The affix aṇ comes after oṣadhi when it does not mean a species.,
Thus औषधं पिबति \he drinks medicine\. औषधं ददाति \he gives medicines\. Why do we say \when not meaning a जाति or species\. Observe, औषधयः क्षेत्र रूढा भवन्ति 'the herbs are growing in the field.',