Patients struggle to obtain drugs for life-threatening conditions in 80 per cent of NHS trusts in England and Wales, a survey suggests.
Delays are reported in four out of five trusts because medicines intended for NHS patients are exported to other EU countries, causing shortages.
Quotas have been introduced to control the amount of drugs set aside for the NHS but this has been found to exacerbate the problem.
Labour MP Huw Irranca-Davies is calling for action from both the government and industry, after more than 60 health authorities responded to his freedom of information request about drug shortages.
The Department of Health said it is considering an investigation into the scale of the problem.
A spokesman said: “It is for manufacturers to ensure that any quotas set are flexible enough to cope with reasonable fluctuations in demand. Where quotas are used, companies setting them should also make sure that they are set fairly.
“Manufacturers should have their own contingency arrangements in place for pharmacies to be able to obtain medicines directly if they have problems getting hold of them.
“The government does maintain a buffer stock of certain essential medicines that can be released in emergencies. We will take any action necessary in the event of disruption to supply and distribution of medicines that causes serious risk to patients.”
In April health minister Simon Burns told Parliament that the department is considering a one-off survey of shortages of medicines at local pharmacies.
Last month MPs in the All-Party Pharmacy Group published a report on their inquiry into medicine shortages, which found that the problem is caused principally by the export of medicines intended for NHS patients to other EU countries. The practice is legal under European provisions for the free movement of goods.
The shortages are worsened by attempts by those in the supply chain to solve the problem through quotas and other alternative supply mechanisms, the report said.
Pharmacists then spend long periods of time sourcing medicines in short supply, meaning they have less time to spend with patients.
And patients were found to be suffering as a result of the shortages, with the group citing examples where those with serious conditions such as epilepsy, schizophrenia and diabetes are unable to get crucial medicines when they need them.