I recommand SynergyFinder: https://synergyfinder.fimm.fi/
You can follow the tutorial just on the homepage.
(From user guide)
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The summary synergy scores can be interpreted as the average excess response due to drug interactions (i.e. synergy score of 15 corresponds to 15% of response beyond expectation). There is no particular threshold to define a good synergy score, since combination synergy is highly context-specific. However, based on our experience, the synergy scores near 0 gives limited confidence on synergy or antagonism. So when synergy score:
Less than -10: the interaction between two drugs is likely to be antagonistic;
From -10 to 10: the interaction between two drugs is likely to be additive;
Larger than 10: the interaction between two drugs is likely to be synergistic.