Company Names, addresses, dates:
  Purcellville Pharmacy (N. Guy Miller Proprietor), 107 W. Main Street, Purcellville VA
  Purcellville Pharmacy (N. Guy Miller Proprietor), 21st Street, Purcellville VA
  Edwards Purcellville Pharmacy, Purcellville VA (ca.1969-1970) ¹

Notes:
Nelson Guy Miller (1877-1941)² was the proprietor of the Purcellville Pharmacy, as early as 1908.³

The book "Images of America - Purcellville" shows a 1908 photo of the Purcellville Pharmacy on page 43. Based on the map on page 79, that places the location of the drug store at 107 W Main Street. There was a fire in 1914, and presumably the Pharmacy was one of the buildings that burned down. The pharmacy appeared to be made of wood in the 1908 photo, but a photo on page 83 shows the brick building in the same location.⁴
There is also a 1935 photo of the Purcellville pharmacy at 21st Street. So presumably it moved to that location sometime after the fire.⁴

Miller passed away in 1941².
William Waverly Friend (1868-1948)⁵ took over as the proprietor. Friend was previously the proprietor of the W.W. Friend drugstore in Manchester VA.⁶

I couldn't determine what year the Purcellville Pharmacy closed. I did find newspaper mentions referring to the "Edwards Purcellville Pharmacy" as late as 1970.¹
I'm not sure but I think the store may have been owned by Thomas or William Edwards, who were affilliated with the Edwards Drugstore in nearby Leesburg VA.

	This is a clear, 3.5" machine-made unembossed bottle with a cork and a label: label (printed): Purcellville Pharmacy / N. GUY MILLER, PROP. / PURCELLVILLE, VA. label (hand-written): Date: 9-27-35 / Fifteen drops in a bottle water 3 times a day Dr. Hackey
	This is a clear, 3.3" machine-made unembossed bottle with a plastic screw-top and a label: label: SWEET OIL / Purcellville Pharmacy / N. GUY MILLER, PROP. / PURCELLVILLE, VA.