What type of interaction between two chemicals causes one chemical that is not toxic to become more toxic?

Potentiating effects

Explanation:

In medical field, Potentiating refers to the enhancement of potency or effect of any drug, chemical or treatment method.

In case of chemicals, potentiating effects are caused when one drug or chemical comes in contact with another drug and chemical and their combined pharmacologic effect is higher than the combined or individual response of each drug. For example - Pharmacologic effect of alcohol and sedative and diazepam potentiate the effect of alcohol.