Ohio's state legislature has banned transgender medical procedures involving children and restricted transgender athletes on school sports teams, overriding the governor's veto.
The state's Republican Governor Mike DeWine had rejected the legislation, saying such decisions should be between families and medical providers.
But the Ohio Senate overrode his veto by 24-8 after the state House voted similarly this month by 65-28.
The ban will take effect in 90 days.
More than 20 Republican-led states now have laws restricting or banning transgender medical treatments involving children.
Ohio's legislation bans doctors from prescribing puberty blockers, hormone therapy or performing gender transition surgery on minors, which in the state is defined as being under 18.
The law - called House Bill 68 - requires mental health providers to get permission from at least one parent to diagnose and treat a gender-related condition in a child.
Medical providers who violate the bill could face disciplinary action from their licensing board.
A clause in the measure allows those already undergoing such transition to continue doing so, as long as doctors say stopping it would cause harm otherwise.
It also bans transgender athletes on girls' and women's sports teams from kindergarten (five-year-olds) through to 12th grade (17 to 18-year-olds) and collegiate level.
At Wednesday's hearing, Kristina Roegner, a Republican state senator, told fellow lawmakers "attempting to change someone's sex is a fool's errand".
William DeMora, a Democratic state senator, said the bill was "anti-science and hateful".
In December, Mr DeWine vetoed the bill, a rare move from a Republican governor in one of the most conservative-leaning states in America.
He said these decisions "should not be made by the state of Ohio", but by "the parents who have seen that child go through agony".
But Mr DeWine's fellow Republicans argued the measure was necessary to protect children and used their supermajority to override him.
Following conservative backlash over his veto, Mr DeWine offered what was interpreted as a compromise measure.
He issued an executive order banning gender-transition surgeries for children at some hospitals and clinics. Medical professionals say such operations are not happening in the state.
Opponents of the legislature's bill have suggested they will bring legal challenges as others have done in Arkansas, where a federal judge struck down a similar law saying it violated the due process rights of children and families.
