Due to synergism, combining two depressants can increase the effects to the equivalent of:

The concept of synergism refers to the phenomenon where the combined effect of two substances is greater than the sum of their individual effects. In the case of depressants, when two are combined, the resulting impact can be significantly amplified, potentially leading to effects akin to those of three or more depressants acting simultaneously.

This understanding is critical, especially when considering the risks associated with using multiple depressants, such as alcohol and prescription medications. The dangers arise because the combined depressant effects can lead to severe respiratory depression, decreased heart rate, and even loss of consciousness, which would not occur if either depressant were taken alone or even together in lesser amounts without synergism.

Therefore, when two depressants are taken together, the potential for increased impairment or danger is not simply additive but multiplicative, which is why the equivalent impact can be likened to that of three depressants.