noun
additive effect
Technical term used in pharmacology, statistics, and other scientific fields to describe a combined effect equal to the sum of individual effects.
この二つの薬には相加効果が認められた。
An additive effect was observed between these two drugs.
相加効果と相乗効果の違いを説明してください。
Please explain the difference between additive effect and synergistic effect.
相乗効果 (synergistic effect) means the combined effect is greater than the sum of individual effects, while 相加効果 is simply the sum.
Compound of 相加 (sōka, 'addition, adding together') and 効果 (kōka, 'effect'). The term is a direct calque from English 'additive effect'.