Britney Spears Amped Up on Caffeine, Coffee, Red Bull, Celsius

Britney Spears drinks caffeine drinks by the gallon, something experts say is not great but unsurprising for people with mental illnesses.

Sources with direct knowledge tell TMZ, which has produced a documentary that will air Monday, Britney guzzles Red Bull, Celsius, coffee, and dandelion tea almost nonstop. We're told she consumes so much caffeine, she'll sometimes stay awake for 3 consecutive days.

Experts, including Dr. Drew, tell TMZ, people with mental illnesses crave the high from these drinks, but it's not particularly healthy.

The documentary -- "TMZ Investigates: Britney Spears: The Price of Freedom" -- chronicles her life in the last 1 1/2 years since the conservatorship ended. The documentary details her relationships with her family, husband, and kids, in addition to other struggles that have caused concern among those closest to her.

The documentary reveals some of the recommendations people who were caring for Britney made at the end of the conservatorship.  One of the recommendations -- keep knives away from her.