California will become the first US state to ban a controversial form of psychotherapy aimed at making gay teenagers straight.
Governor Jerry Brown said he had signed a bill into law by Democratic senator Ted Lieu of Torrance, which Mr Lieu says will prevent children from being psychologically abused.
From January 1, the state will ban what is known as reparative or conversion therapy for minors.
Mr Brown said the therapies "have no basis in science or medicine and they will now be relegated to the dustbin of quackery".
Gay rights groups say the practice is dangerous because it can put youth at higher risk of depression and suicide.
Conservative religious groups and some Republicans argue that banning conversion therapy would hinder parents' right to provide psychological care for children experiencing gender confusion.