Researchers recruited 20 members of the Brazilian military who claimed to be regular runners. They performed their test by giving some participants Ibuprofen and others a placebo, then had each individual perform rigorous exercise on a treadmill. This allowed researchers to draw conclusions about those taking Ibuprofen and those taking a placebo. After exhausting trials of exercise and running, it was discovered that those who took Ibuprofen before running reached exhaustion at a slightly higher rate than those who took the placebo. Researchers stated “these observations indicate that long-distance runners should take caution when using [nonsteroidal anti-inflammatory drugs such as ibuprofen] A Study in the Medicine & Science in Sports & Exercise in 2012 discovered that men who took ibuprofen before cycling had a greater rise in a blood marker that indicates increased intestinal permeability, compared to those who did not ingest ibuprofen before cycling. This basically means that toxins and other byproducts from bacteria may be able to enter into the bloodstream.  A study in 2006 found that marathon runners who took ibuprofen before exercising had higher levels of intestinal permeability and inflammation versus those who didn’t take ibuprofen. Gastrointestinal distress is not the only common side-effect that occurs while taking ibuprofen and exercising, other possible issues include: headaches, ulcers, and even renal complications.improve muscle-endurance performance because the side effects...may outweigh the expected benefits.”