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“Magnesium citrate is used before colonoscopies to really get the bowel going,” said Dr. Li.

Decades ago, to prepare for a colonoscopy, patients first had to clean out their colons using laxatives such as castor oil or magnesium citrate, sometimes over several days.

Paul Adams, the senior science research editor at Cook’s Illustrated, has written about the stabilizing powers of sodium citrate, an ingredient found in processed cheeses like Velveeta.

Viagra, known generically as sildenafil citrate, was patented by the drugmaker Pfizer in the 1990s and was initially used as a treatment for chest pain related to the heart.

It started with a big surprise in 2003, when one colony evolved to eat citrate, a compound the other colonies couldn’t metabolize.