Which statement best describes additive effects across glaucoma drug classes?

• A. Additive effects occur only within the same class
• B. Additive effects occur across different classes
• C. There are never additive effects
• D. Additive effects depend on the drug's color

Answer: (B)

Additive effects come from using drugs that work through different mechanisms to lower intraocular pressure. When you combine a medication that reduces aqueous production with one that increases outflow, their effects add up, giving a greater overall IOP reduction than either would alone. This cross-class combination is common because each class targets a different part of aqueous humor dynamics, so the total effect sums rather than overlaps redundantly. Colors or other unrelated factors don’t influence this; what matters is using distinct mechanisms to achieve a larger drop in pressure.