After loud backlash from players, the NFL players’ association clarified in its own memo that the league hasn’t banned the use of smelling salts — it has only banned teams from being the suppliers.

The NFL sent a memo to teams Tuesday banning all forms of ammonia inhalants and smelling salts from games, pregame activities and halftime, following an FDA warning about their unproven safety and efficacy.

On Tuesday, the NFL sent a memo to clubs saying they are no longer allowed to provide the substance to players, citing safety concerns. Here's what experts say about the effects and the risks.