How to say "complicate" in Japanese

• こじらせる
  ichidan verb, transitive verbCovers 'complicate' as 'make worse': aggravating a situation, dispute or relationship so that it deteriorates into a tangle. A less common verb, usually written in kana; the nuance is worsening, not adding complexity.
  彼かれは病気びょうきをこじらせてしまった。↗

  He is suffering from an aggravated disease.
• こじらす
  godan verbA close variant of こじらせる with the same aggravate-and-complicate sense; commonly used of a disease or illness made worse, otherwise of situations that sour. Usually written in kana.
• こね回すこねまわす
  godan verb, transitive verbLiterally to knead and mix; its 'complicate' sense is really 'turn into a mess' by stirring. For abstract complications — a plan, an issue — it is seldom the word you want.
• こね返すこねかえす
  godan verb, transitive verbA near-twin of こね回す: kneading and mixing, hence figuratively churning something into a mess. Like it, this is marginal for the ordinary sense of 'complicate' and mainly a messing-things-up word.

Use the こじ- verbs when something is made worse — an illness, a dispute, a relationship — rather than merely more complex; the こね- verbs literally mean kneading and mixing, fitting 'complicate' only as 'turn into a mess'.

Usage comparisons are AI-assisted and cross-checked by multiple models; for study reference only

• こじらせるto aggravate
• こじらすto make worse (e.g. disease)
• こね回すこねまわすto knead
• こね返すこねかえすto knead