The Food and Drug Administration (FDA) was created when Congress passed the Food and Drugs Act in 1906. This act was the first of a series of laws and amendments that gave the FDA jurisdiction over the regulation of foods and patent medicines. In 1938, Congress strengthened and expanded the FDA, to include the regulation of therapeutic and medical devices within its jurisdiction.

The FDA's Bureau of Medical Devices and Diagnostic Products was created in 1974, and soon operated in conjunction with the Medical Devices Amendments of 1976. The amendments helped to clarify the logistics of the regulation of medical devices, and required the FDA to "ensure their safety and effectiveness."

Radiation had been recognized as a health hazard since before World War I, and the FDA monitored the health risks that radiation emitting products posed to America's workers and consumers. As FDA's responsibilities for monitoring radiological devices grew, a bureau within the FDA called the Center for Devices and Radiological Health (CDRH) was established.

In 1980 the FDA's budget had swelled to over $320 million, with a staff of over 7,000. Many bureaus controlled areas such as biological drugs, consumer products, public health standards, and veterinary medicines.

FDA approved medical devices before they "went to market." This was called Pre-Market Approval and was a somewhat complex process. In the FDA Pre-market Approval scheme, devices were organized into three classes, as established by the 1976 Medical Device Amendments.

1. Class I devices, "general controls provide reasonable assurance of safety and effectiveness," for example bedpans and tongue depressors
2. Class II devices, such as syringes and hearing aids, "require performance standards in addition to general controls"
3. Class III devices like heart valves and pacemakers are required to undergo pre-market approval as well as complying with general controls

In addition to classifying devices as Class I, II, or III, FDA approved devices for market in one of two ways:

1. Proof of Pre-market Equivalence to another device on the market, termed 501(k)
2. OR Pre-market Approval (Rigorous Testing)

If a company could show Pre-market Equivalence (proof that a new product was equivalent to one already on the market), the new product could be approved by FDA without extensive, costly, rigorous testing. In 1984 about 94% of medical devices came to market through Pre-market Equivalence.

If a product was not equivalent to one that was already on the market, FDA required that the product go through testing to gain Pre-market Approval. In 1984 only about 6% of medical devices were required to go through this testing.

Thus, it was clearly in the interest of medical device producers to show that their product had pre-market equivalence. The Therac-25, brought to market in 1983, was classified as a Class II medical device. Since Canadian Medical Company (AECL), designed the Therac-25 software based on software used in the earlier Therac-20 and Therac-6 models, Therac-25 was approved by FDA under Pre-market Equivalency.

A 1983 General Accounting Office (GAO) report criticized the FDA’s "adverse experience warning system" as inadequate. FDA had published reports about potential hazards, including reports in their own newsletter, The FDA Consumer. The FDA implemented the mandatory medical-device reporting rule after Congress passed the Medical Device Reporting Legislation in 1984. This rule required manufacturers to report injuries and problems that could cause injuries or death.

Before 1986, users of medical devices (hospitals, doctors, independent facilities) were not required to report problems with medical devices. Instead, under the medical device reporting rule, manufacturers of these devices were required to report problems. The idea was that manufacturers would be the first to hear about any problems with the devices they made and that therefore reports would be timely. In addition, manufacturers would be most likely to have the correct information needed about a device to help resolve difficulties.

In the mid-1980s, the FDA’s main enforcement tools for medical devices already on the market were publicity. The FDA could not force a recall, it could only recommend one. The CDRH (Center for Devices and Radiological Health monitors radiological devices) issues its public warnings and advisories in the Radiological Health Bulletin. Before issuing a public warning or advisory, the FDA could negotiate with manufacturers in private (and in the case of Therac 25, with regulatory agencies in Canada). In response to reports of problems with a medical device, the FDA could, in increasing order of severity:

1. Ask for information from a manufacturer.
2. Require a report from the manufacturer.
3. Declare a product defective and require a corrective action plan (CAP).
4. Publicly recommend that routine use of the system on patients be discontinued.
5. Publicly recommend a recall.

In deciding on the response to a problem with a device, FDA needed to consider:

• Safety of the public.
• Safety of users of the device.
• Need for medical treatment with the device.
• Impact of the decision on the individual manufacturer.
• Impact of the decision on the medical device industry.