How many drug overdoses are caused because of bad quality control that would be eliminated (or mostly eliminated) by legalization and regulation. IOW, how many

How many drug overdoses are caused because of bad quality control that would be eliminated (or mostly eliminated) by legalization and regulation. IOW, how many people overdose because they get a batch of 90% pure heroin when they are used to 25% pure? This probably would be solved if they were not getting the drugs illegally.