Yes Walmart Gift cards can be used at the Walmart Pharmacy at any Walmart store.
A Walmart Gift card acts just like a regular debit card but can only be used for purchases at Walmart Stores or any other Walmart owned places.
You can also use the Walmart Gift Card online at Walmart.com but not at any other websites.
If you want to use the Walmart Gift Card to pay for medicine at the Pharmacy at Walmart you can do so because the Walmart Gift Card will be accepted as I've seen a few people using their Walmart Gift card at Walmart Pharmacy.
I've never used a Walmart Gift Card at the Walmart Pharmacy but I did see a few people using the Walmart Gift Card at Walmart Pharmacy and they had no trouble using it as long as you have the money in the card.