LOS ANGELES >> As awareness grows around the dangers of head trauma in sports, a small number of professional fighters and football players are turning to a psychedelic called ibogaine for treatment.

Ibogaine, which is derived from a West African shrub, is a Schedule 1 drug in America with no legal medical uses, and experts urge caution because of the need for further studies. But the results, several athletes say, are “game-changing.”

“It saved my ...