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Side Effects of Dihydrocodeine (Synalgos-DC, Trezix, Zerlor, Panlor)


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Side Effects of Dihydrocodeine (Synalgos-DC)

Dihydrocodeine, available under the brands Synalgos-DC, Trezix, Zerlor, and Panlor, is a narcotic analgesic medication used to relieve moderate to severe pain.

Warnings before Synalgos-DC Treatment

The FDA gives warnings before taking Synalgos-DC.


Long-term regular use of Synalgos-DC can lead to addiction, which might cause restlessness and irritability when it is stopped.


Avoid the medication if you have liver disease, breathing problems; such as obstructive airways disease or respiratory depression. A condition where the small bowel (part of your gut) does not work properly (paralytic ileus), an asthma attack, alcohol addiction; feel sick due to a head injury or increased pressure in your skull (for instance due to brain disease), a severe headache, or an intolerance to some sugars.

Serious Side Effects

Synalgos-DC intake should be stopped immediately in case of swelling of the hands, feet, ankles, face, lips or throat (which may cause difficulty in swallowing or breathing), itchiness, hives (skin reaction) which might indicate an allergic reaction to Synalgos-DC, and slower and weaker breathing (this could be a serious side effect known as respiratory depression).


Severe stomach pain that reaches out to the back could be a sign of inflammation of the pancreas (pancreatitis). This is a very rare but serious side effect, affecting less than 1 in 10,000 people.

Common Side Effects

Common side effects associated with Synalgos-DC are:


  • Constipation (Laxatives may be prescribed)
  • Feeling or being sick (Normally wears off after a few days)
  • Drowsiness (more likely to occur in the beginning of treatment or when dose is increased and should wear off after a few days)
  • Dry mouth
  • Abdominal pain
  • Discomfort

(Synalgos-DC label as reported by the FDA).

Drug Interactions

Certain medications may interact or interfere with Synalgos-DC, such as medicines used to treat depression. These are called MAOIs (monoamine oxidase inhibitors): moclobemide, phenelzine, tranylcypromine, CNS (central nervous system) depressants, medicines which make you drowsy or sleepy, metoclopramide (a medication used to stop nausea or vomiting), and prescriptions used to treat psychiatric conditions or mental disorders (phenothiazines).

About Pharmacogenetic Testing

Psychiatric conditions affect 1 out of 4 people. Genetic testing aims to help people by testing their DNA and seeing how those genes interact with the medications. It saves people money, time and helps avoid adverse reactions. All that is required is a swap to collect sample cells from inside the surface of the cheek.

Know Your Risk with the Rxight® Genetic Test

MD Labs provides the CLIA-certified Rxight®, which analyzes how your body will react to hundreds of types of prescription and over-the-counter (OTC) medications. When you are aware of how you personally metabolize drugs, you and your doctor can make more fully informed medical decisions and avoid adverse reactions.


To get more information on the Rxight® genetic test, call us at 1-888-888-1932 or email us at support@Rxight.com.


Contributors to this Article:
Michael Sapko, MD, PhD; and Deborah Kallick, PhD, Medicinal Chemistry