And run through fire I will for thy sweet sake.
Transparent Helena! Nature shows art,
That through thy bosom makes me see thy heart.
Where is Demetrius? O, how fit a word
Is that vile name to perish on my sword!
– William Shakespeare
A Midsummer Night’s Dream, Act 2, Scene 2. The love juice takes effect on Lysander immediately upon awakening and feasting his eyes on Helena. It’s love at first sight for him. He declares he will "run through fire" for Helena and threatens to kill Demetrius with his sword.