Cabergoline

Cabergoline (Dostinex, Cabaser) is a long-acting D2 dopamine receptor agonist used clinically for hyperprolactinaemia, prolactin-secreting pituitary adenomas, and Parkinson’s disease. In AAS protocol design, cabergoline is the standard intervention for prolactin elevation on 19-nor compound cycles (nandrolone, trenbolone) and for symptomatic prolactin-driven libido loss with normal testosterone.

Mechanism — D2 dopamine receptor agonism:

Dopamine from hypothalamic tuberoinfundibular neurons exerts tonic inhibition on pituitary lactotroph cells via D2 receptor binding. The signal continuously suppresses prolactin secretion; loss of dopamine signal produces hyperprolactinaemia by disinhibition. Cabergoline binds the D2 receptor with high affinity and dissociates slowly, producing sustained lactotroph suppression that lasts well beyond the drug’s serum residency.

The long receptor dwell time produces the characteristic long-half-life pharmacological effect — cabergoline’s serum half-life is approximately 65 hours, but the prolactin suppression effect persists 2–3 weeks after a single dose. This pharmacology supports the standard twice-weekly dosing schedule that other dopamine agonists (bromocriptine, requiring 2–3 daily doses) cannot match.

Pharmacokinetics:

– Elimination half-life: ~65 hours
– Pharmacological effect duration: 2–3 weeks per dose
– Standard cadence: twice weekly (Monday/Thursday or equivalent)
– Metabolism: primarily hepatic; renal excretion of metabolites

Dosing protocol:

Reactive use (prolactin elevation confirmed on bloodwork):

– Starting dose: 0.25 mg twice weekly
– Titration: increase to 0.5 mg twice weekly if prolactin remains >20 ng/mL after 4 weeks
– Maintenance: continue throughout 19-nor exposure, taper over 2 weeks at cycle end

Prophylactic use on extended 19-nor cycles:

– 0.25 mg twice weekly throughout cycle
– Bloodwork at week 4 and week 8 to verify prolactin within reference range
– Lower threshold for intervention than user-reported symptoms — “deca dick” is reliably preventable with adequate dosing

Endocrine Society guideline reference:

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 (faster prolactin normalisation, higher rate of microadenoma reduction) and tolerability (lower rate of nausea, postural hypotension, headache).

Side-effect profile:

– Nausea: the most common side effect, particularly at protocol initiation. Mitigation: take with food, start at 0.25 mg twice weekly, titrate gradually. Resolves within 2–3 weeks for most users.
– Headache: 10–20% of users; usually transient.
– Postural hypotension: related to dopaminergic vasodilation. Manageable with hydration and gradual position changes.
– Sleep effects: some users report vivid dreams or mild sleep disruption.
– Gambling and impulse control changes: documented at high doses in Parkinson’s disease populations through D3 receptor effects. Not commonly reported at AAS-protocol dosing but worth awareness.

Cardiac valvulopathy concern — dose-dependent:

Cabergoline at supraphysiological doses (Parkinson’s range, 4+ mg/day) carries documented cardiac valvulopathy risk through 5-HT2B serotonin receptor activation. The mechanism produces fibrotic changes in heart valve tissue analogous to ergot-derivative cardiac effects.

The AAS-relevant dose range (0.25–1 mg/week, total weekly dose 4–10× lower than the Parkinson’s threshold) is well below the valvulopathy concern threshold. Long-term cardiac monitoring is not routinely indicated at AAS-protocol dosing. Annual echocardiogram is reasonable for users on continuous cabergoline beyond 2 years at higher cycle-related doses (0.5 mg twice weekly chronic).

Drug interactions:

– Antipsychotics and antiemetics with central D2 antagonism: pharmacologically opposed; concurrent use defeats the cabergoline mechanism
– CYP3A4 inhibitors (clarithromycin, ketoconazole): may elevate cabergoline serum concentration
– Dopaminergic medications (other agonists, levodopa): additive effects

Monitoring on protocol:

Prolactin bloodwork at week 4 of cabergoline initiation, then every 8 weeks during chronic use. Target serum prolactin: within reference range, typically <15 ng/mL. Persistent elevation despite cabergoline 0.5 mg twice weekly warrants pituitary MRI to exclude prolactinoma as coincidental finding.