Researchers concluded that spice users have an increased risk of overdose — First, synthetic cannabinoids act on the same central cannabinoid receptors in the brain as THC in natural cannabis, but have a greater ability to bind with these receptors and are far more likely to spark a physiological reaction when the two meet. Second, the inability to control the concentration and potency of the drug when smoked created a greater chance of overdose. Another common overdose factor stems from the “other ingredients” mixed with spice —- including rat poison.