Scary Warning If Your Butt Is Too Big If there is too much fat in your buttocks, it could become a major health concern. HealthDay News reports that medicine--from painkillers to vaccines and contraceptives to anti-nausea drugs--injected into large posteriors very often do not reach the bloodstream. Researchers at The Adelaide and Meath Hospital in Dublin, Ireland say the problem is particularly evident in women. "We are the first to report that the majority of intramuscular injections into the buttocks are not effective in the Western adult population," lead researcher Victoria O. Chan told HealthDay News. The study: Researchers evaluated 50 men and women ages 21 to 87, all of whom were scheduled for CT scans. Each received medicine by an injection in the buttocks that contained a milliliter of air. The CT scan established the location of the air bubble and the medicine so the team could tell if the medicine landed in the gluteal muscles where it could be absorbed or got stuck in the fat where it couldn't. The results: Only 32 percent of the injected medications actually made it to the muscles, and shots missed their mark far more frequently in women than in men, reports HealthDay News. Fifty-six percent of the shots given to men reached the muscles, but only 8 percent of those given to women did. In only two of the 25 women who received injections did the medicine hit the mark. So how much buttocks fat is too much fat? Chan said it is tough to know. "A best estimate of fat thickness can be made by depressing the upper outer quadrant of the buttock. Bearing in mind that the length of the needle used is approximately 3 centimeters (1.18 inch) it follows that the more obese the patient, the less likely the needle will reach the muscle underneath the fat," she explained to HealthDay News. A longer needle may be needed for those who have fatter buttocks. Also, be proactive! If you're given medicine through a shot in the butt and you don't think it's working, speak up. The findings were presented at the annual meeting of the Radiological Society of North America in Chicago.