Additive: Effect of substance A and B together is equal to the sum of their individual effects- Example: Aspirin and acetaminophen

Permissive: Presence of substance A is required for the full effects of substance B- Example: Cortisol on catecholamine responsiveness

Synergistic: Effect of substance A and B together is greater than sum of their individual effects- Example: Clopidogrel with aspirin

Tachyphylactic: Acute decrease in response to a drug after initial/repeated administration- Example: Nitrates, niacin, phenylephrine, LSD, MDMA