Table 1. Combinatory index values, recommended symbols and descriptions for classifying synergism or antagonism using the Chou-Talalay method.

Range of CI	Symbol	Description
<0.1	+++++	Very strong synergism
0.1–0.3	++++	Strong synergism
0.3–0.7	+++	Synergism
0.7–0.85	++	Moderate synergism
0.85–0.90	+	Slight synergism
0.90–1.10	±	Nearly additive
1.10–1.20	–	Slight antagonism
1.20–1.45	––	Moderate antagonism
1.45–3.3	–––	Antagonism
3.3–10	––––	Strong antagonism
>10	–––––	Very strong antagonism

The more broadly defined criteria suggest that the combination index, CI < 1, = 1, and > 1 indicate synergism, additive effect and antagonism, respectively (Source: CalcuSyn manual, Biosoft, 2006).