Over-the-counter (OTC) medicines are medicines you can buy without a prescription from your doctor. Antihistamines help relieve or prevent allergy symptoms. Two types of OTC antihistamines are available: first-generation and second-generation antihistamines. Both types can be useful for allergies. First-generation antihistamines are also sometimes used in OTC cold medicines.
When your body is exposed to allergens, it releases histamines. Histamines attach to the cells in your body and cause them to swell and leak fluid. This can cause itching, sneezing, runny nose, and watery eyes. Antihistamines prevent histamines from attaching to your cells and causing symptoms.
First-generation antihistamines also work in the part of the brain that controls nausea and vomiting. This is why they can help prevent motion sickness. Because 1 of the most common side effects of first-generation antihistamines is feeling sleepy, they are sometimes used to help people who have trouble sleeping (insomnia).
Note: Both types of antihistamines often are mixed with other medicines, such as pain relievers or decongestants. Many of the brand names above are for these combination medicines, which are meant to treat many symptoms at the same time. In general, it’s a good idea to treat just the symptoms that you have. For example, if you have only a runny nose, don’t choose a medicine that also treats headache and fever.
Read the directions on the drug facts label to learn how much medicine to take and how often to take it. If you have any questions about how much medicine to take, call your family doctor or pharmacist. Keep a record (1-page PDF; About PDFs) of the OTC medicines you are using and when you take them. If you need to go to the doctor, take this list with you.
Follow these tips to make sure you are taking the right amount of medicine:
Store all medicines up and away, out of reach and sight of young children. Keeping medicines in a cool, dry place will help prevent them from becoming less effective before their expiration dates. Do not store medicines in bathrooms or bathroom cabinets, which are often hot and humid.
Healthy adults don’t usually experience side effects from antihistamines. However, side effects can be a concern for older adults or people who have health problems.
First-generation antihistamines may make you feel sleepy. This can affect your ability to drive or operate machines, and it may be hard for you to think clearly. Alcohol can increase the drowsiness caused by antihistamines. Antihistamines may cause your mouth and eyes to feel dry. They can also cause abdominal pain and headaches. Second-generation antihistamines are less likely to cause these side effects.
Antihistamines can interact with other medicines you take. If you take any of the following medicines, talk to your doctor before taking a first-generation antihistamine:
Antihistamines are often combined with decongestants and/or pain relievers. If you take 1 of these combination medicines, it’s important to understand each of the active ingredients and the interactions they may have with other medicines you’re taking.
Be sure not to take too much antihistamine. Many OTC cold and allergy medicines contain antihistamines, and some prescription medicines do, too. If you take more than 1 of these medicines, you may get much more antihistamine than you intend.
Second-generation antihistamines are less likely to interact with other medicines you are taking.
Talk to your doctor before using a first-generation antihistamine if you have any of the following health problems:
If you have kidney or liver disease, talk to your doctor before taking a second-generation antihistamine.
Funding and support for this material have been provided by the Consumer Healthcare Products Association.
Written by familydoctor.org editorial staff