chase a specific SHBG number. SHBG suppression on AAS is expected and not directly harmful. The clinical value is in using SHBG to interpret other hormone levels correctly
• After stopping nandrolone, SHBG recovers within weeks, well before HPG axis function normalises