The concentration of a substance determines its effects. In the example above the substance causes only the side-effect of 'fatigue', the 'Calms Acid reflux' effect is not active as the concentration is too low.
The concentration of a solution or ingredient causes different side effects to become active. It is a core-element in producing drugs in Big Pharma.
Machines can be used to alter the concentration of a substance to make a desired effect active or an unwanted side-effect inactive. Often it is not possible to have a substance without active side-effects due to overlapping active areas of the effects. It is possible to create drugs with multiple good effects, e.g. by using a Multimixer.