Hospitals failing to pay drug bills and parallel trading by wholesalers and pharmacists are the main reasons for supplies being withheld.
Major pharmaceutical companies that have admitted halting shipments of some products include Pfizer, Roche and Sanofi.
Medicines for arthritis, hepatitis C and hypertension, statins, antibiotics, anaesthetics, antipsychotics and antidepressants are all affected.
Dimitris Karageorgiou, Secretary General of the Panhellenic Pharmaceutical Association, said: “I would say supplies are down by 90%. The companies are ensuring that they come in dribs and drabs to avoid prosecution. Everyone is really frightened.
“The government is panic-stricken and the multinationals only think about themselves and the issue of parallel trade because wholesalers can legally sell them to other European nations at a higher price.”
According to the Greek government, more than 50 companies are holding back products or planning to do so. The Ministry of Health is intending to fine eight major drug companies, which have not been named.
There are reports of widespread panic and anger among patients who are going from one pharmacy to another with prescriptions. “We have reached a tragic point,” commented Karageorgiou.
With austerity tightening in Greece, the debts owed to pharma companies by hospitals and social insurance funds has reached €1.9bn (£1.6bn).
Pfizer has admitted withdrawing four medicines “because alternatives were available and because of the parallel trade situation”: leukaemia drugs Zavedos and Aracytin, the analgesic Neurontin and the epilepsy treatment Epanutin.
Roche said it was withholding supplies to Greek public hospitals, apart from “critical medicines” such as HIV drugs, but was still supplying pharmacies.
Sanofi claimed it was still supplying public hospitals with life-saving and unique products (for which no generic version or recommended alternative exists).
GSK, AstraZeneca, Novartis and Boehringer Ingelheim denied they had stopped supply of any products to Greece.
The pharmaceutical industry has urged the Greek government to set its drug prices in accordance with a eurozone standard. Greek drug prices are 20% lower than the next lowest in the EU, giving rise to widespread parallel trading.
Greek regulator the National Organisation for Medicines has banned the export of 60 medicines and is considering another 300. It will fine wholesalers and pharmacists who have broken the export ban.