Final answer:
The claim that the additive factor is the least dangerous aspect of multiple depressant use is false, as it leads to a compounded and potentially life-threatening effect on the user.
Step-by-step explanation:
The statement that the least dangerous aspect of multiple depressant use is the additive factor is false. When multiple depressants are used simultaneously, their effects on the central nervous system can be potentially life-threatening, leading to complications such as respiratory depression, coma, or death. The additive effect, also known as synergism, means that the depressants' effects are compounded, which is indeed a highly dangerous aspect of polydrug abuse.