Doxylamine succinate is an antihistamine medication that blocks the effects of histamine, a chemical occurring naturally in the body 4. Doxylamine succinate is found in some over-the-counter sleep aids, such as Unisom and Wal-Som 4. 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 8. Doxylamine succinate is generally safe, but it can cause side effects that are usually minor but occasionally serious 4.
If you are experiencing serious medical symptoms, seek emergency treatment immediately.
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 4. 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 4.
Other Common Side Effects
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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 4.
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:
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.
- Serious side effects may occur with doxylamine, especially when a person takes more than the recommended dose.
- If this prevents the mucus from being coughed up, it may cause difficulty breathing or pneumonia, especially in people with chronic lung disease.
Warnings and Precautions
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Doxylamine succinate can interact with a large number of over-the-counter and prescription medications and supplements 4. 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 4. 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 4. Also talk with your doctor if you have a condition that could be worsened by fast or irregular heart beats, such as heart disease.
- Doxylamine succinate can interact with a large number of over-the-counter and prescription medications and supplements 4.
- 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 4.
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 14. 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 4.
All forms of doxylamine succinate should be avoided in women who are breastfeeding unless permitted by your doctor 4. 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 4. 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 4. 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.
- The doxylamine succinate-vitamin B6 combination medication Diclegis.
- All forms of doxylamine succinate should be avoided in women who are breastfeeding unless permitted by your doctor 4.
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- U.S. Food and Drug Administration: Example Drug Facts Label for Doxylamine Succinate 25 mg Tablet Dosage Form
- Drugs in Research and Development: Pharmacokinetic Dose Proportionality Between Two Strengths (12.5 mg and 25 mg) of Doxylamine Hydrogen Succinate Film-Coated Tablets in Fasting State -- A Single-Dose, Randomized, Two-Period Crossover Study in Healthy Volunteers
- BMJ Case Reports: Syndrome of Inappropriate Antidiuresis in Doxylamine Overdose
- DailyMed: Sleep Aid -- Doxylamine Succinate Tablet
- DailyMed: Diclegis -- Doxylamine Succinate and Pyridoxine Hydrochloride Tablet, Delayed Release
- Drugs.com: Doxylamine Pregnancy and Breastfeeding Warnings
- International Journal of Women's Health: Doxylamine Succinate–Pyridoxine Hydrochloride (Diclegis) for the Management of Nausea and Vomiting in Pregnancy -- An Overview
- Krystal AD, Richelson E, Roth T. Review of the histamine system and the clinical effects of Hi antagonists: basis for a noew model for understanding the effects of insomnia medications. Sleep Med Rev. 2013;17(4):263-272. doi:10.1016/j.smrv.2012.08.001
- Drugs and Lactation Database. Doxylamine. Bethesda, MD: National Library of Medicine (US). Updated December 3, 2018.
- MedlinePlus. Doxylamine. Updated February 18, 2020.
- "Doxylamine." Epocrates Rx Pro. Version 16.3, 2016. Epocrates, Inc. San Mateo, California.
Alicia Prater has been a full-time scientific editor and writer since 2008 and has contributed to many online publishers on a range of topics. Her preliminary dissertation work contributed to a peer-reviewed paper published in the "American Journal of Hypertension" in 2006. Prater received her Ph.D. in experimental pathology from New York Medical College.