Which term would you use to describe the effect of a combination of a phenothiazine tranquilizer and an anesthetic?

Additive

Explanation:

When a  tranquilizer  is used along with an anesthetic agent, it enhances the effect of anesthesia and hence it must be given in small quantity to produce the same effect as that of an surgical anesthesia. Phenothiazines do not have the analgesic characteristics hence they are usually associated with analgesic substances to produce therapeutic effect. In common cases it is given along with respiratory depression to produce additive effects

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