Patients claiming free prescriptions in England face checks before medicine is issued in an effort to stamp out fraud.
Prescription fraud currently costs the NHS in England an estimated £256m a year.
A new digitised system to be piloted next year will mean pharmacies can instantly verify who is entitled to free medication.
But pharmacists have opposed similar plans in the past, saying they harm patient trust.
Sandra Gidley from the Royal Pharmaceutical Society, said: "What if the computer says no? That is a real dilemma.
"Sometimes somebody has free prescriptions legitimately, they've got a medical exception – they're something like a diabetic – and they might forget to renew it and the computer says no.
"You're not going to stop a diabetic from getting their insulin, for example.
"So I think this is potentially fraught with problems."
'No easy target'
Currently, patients either present an exemption certificate or sign the back of their prescription stating they do not have to pay the £8.80 charge.
The NHS Business Authority runs random checks, but only after the medication has been dispensed.
In 2016-17, the number of £100 fines it issued for false claims doubled to more than 900,000.
The new approach will require pharmacists to check the digital exemption system before handing over medication.
Health and Social Care Secretary Matt Hancock said: "The message is clear. The NHS is no longer an easy target and if you try to steal from it you will face the consequences."
England is the only part of the UK which charges for prescriptions.
The Royal Pharmaceutical Society and the British Medical Association have said many of those fined are not fraudsters, but people who fail to complete paperwork properly or forget to renew their exemption.
People with long-term illnesses and those on low incomes were most likely to be affected, they said.
Fraud is estimated to cost the NHS £1.2bn a year, or about 1% of its total budget.
The prescription checks are part of a series of measures intended to prevent £300m of fraud by April 2020.
Other measures include a counter-fraud team targeting rogue dentists and pharmacists who charge the NHS for work they have not carried out.