Tranquillizer darts are not generally included in military or police less-than-lethal arsenals because no drug is yet known that would be quickly and reliably effective on humans without the risks of side effects or an overdose. This means that effective use requires an estimate of the weight of the target to be able to determine how many darts (if any) can be used. Shooting too few would result in partial effects only, while too many can kill the target. According to James Butts, former Chief of Police of Santa Monica, "Tranquilizing agents don't affect everyone uniformly. Therefore you cannot predict whether or not you have a sufficient dose to tranquilize the individual. Second, any tranquillizer will take time to enter the bloodstream and sedate the individual. If someone is advancing on you with a deadly weapon or a threatening object, there's no way a tranquillizer would take effect in the two to three seconds it would take someone to seriously injure you