Is it permissible to sell medicines and receive their price later after reaching an agreement with the suppliers, knowing that this is the common method of transactions?

A person selling what he does not own involves two scenarios: selling a specific item he does not possess, or selling something he cannot deliver.

As for medicines that have been received and entered warehouses or pharmacies, they become the exclusive property of the purchaser. The fact that the price is deferred does not affect this, as long as the items are not usurious. However, if the medicines are given for the purpose of distribution (consignment), then what is sold from them is considered a sale, and what is not sold is returned. This type of sale is impermissible.