The latest developments in the death of reality TV star Anna Nicole Smith's son once again gives us the opportunity to use a tragic news story to highlight a very important health issue.

According to a recently released autopsey report, Smith's son, Daniel, died of an apparent heart attack brought on by a lethal combination of at least three different drugs. One of those drugs, methadone, was allegedly given to Daniel by Smith's companion, Howard K. Stern.

There are several reasons why you should never share a prescription with someone-- even if you think it will help the person. Giving someone a portion of a prescription that was written for you can have serious unforeseen consequences.

Every individual responds to a drug in a different way. Your body’s response is determined by factors like your genetics, your age, your body size, any medical conditions you may have and whether or not you've also taken other drugs or dietary supplements.

The first problem with sharing a prescription that was meant for you is that the person you give it to may be allergic to the drug. An allergic reaction means that the patient's immune system overreacted to the drug when it was taken and produced an antibody called immunoglobulin E in response to the drug. If the body is given the drug again, the allergy antibody, which bound itself to specific cells called mast cells, will release histamine and other chemicals. This produces symptoms of an allergic reaction, which can be mild in form like hives, or severe like anaphylaxis.

Anaphylaxis is an extremely lethal form of allergic reaction. Its symptoms include a feeling of warmth, becoming flush, itching, swelling in the throat, asthma or wheezing, light-headedness, irregular heartbeat, nausea or vomiting, abdominal cramping, and shock. If the person experiencing anaphylaxis isn’t given immediate medical attention, he or she could die.

Because there are so many factors that affect a person’s response to a drug, when doctors prescribe medication they are careful to adjust the dose to fit the individual patient. Drugs are typically measured in milligrams. There are 453,592.37 milligrams to a pound. Doctors use this micro measurement because the tiniest amounts of these substances are very powerful and the dosage amount must be precisely correct for the individual taking it to produce the desired results. Since no two individuals have exactly the same body type, weight, and genetic composition, a prescription that is well suited to one individual can never be right for another.

Another reason you should never share a prescription is that by not taking the complete prescription as directed yourself--the required course of treatment-- you won’t recover the way you should. If you don’t fully recover, you remain highly susceptible to a relapse.

Finally, in addition to not sharing medications, you should never stockpile them either. If you try to save time and money by keeping unused portions of prescriptions to take should you become sick again, you’re playing doctor and making your own diagnosis. Since you don’t have the medical training to do this, you may not only be wrong in your diagnosis, but you may also do some serious harm to your health.

Additionally, drugs do not have long shelf lives and change chemical composition over time. Taking an old prescription that may have become chemically altered can also do significant injury to your health.

If someone you know needs a prescription to treat a medical condition, they need to see their doctor. Only a trained medical professional knows how to formulate the right prescription that can treat the condition and fit the individual’s body chemistry.

Foxnews.com Health contributor Maria Esposito contributed to this report.

Click here to check out Dr. Manny's book The Check List (Harper Collins, 2007)

Dr. Manny Alvarez is the managing editor of health news at FOXNews.com, and is a regular medical contributor on the FOX News Channel. He is chairman of the Department of Obstetrics and Gynecology and Reproductive Science at Hackensack University Medical Center in New Jersey. Additionally, Alvarez is Adjunct Professor of Obstetrics and Gynecology at New York University School of Medicine in New York City.

Dr. Manny Alvarez serves as Fox News Channel's senior managing health editor. He also serves as chairman of the department of obstetrics/gynecology and reproductive science at Hackensack University Medical Center in New Jersey. Click here for more information on Dr. Manny's work with Hackensack University Medical Center. Visit AskDrManny.com for more.