They said sick people are frequently being turned away without drugs.
Chemists also report at least once a day they are unable to dispense prescriptions, the National Pharmacy Association said.
They want the government to grant greater flexibility for pharmacists to substitute medication safely.
At the moment, patients must go back to their GP for a new prescription in most cases if the item or dose prescribed is out of stock.
In January, Lancashire coroner Christopher Long wrote to Health Secretary Wes Streeting after the death of two-year-old Ava Hodgkinson, from Banks, near Southport, in 2022.
She died of sepsis after delays in receiving antibiotics due to rules preventing a chemist from amending an out-of-stock prescription.
It said a survey of 500 pharmacies found 96% could not fulfil a prescription at least once a ...