Propoxyphene is an opioid given the brand name Darvon or Darvon-N. Introduced in 1957, it is a synthetic narcotic frequently prescribed for mild to moderate pain. Most commonly it is prescribed in the form propoxyphene napsylate and this information is completely useless to most people.
Let's start over. If you find yourself at a doctor or dentist's office complaining of pain that aspirin doesn't help, they are likely to first prescribe darvocet, a very mild painkiller. Darvocet's narcotic element is propoxyphene; they take usually 100 mg of proproxyphene (which is a synthetic opiate) and they put it with about 700 mg of acetaminophen. Such a dosage (most likely found in pill form) is good for about 3-4 hours or pain relief.
Propoxyphene can cause nausea, vomiting, and lightheadedness so you don't want to take it on an empty stomach. Unfortunately, it won't work very well for long. The problem with propoxyphene is that, while it is mildly ineffective, it is most definitely habit-forming. Structurally similar to methadone, overdosing on propoxyphene is easy and dangerous.
You should be careful not to take more than the prescribed dosage. Because propoxyphene won't provide immediate relief, many people are tempted to double-up on their own. This will cause your breathing to go shallow, your heart rate to change and will probably make your skin very itchy. Worse still is coming up with creative ways to combine medicines. Taking propoxyphene with other drugs (including alcohol) can be very dangerous. Rather than running the risk of overdose, consult with your physician. S/he would much rather try something different than see you take matters into your own hands.
Information courtesy of the saga.