The concept -- based on the (obsolete) Arndt-Schulz law -- that concentrations of potentially toxic substances below the amount that cause inhibition (toxicity) will cause stimulation. (It is well known that substances can have different effects at different concentrations, but they do not follow the general pattern proposed by homeopathy advocates.)

Controversial theory which argues that there is a benefit to health, or decrease in biological damage from radiation as dose in increased (valid only for very small doses).

Hormesis is the term for generally-favorable biological responses to low exposures to toxins and other stressors. A pollutant or toxin showing hormesis thus has the opposite effect in small doses than in large doses.