Long-Term Effects of Nyquil

Nyquil is a type of over-the-counter medicine that contains a combination of ingredients. It is designated to treat symptoms caused by bronchitis, sinusitis, allergies, flu and the cold virus. Nyquil contains dextromethorphan, acetaminophen, oral antihistamines and decongestants 1. While Nyquil is safe when used as directed for short-term use, prolonged use over time can pose a serious health risk. Some of the ingredients in Nyquil can have long-term effects on the body 2.


One of the most serious long-term effects of Nyquil is addiction to the product 2. Most people only use the drug temporarily or as needed to help fight their allergy, cold and flu symptoms. Nyquil is generally a safe product when taken as directed. There are some people who abuse the medication in order to achieve the high from taking excessive amounts of dextromethorphan 1.

Dextromethorphan works at suppressing the receptors in the brain that control coughing 1. When the pills are crushed or the gel is broken on a tablet, the ingredients are released at once rather than gradually released. According to CESAR or Center for Substance Abuse Research, when taken in high amounts above the recommended dosage on the package, Nyquil has been reported to create dissociative, psychedelic and euphoric effects on the body 2. It can become addictive because of this, therefore some people seek the medicine to get high rather than treat their cold or respiratory illness.

Disease Complications

Another possible long-term effect from taking Nyquil could be the affect it has on an underlying disease. One of the ingredients in some of the Nyquil products contains high fructose corn syrup, a type of sugar. The four Nyquil liquid medicines including Cold and Flu, Cough, D and Less Drowsy all contain the sweetener. The Vicks.com website suggests anyone who has diabetes should consult with their physician before taking Nyquil products. Excessive sugar intake may increase blood sugar levels and fluctuate the amount of insulin or diabetic medication needed to bring glucose levels to a normal level. People with intestinal blockages, constipation or bowel problems, can experience worsened symptoms and Nyquil can interfere with treatment. It may also affect people who have hyperthyroidism, an enlarged prostate or urinary retention.

Liver Damage

Someone suffering from any type of liver disease or liver-related problem should use extreme caution when taking Nyquil. The product contains acetaminophen. This is a non-aspirin medication that is used to treat pain and reduce fever. According to the Center for Substance Abuse Research, even in healthy patients with no liver problems, if they take high amounts of acetaminophen, a long-term effect may result in liver damage.


The Nyquil website suggests that all pregnant and breast feeding women seek advice from their physician before taking any of their products. Women who take any of the Nyquil cough syrups while pregnant pose a serious long-term health risk to their unborn baby. The reason for this is they all contain alcohol as an ingredient. The antihistamines in Nyquil can lead to seizures and breathing problems in-utero. Even after the baby is born, it can leak into breastmilk if the mom is taking the medication for an illness or abusing the drug. The same side effects she feels from the medication can also be passed on to the infant 2.

Vital Sign Changes

According to the Center for Substance Abuse Research, Nyquil can have a long-term effect on vital signs for up to six hours after the product is taken. It can increase blood pressure and heart rate. In some cases it can cause tachycardia or an excessive heart rate over 120 beats per minute. As a result of increased heart rate and blood pressure, users may also experience a panic attack.

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