Doxylamine succinate is an antihistamine medication that blocks the effects of histamine, a chemical occurring naturally in the body. Doxylamine succinate is found in some over-the-counter sleep aids, such as Unisom and Wal-Som. It is also combined with decongestants and other medicines in a number of over-the-counter cold or allergy medicines, such as NyQuil and Tylenol Sinus. When combined with vitamin B6 in the prescription medication called Diclegis, doxylamine is used to treat nausea and vomiting during pregnancy. Doxylamine succinate is generally safe, but it can cause side effects that are usually minor but occasionally serious.
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Doxylamine succinate often causes drowsiness, which is considered a beneficial effect when used as a sleep aid but a side effect when used for other purposes. Drowsiness tends to be more common and more severe in older adults. This increases their risk of falling when taking doxylamine. Consuming other medicines with sedating effects -- such as antidepressants, muscle relaxants or opioid painkillers -- and drinking alcohol also increase the likelihood of drowsiness. Sometimes doxylamine succinate causes the opposite of drowsiness, producing nervousness, irritability or insomnia.
Other Common Side Effects
There are a number of other possible side effects of doxylamine succinate, including headaches, dizziness, blurred vision, dry mouth and nose, ringing in the ears, constipation and difficulty urinating. The dizziness is often caused by a fall in blood pressure when a person stands up. Difficulty with urination is more common in people with preexisting urination problems, such as men with an enlarged prostate. A small increase in heart rate is a common side effect of doxylamine succinate.
Serious Side Effects
Serious side effects may occur with doxylamine, especially when a person takes more than the recommended dose. These may include nervous system effects, such as confusion, disorientation, tremors, seizures and coma. Worsening of glaucoma -- a condition caused by increased pressure within the eye -- may also occur. Very fast or irregular heart beats are other possible serious effects. Sometimes the drying effects of doxylamine cause mucus within the lung to become unusually thick. If this prevents the mucus from being coughed up, it may cause difficulty breathing or pneumonia, especially in people with chronic lung disease.
According to an article reported in the May 2011 issue of “Erciyes Medical Journal,” inflammation of the pancreas -- called pancreatitis -- or breakdown of muscles -- known as rhabdomyolysis -- are possible, though rare, side effects of too much doxylamine succinate. These are potentially life-threatening conditions. A report published in "BMJ Case Reports" in November 2012 described a woman who developed syndrome of inappropriate antidiuresis (SIAD) from a doxylamine overdose. This syndrome causes low blood levels of sodium, which may lead to seizures or even death.
Warnings and Precautions
Doxylamine succinate can interact with a large number of over-the-counter and prescription medications and supplements. In many cases, combining doxylamine with these substances increases doxylamine side effects. Before taking doxylamine, discuss all medications and supplements with your doctor to avoid interactions. When taking any medication containing doxylamine succinate, avoid driving or operating heavy machinery if you develop drowsiness. Avoid consuming alcohol while taking doxylamine.
Doxylamine succinate should be taken only under a doctor’s instructions if you have certain medical disorders, such as chronic lung disease, glaucoma, an enlarged prostate or other causes of difficult urinating. Also talk with your doctor if you have a condition that could be worsened by fast or irregular heart beats, such as heart disease.
Use in Pregnancy, Breastfeeding and Children
The doxylamine succinate-vitamin B6 combination medication Diclegis is approved by the U.S. Food and Drug Administration (FDA) for treating nausea and vomiting in pregnant women. Doxylamine succinate in other forms during pregnancy is probably safe for you and your baby, but you should ask your doctor before taking any medication if you are pregnant.
All forms of doxylamine succinate should be avoided in women who are breastfeeding unless permitted by your doctor. Doxylamine can be passed through breast milk and cause sedation or irritability in breastfed babies. It may also reduce milk production.
The safety of doxylamine succinate in young children has not been established. Children may be more sensitive to the effects of doxylamine than adults. Furthermore, children are more likely than adults to develop agitation with any antihistamine. The FDA recommends that doxylamine succinate not be used to treat insomnia in children younger than 12 years old. For cold or allergy symptoms, doxylamine should not be used in children younger than 2 years of age. In children older than 2, check with your doctor before use.
Reviewed by: Mary D. Daley, M.D.