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How Long Does Dextromethorphan Take to Be Effective?

author image Adam Cloe Ph.D./M.D.
Adam Cloe has been published in various scientific journals, including the "Journal of Biochemistry." He is currently a pathology resident at the University of Chicago. Cloe holds a Bachelor of Arts in biochemistry from Boston University, a M.D. from the University of Chicago and a Ph.D. in pathology from the University of Chicago.
How Long Does Dextromethorphan Take to Be Effective?
Dextromethorphan may ease your symptoms. Photo Credit: IPGGutenbergUKLtd/iStock/Getty Images

Dextromethorphan Forms and Effects

Dextromethorphan is a medication that is used to relieve coughing problems because of colds or influenza (see link in References). Dextromethorphan is not indicated for the treatment of coughs caused by asthma, smoking or emphysema. It works by suppressing the cough reflex by acting directly on the part of the nervous system that controls coughing. Dextromethorphan can be obtained in the form of lozenges, syrup and a suspension (a mixture of the medication in which it is not completely dissolved) which allows for more gradual and extended release of the drug.


Dextromethorphan begins to take effect as soon as it enters the blood stream, which is soon after it is absorbed by the digestive system, which generally occurs within 15 minutes after ingestion. Its adsorption and metabolism rates are listed on for oral ingestion of the standard dextromethorphan syrup. It reaches its maximum level within the blood approximately 2 1/2 hours after ingestion. One of its metabolites (which means a compound that is made after dextomethorphan is broken down by the body), dextrorphan, reaches its peak levels approximately 2 hours after the medication is taken. Dextrorphan also has anti-cough effects.


Oddly enough, dextromethorphan's window of being effective varies from person to person due to differences in the way that people metabolize and break down dextromethorphan. The liver breaks down dextromethorphan initially by using the cytochrome P-450 protein. Because of genetic variations, some people have a faster working cytochrome P-450 system than others. For people with fast dextromethorphan metabolism, a standard dose (30 mg) will be almost undetectable in the blood after 5 hours. People with intermediate metabolism will have levels of dextromethorphan significantly drop after 4 hours and be clear of the system after 24 hours. Slow metabolizers of dextromethorphan will still have the medication in relatively high amounts in the bloodstream after 4 hours and the dextromethorphan can still be readily detected in the blood after 24 hours.

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