What is an additive drug interaction?

• A. Two drugs with similar effects increase each other’s effects, raising adverse effects.
• B. When one drug blocks another's effect.
• C. Drugs cancel each other out.
• D. When drugs have no interaction.

Answer: (A)

Additive drug interaction happens when two medications have similar effects and their combined impact equals the sum of what each would produce alone. Because both drugs contribute to the same response, the total effect can rise, and any adverse effects can compound as a result. The described scenario fits this idea: two drugs with similar effects add up, increasing the overall effect and the potential for adverse effects. This differs from antagonism, where one drug blocks or dampens another, or from no interaction, where the drugs don’t influence each other. It’s also distinct from synergy, where the combined effect exceeds the simple sum.