Common (>10% of regular users):

• Mild sedation and motor slowing — dose-dependent
• Oral mucosa numbness (kavain) — diagnostic, not concerning
• Mild GI upset (nausea, soft stools) — usually with high doses or empty stomach
• Tolerance buildup with daily use (see Tolerance section)

Less common (1-10%):

• Headache, dizziness
• Transient mild LFT elevation (ALT, AST) — usually resolves on discontinuation
• "Kava dermopathy" — yellowish, dry, scaly skin patches with chronic heavy use; resolves on cessation; possibly riboflavin-mediated
• Visual disturbance (light sensitivity, blurred near vision) at high doses
• Mild apathy with prolonged daily use

Rare-serious (<1% but historically defining):

• Idiosyncratic hepatotoxicity — the case cluster that triggered the EU bans. Most cases occurred with ethanol or acetone extracts; many involved co-medication (acetaminophen, alcohol, anticonvulsants), prolonged daily use, or tudei cultivars. WHO 2007 review concluded hepatotoxicity risk is real but predominantly modifiable through extraction method and cultivar selection. Mechanism candidates include flavokavain B (cytotoxic chalcone enriched in solvent extracts; PMC2992378), depletion of glutathione (Whitton 2003), and CYP-mediated reactive metabolite formation.
• Acute hepatitis / fulminant liver failure — rare; ~100 case reports globally through the 2000s, several requiring transplantation. Causality not always clean (frequent co-medications), but the signal is real enough to keep kava on regulatory watch lists.
• Extrapyramidal reactions — rare case reports of dyskinesia, dystonia, parkinsonism (possibly via dopamine reuptake or chronic kavalactone interference with nigrostriatal signaling). Caution in users with Parkinson's history.
• Allergic / hypersensitivity — rash, photosensitivity.

Watch periods:

• First 2 weeks: allergic / hypersensitivity, baseline tolerability
• Week 4-8: dermopathy onset; LFT recheck
• Beyond 8 weeks: hepatotoxicity case-report density rises — washout recommended