This is the 3140th most frequent Russian word.
лекарственных
"Medicinal" or "of medicines."
The word 'лекарственных' modifies 'препаратов' to describe medicinal drugs, focusing on their pharmaceutical qualities.
Я изучаю свойства лекарственных препаратов.
I study the properties of medicinal drugs.
Here, 'лекарственных' describes 'растений,' indicating plants used for medical purposes.
Производство лекарственных растений требует особого ухода.
The cultivation of medicinal plants requires special care.
In this case, 'лекарственных' qualifies 'трав,' referring to medicinal herbs used traditionally.