When a new medicine is first developed and approved for use, it is usually only available from one manufacturer. Normally, that is the company that invented it and that obtained the first authorisation for its use, after steering the drug through the complex and expensive process of clinical trials.
New drugs are normally very expensive (see our resource Why are some medicines so much more expensive than others?). This is because they are protected by patents and/or the regulatory authorities give the original manufacturer a period of market exclusivity as an incentive to develop drugs for rare diseases (eg so-called Orphan Drug Designation). All of this means that the original manufacturer has a monopoly on supply of the drug. In other words, there is no competition in the marketplace and the manufacturer can charge a very high price. One example of a drug to which this still applies is sodium oxybate, which is currently only produced by Jazz Pharmaceuticals and is only available under their trade name, Xyrem®.
Eventually, however, patents and other forms of protection expire, and it then becomes possible for other companies to produce competing copies of the original product, provided that they show to the regulatory authorities that their product is effectively the same as the original. The competing companies still cannot use the original company's trade name, but they simply refer to the drug by its “generic” name. An example of a drug that has reached this situation is modafinil. The original product – produced by Cephalon, which is now part of TEVA – was (and still is) marketed under the trade name PROVIGIL. Now, however, a number of other companies produce competing versions of modafinil. Those products should be equivalent to the original.
Generally speaking, as soon as a drug becomes “generic” and alternative products become available, the resulting competition in the marketplace drives the price down, sometimes dramatically. Medicines that were previously very expensive become much more affordable, physicians are not so reluctant to prescribe them on cost grounds, and they therefore become more accessible to patients.
Patients who previously received the original, branded medicine may therefore find that they are subsequently given a generic equivalent. This should be identical to the original product in its therapeutic effect. However, we have received some reports of people with narcolepy feeling that generic medicines are not as effective as the branded product that they have previously taken. It is not out of the question that there could be differences (perhaps as a result of different companies using slightly different manufacturing processes, or using slightly different additional ingredients in their products). If you feel that a generic medication is not as effective as the branded equivalent, you should discuss the matter with your doctor.
Another issue that can occur is that sometimes there can be a shortfall in the supply of a medication produced by a particular company. Where the drug is generic, there is usually at least one alternative supplier. In the UK, for instance, there are at least two suppliers of generic modafinil, in addition to PROVIGIL. Similarly, there are several suppliers of dexamfetamine and of methylphenidate. If your doctor tells you that your usual medication is temporarily unavailable, you should ask whether there is an equivalent drug available from another source.