Zac Efron appeared on the series premiere of Running Wild with Bear Grylls last night, and while he had no trouble snacking down on an omelet of worms and wild bird eggs, Efron's most surprising moment came when he opened up to Grylls about his struggles with substance abuse.

When Zan and Bear were lounging fireside after their day's adventure, the topic of Efron's rehab stint came up, and the Neighbors actor discussed that dark period in his life with surprising candor.

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