It depends on the degree to which you consider maliciousness or incompetence murder. For example, the Republican government in the United States has been working for years to slash health care funding and benefits for people they don't think deserve to live. Is that murder? I'd say so, in which case democide is fair to use as a term.
"Democide," the murder of citizens by their own government, constitutes the leading cause of natural death globally. A government is capable of carrying out killing of citizens on a massive scale when compared with murder or accident, which on would imagine must be other leading causes of unnatural death. Scale alone makes democide the leader.
Without a thorough examination of all the types of unnatural deaths, it is not possible to say that governments are responsible for this. A myriad of health and environmental causes can bring about an unnatural death. To find a correlation, one would have to check if the dead person had any ties to the government. Even then, all this seems like a waste of resources to find information about a phenomenon that has a minimal chance of being true.
While democide is a big problem, it is not the leading cause of death. Is something categorized as democide when it is the result of internal civil war? It depends on how to define the cause of death. In most places, speeding in a motor vehicle and suicide are far bigger causes of death.