Asda has lost its appeal to open a controversial pharmacy at its Penryn store.
The company appealed against Cornwall Council's refusal to lift a condition to enable it to have a pharmacy counter.
That condition was attached to its 2008 planning permission to add a mezzanine floor to the supermarket.
The Council ruled it would be detrimental to the town centre as it could cause the pharmacy in Market Street to close if it went ahead.
This is part-operated by Hendra and Penryn Surgery and they said sales had already fallen since Asda opened and just a further 10 per cent reduction would leave the firm operating at a loss.
In December Asda put a portable building in the car park and began running a counter without permission, but no planning enforcement action was taken as the council wanted to wait for the outcome of the appeal.
A petition with more than 850 names was submitted against the scheme.
Planning inspector JM Trask dismissed the appeal this week.
He said: "It is likely it would result in a reduction in trade at the town centre pharmacy, which would be likely to prejudice its viability.
"The town centre is fragile and the loss of one of the few core businesses would have a significant adverse impact on the vitality and viability of Penryn."