Gov. Gavin Newsom signed a bill that prohibits social media platforms from providing addictive features to users under 16, the first law of its kind in the nation.

European Union authorities said the company’s use of “addictive design” violated a digital safety law.

With support from Markwayne Mullin and Robert F. Kennedy Jr., the kratom industry is pursuing a potentially lucrative policy. Mr. Mullin owns equity in a company that could benefit.