Common (>10% users): None at therapeutic doses in clinical trials. Most-reported mild effects come in well under 10%.

Less common (1-10%):

• Headache (~3.3% in clinical trials; 1.6% in BSSM pooled data) — most common adverse event, usually transient.
• Nausea / GI upset (~2.1%)
• Hot flushes (~1.1-1.7%) — unusual for men, related to estrogen-receptor antagonism in thermoregulatory hypothalamus
• Mood changes / irritability (notably absent in enclomiphene group vs. 9.1% in clomiphene group in head-to-head data — removing zuclomiphene is the clinical reason)
• Libido changes (paradoxical — most see ↑libido as T rises, minority see ↓libido)
• Decreased energy (rare; occasionally reported)
• Acne (occasional, T-elevation-related)
• Muscle spasms (~0.9%)
• Weight gain (mixed — some report loss, some gain; reflects body-comp recomposition rather than fat gain)

Rare-serious (<1% but worth knowing):

• Visual disturbances — the signature side effect of clomiphene (blurred vision, scintillating scotomas, "shimmering"). With zuclomiphene removed, this is dramatically reduced but not zero. Reports exist; mechanism is thought to be SERM action on retinal estrogen receptors. Stop immediately if any visual change occurs, do not rechallenge.
• Gynecomastia — paradoxical at first glance, but rising T → rising aromatization → rising E2, which can transit through breast tissue at higher levels even with hypothalamic ER blocked. Less common than with TRT-monotherapy because total estrogen exposure is lower, but possible. Minor concern.
• Mood lability / depression — particularly in users with prior history of mood disorders. Less than clomiphene but possible.
• Polycythemia / hematocrit elevation — a risk wherever T rises (TRT included). Less concerning at enclomiphene's typical 600-700 ng/dL ceiling than at supraphysiologic TRT levels, but check CBC at baseline + 12 weeks.
• Hepatic enzyme elevation — clomiphene class has rare hepatotoxicity reports; enclomiphene-specific data is thinner. Check ALT/AST at baseline + 12 weeks.
• Pituitary effects with chronic use — theoretical, given chronic ER blockade at the hypothalamus / pituitary. No published cases of permanent dysregulation, but long-term human data >2-3 years is sparse.
• Theoretical: HPG-axis recalibration in young healthy men — no published evidence of permanent damage, but the proposition that you can chronically antagonize hypothalamic ERs in a young man with a normal axis and produce no long-term cost is untested. This is the most important archetype-specific concern.

Specific watch periods:

• First 4-6 weeks: Headache, mood changes, visual changes — stop on visual disturbance.
• Week 12 bloodwork: Re-check T, LH, FSH, E2, hematocrit, lipids, ALT/AST.
• Month 6+: Reassess whether continued use is justified or whether to cycle off.