The gf who is the regional North Thailand sales rep works for a pharmaceutical company & insists this is # 1 in Chiang Mai.
And they certainly seemed to stock everything the day I was there.
Location: 251/3-4 Kaew Nawarat Road. The road that goes past McCormick hospital. Dara Bhasaj is on the left hand side going out of town, towards the super highway. 100 metres before the super highway.
GPS: N18.80005 E99.01274