How long does it take for a fiber laxative to work?
                                
                                
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                                    4 min read                                
                            
                                According to the National Institutes of Health, fiber-based laxatives, also known as bulk-forming laxatives, are among the gentlest options for treating constipation. Many people wonder, "how long does it take for a fiber laxative to work?" The onset of action can range from 12 hours to as long as 72 hours, depending on individual factors.