Patients in England are suffering from shortages of some medicines, according to the All Party Pharmacy Group of MPs.
Their report says part of the problem is drugs being bought cheaply in the UK then sold at higher prices elsewhere in Europe.
The MPs say the government needs to "up its game" to tackle the acute and disproportionate impact on patients.
The Department of Health says it has issued new guidelines and is working with every part of the supply chain.
The report is the result of an investigation by MPs into shortages of some prescription medicines which have caused difficulties for the NHS for the last four years.
At any one time between 30 and 40 medicines are in short supply. These have included treatments for Parkinson's disease, some cancers and depression.
The All Party Pharmacy Group of MPs says the main cause is some medicines being exported by smaller wholesalers to make a profit, not the supply from pharmaceutical manufacturers.
Kevin Barron, Labour MP and chairman of the group, told the BBC: "We understand they're manufacturing 20% to 30% over and above what UK patients need. But sadly UK patients aren't getting the drugs in a timely fashion before they're sent abroad and that's the issue. "
It is entirely legal for anyone with a licence to trade in medicines to buy them in the UK and and sell them abroad.
The British Association of Pharmaceutical Wholesalers represents the nine big companies that supply 85% of the UK's medicines.
Martin Sawer, director of the BAPW, says while these large companies trade within the UK there are about 1,700 other licence holders, and a few take advantage of buying relatively cheaply here and selling where prices are higher.
"It varies from medicine to medicine but in Germany which is the highest priced market in the EU, some medicines can be nearly twice as much as in the UK," he said.
The MPs said they had heard of cases involving vulnerable patients not receiving the medicines they needed, including the case of a pregnant woman who had to wait for five days for drugs essential to preventing her having a miscarriage.
Tougher action call
The Patients Association, which gave extensive evidence to the MPs' inquiry, said: "The government needs to investigate this problem as a matter of urgency, using the findings of this report as a starting point."
The report calls on the government to consider whether it could legally restrict the export of medicines on the grounds of protecting public health. Similar measures are said to be under discussion in France.
The report says none of the measures put in place by the government so far has made any significant difference.
The government has paid pharmacists in England an extra £12m a year in recognition of the extra time they are having to put into sourcing medicines.
Lloydspharmacy, which has campaigned on the issue, called for the government to recognise the scale and seriousness of the problem, and act on the MPs' recommendations.
Ronan Brett said: "Our pharmacists have made it clear to us that they are finding it increasingly difficult to get hold of standard, widely prescribed medicines; 80% have been unable to dispense items for four or more prescriptions a week."
The Pharmaceutical Services Negotiating Committee, Pharmacy Voice and the Royal Pharmaceutical Society backed the call for tougher action in a statement.
"The evidence compiled by the APPG reinforces the views of all pharmacy bodies, that delays to the supply of medicines to patients cause distress, risk patient harm and are unacceptable. Pharmacists across the UK consistently work hard to ensure medicines reach patients promptly."
The Department of Health in England said it would consider the report carefully. A spokesman said that work was going on behind the scenes to ensure contingency supplies were available.
"We have well established arrangements for dealing with supply issues, to minimise any potential impact on patients. Much of this work goes unseen, as difficulties are prevented before they happen," he added.