Why is weed legal some places and not others?

Legalization of marijuana for adult recreational use and for medicinal purposes is currently the subject of much public debate. For the last few years, the Department of Justice has said that it is not going to prioritize enforcement of federal marijuana laws when state laws allow for possession of small amounts of marijuana. They are giving states the flexibility to test new policies for both ‘medical’ and recreational use of marijuana. Whatever happens, public health experts are worried that these changing policies could lead to more use among teens. Regular marijuana use as a teen may harm the developing brain – making learning and memory worse – and can impair the ability to drive safely (especially when combined with alcohol).