The arson attack took place at Heath Pharmacy in the early hours of Friday morning (Jan 3).
At around 2.25am, officers were called by the Fire Service to a report of a blaze at the premise on Free School Lane, Halifax.
Two suspects approached the building and smashed a front window before setting fire to the inside.
They then returned to a vehicle, which had been parked on Clover Hill Road, and made off along Free School Lane in the direction of Halifax, police said.
Nobody was injured in the attack, police confirmed.
The pharmacy has been on the premises since 1895, manager Amanda Smith said.
She described the moment the assailants petrol-bombed the front of the pharmacy.
Amanda said: "They smashed a glass panel and threw two petrol bombs inside.
"Luckily we have quite a large floor mat and it soaked up most of the petrol and stopped it spreading further so the fire was concentrated in a small area.
"We will need to replace the shop floor and some of the fixtures and fittings.
"The main problem is the amount of soot covering everything."
Amanda said staff had received a lot of support from customers since the attack.
She added: "We have been overwhelmed by the messages of support from our customers.
"Our staff all came in early to clean and ensure we could open as usual at 9am."
Detectives are appealing for anyone with information or anyone who witnessed a dark-coloured saloon vehicle driving in the area to contact police.
Anyone who witnessed any suspicious activity in the hours leading up to the incident is also asked to contact officers.
Information can be passed to Calderdale CID on 101, quoting crime reference 13200003109.
Amanda added: "Community pharmacies are really struggling at the moment due to reduced funding and this is a problem we could do without.
"Pharmacies provide a vital health service to their local communities and we were determined to make sure we continued to provide that service and ensure no one went without medication.
"I am so proud of our team who have once again shown their resilience and dedication to their community."