Prolactin

Prolactin is a single-chain peptide hormone secreted by anterior pituitary lactotroph cells. Unlike most pituitary hormones, prolactin secretion is under tonic dopaminergic inhibition rather than hypothalamic releasing-factor stimulation — dopamine from hypothalamic tuberoinfundibular neurons binds D2 receptors on lactotrophs and continuously suppresses prolactin release. Disinhibition (loss of dopamine signal) produces hyperprolactinaemia; sustained dopamine agonism (cabergoline, bromocriptine) suppresses prolactin to low-normal.

Reference range, adult male:

– Serum prolactin: <15–20 ng/mL (assay-dependent)
– Mild elevation: 20–40 ng/mL — investigate cause, manage symptomatically
– Moderate elevation: 40–100 ng/mL — pituitary MRI workup if persistent
– Severe elevation: >100 ng/mL — almost always pituitary adenoma; immediate workup

Causes of elevation in AAS users:

– 19-nor compounds (nandrolone, trenbolone): the dominant AAS-related cause. Mechanism: nandrolone metabolites activate the progesterone receptor on lactotrophs, producing PR-mediated prolactin secretion that bypasses dopamine inhibition. Trenbolone shows similar PR activation plus possible direct effects.
– GH and peptide protocols: somatropin and ghrelin-receptor agonists (GHRP-2, GHRP-6, ipamorelin, hexarelin) can elevate prolactin transiently. Effect is dose-dependent and usually subclinical.
– Stress and exercise: intense training, sleep deprivation, and chronic stress elevate prolactin via central pathways. Pre-test conditions affect serum measurement; standardise the draw morning rested.
– Medications: antipsychotics, SSRIs at high dose, opioids, and antiemetics elevate prolactin via central dopamine antagonism.
– Pituitary prolactinoma: the rare but clinically critical cause. Adenoma of pituitary lactotroph cells producing autonomous prolactin secretion. Prevalence ~10% of incidentalomas on pituitary imaging.

Clinical syndrome of hyperprolactinaemia in males:

– Libido reduction and erectile dysfunction
– Galactorrhoea (rare in males but documented)
– Gynaecomastia in extended cases
– Suppressed LH/FSH secondary to prolactin’s inhibitory effect on GnRH pulsing
– Headache, visual field defects (with macroprolactinoma compressing optic chiasm)

The “deca dick” pattern users describe is prolactin-mediated libido loss with normal serum testosterone — the cause is not androgen deficiency but central dopamine-prolactin signalling. No amount of testosterone addition resolves the symptom; prolactin reduction does.

Cabergoline intervention:

Cabergoline is the standard pharmacological intervention. Mechanism: long-acting D2 dopamine receptor agonist; binds with high affinity and dissociates slowly, producing sustained prolactin suppression on twice-weekly dosing. Standard protocol: 0.25 mg twice weekly, titrate upward to 0.5 mg twice weekly if needed. Melmed et al. 2011, J Clin Endocrinol Metab Endocrine Society guidelines on hyperprolactinaemia diagnosis and treatment recommend cabergoline as first-line over bromocriptine due to superior efficacy and tolerability.

Cabergoline at supraphysiological doses (used in Parkinson’s disease at 4+ mg/day) carries cardiac valvulopathy risk through 5-HT2B receptor activation; the AAS-relevant dose range (0.25–1 mg/week) is well below this threshold and the cardiac risk has not been documented at this dosing.

Progestogenic gynaecomastia — the missed diagnosis:

19-nor compounds produce gynaecomastia through progestogenic activation of mammary progesterone receptor, sensitising breast tissue to circulating estradiol at concentrations that would be subclinical in non-progestogen-exposed users. The presentation looks identical to estrogenic gynaecomastia — retroareolar firm tissue, sensitivity — but estradiol bloodwork reads normal and standard AI intervention fails. Treatment requires both prolactin reduction (cabergoline) and breast-tissue ER blockade (tamoxifen). Bloodwork: prolactin, sensitive E2, total and free testosterone, SHBG. Prolactin >20 ng/mL with palpable breast tissue on a 19-nor cycle confirms the mechanism.

Persistent elevation despite cabergoline:

Prolactin remaining >30 ng/mL on cabergoline 0.5 mg twice weekly warrants pituitary MRI to exclude prolactinoma as coincidental finding. The AAS-using population is not protected from incidental pituitary pathology; assuming all elevation is cycle-related delays diagnosis of treatable conditions.