It depends what dosage of Darvocet you're referring to.

Lortab 7.5 has 500 mg of acetaminophin and 7.5 mg of hydrocodone.

Darvocet A 500 has 500 mg of acetaminophin and 100 mg of propoxyphene napsylate.

Darvocet N 100 has 650 mg of acetaminophin and 100 mg of propoxyphene napsylate.

Darvocet N 50 has 325 mg of acetaminophin and 50 mg of propoxyphene napsylate.

In both medications the purpose of the acetaminophin is to boost the effectiveness of the opioid. 

I understand your fear of addiction and your concerns in light of what happened to your sister.  It's important to understand the difference between addiction and physical dependence. 

People who take opioid medications like Lortab or Darvocet on a regular basis for chronic pain will usually become physically dependent on them.  That simply means if you were to discontinue the medication suddenly, you would experience physical symptoms of withdrawal.  Chronic pain patients don't usually experience a "high" from opioid medications – merely a relief from pain. 

Addiction, on the other hand, happens when people take an opioid drug to achieve a "high."  It takes ever-increasing amounts of the drug to produce the high and they become focused on getting more and more of the drug. 

I would encourage you to talk to both your doctor and your pharmacist about your concerns.  They should be able to explain the difference between the two medications and to answer any questions you might have about addiction and possible problems from the acetaminophin.

Karen