Guide on Antihistamines – Types, Side effects, Precautions and More

People can get different types of allergies ranging from sneezing to runny nose and more. So to treat such conditions, antihistamines are used. But the interesting thing is that these drugs can actually cause the user to fall asleep, making them very useful for treating insomnia.

So this guide is all about that, we will talk about antihistamines and sleep and will discuss the types of antihistamines, side effects, precautions and more in this guide so make sure to stick to the end.

What Are Antihistamines?

An antihistamine is a medicine type that is used for the treatment of common allergy symptoms like hives, sneezing, watery eyes, and runny nose etc. There are some antihistamines that are used for the treatments for nausea, motion sickness, sleep problems, cough, Parkinson’s disease and anxiety.

These drugs block the effects of histamine which is a substance in the body that causes the symptoms of allergy. There are different forms of antihistamine including tablets, capsules, injections, liquids and eye drops and can be purchased OTC (over the counter) or given as a prescription by a doctor.

How Do Antihistamines Work?

Antihistamines work by blocking central histamine in your body which are actually the (H-1) histamine-1 receptors in your brain. So when this happens, the user starts to fall asleep and get a good night’s sleep because H-1 targeting antihistamines are the strongest when it comes to making user fall asleep.

The antihistamines that you usually see in the over-the-counter sleep aids are usually hydroxyzine and diphenhydramine. These type of antihistamines affect H-2, H-3, and H-4 receptors which provide mild sleep and not as strong as the H-1 receptors. So as a result, people quickly build a tolerance to these H-2, H-3, and H-4 receptors over time and when they stop taking these medicines, they experience the rebound insomnia.

Antihistamines are also called the histamine agonists and are administered to fight different allergic reactions, which means people may not want to get sleep, and it might be considered as an undesirable effect. However, people who need to get some sleep, they can benefit from the drowsiness that comes with the use of antihistamines. These type of drugs are usually not prescribed, rather purchased from retailers over the counter.

Keep in mind that these drugs have potential side effects if you take them with other drugs, so if you are taking them with other types of drugs, you should always inform your doctor about that.

Use of Antihistamines for Insomnia:

Antihistamines are usually the first sleep medication for insomniacs and they are usually sufficient. You don’t need any prescription from the doctor to use them because the regulatory authorities have decided that they are safe enough to be used by responsible adults unsupervised.

Just like all types of sleep medications, antihistamines also artificially modify the sleep patterns of a person and sometimes leave the user groggy the very next day and the quality of sleep sometimes can be less than natural. However, according to some users, the tradeoff to stop insomnia and get at least some sleep is totally worth it. There is also a possibility involving drug resistance where the body can adapt to antihistamine and does not work as well.

Also, like other types of hypnotics, the effectiveness of antihistamines, in the long run, has not been demonstrated in a way that can satisfy the scientists. But that doesn’t mean that these drugs don’t work at all, it simply means that the official science is still skeptical on this matter.

Doctors usually and frequently recommend the use of antihistamines over the common prescription sleep medicines when the patient has insomnia because of the withdrawal from drug and alcohol. This strategy is expected to reduce cross dependence risk. So make sure to run this idea by your doctor as mixing sleeping pills and other type of substances can have a serious health risks.

Lastly, the brain signals that need to keep the user awake include the histaminergic signals. So the antihistamines that target H-1 receptors block those signals as well and that makes us sleepy. Some antihistamines can even get across the blood-brain barrier and reach the relevant receptors. These drugs include diphenhydramines that are very useful sedatives.

Types of Antihistamines:

  • Doxylamine: This type of antihistamines can itself be used as a sleep aid or it can also be combined with other medicines for allergy and cold relief. It is sometimes also used with Vitamin B6 during pregnancy to stop the morning sickness. Keep in mind that Doxylamine is one of the most powerful over the counter sedatives found in the U.S. and it can even be more powerful than some hypnotic drugs. Many patients using Doxylamine encounter side effects such as nausea, dry mouth and drowsiness.
  • Diphenhydramine: This is the first antihistamine that was approved by the Food and Drug Administration (FDA) in the 1940s and now it is widely used in many over the counter sleeping pills. There are many generic sleep medicines that solely contain only one active ingredient and that is diphenhydramine. It is one of the oldest antihistamines that are available now and is also classified as the first-generation antihistamine. Though it is so old, it surpasses some of the new prescription drugs for many patients. Many doctors use the diphenhydramine when significant histamine is released and needs a fast and very effective reversal such as in conditions like motion sickness, allergic rhinitis, hives, stings and insect bites. Some of its common side effects include profound drowsiness, urinary retention, difficulty concentrating and dizziness.
  • Hydroxyzine: This one is also used for allergies and to treat nausea. Keep in mind that the use of hydroxyzine only for the sake of getting sleep is not appropriate.
  • Triprolidine: This antihistamine is mostly used in Europe and the interesting thing is that its half-life is shorter than some antihistamines.
  • Niaprazine: Another type of antihistamines that was invented in France and this one is also mostly used in the European Union. The primary reason why niaprazine is used is for its intense sedative effects and its use can result in conditions like day time sedation and vertigo.
  • Pyribenazamine: This is also a first-generation antihistamine and is less frequently used in today’s world as many new antihistamines have hit the market. This one is typically used for the treatment of asthma, hay fever, rhinitis and urticaria and is also a mild sedative. Some common side effects of pyribenzamine are gastrointestinal irritation, nausea, dry mouth and dizziness.
  • Clemastine: It is used for treating symptoms of allergy including pruritus and rhinitis. Though it is also a sedative antihistamine, its effects are not much intense than many other medicines of this nature. The side effects of this drug greatly depend on what its dose is and can sometimes also produce contradictory responses. However, some of the most common side effects include, blurred vision, dry mouth, drowsiness and dizziness.

Side Effects of Antihistamines:

There are some side effects that can occur with the use of antihistamines and some of the most common ones include:

  • Sleepiness or drowsiness
  • Dry nose, throat or mouth
  • Dizziness
  • Mucus getting thick
  • Vision changes
  • Weight gain and increased appetite
  • Feeling irritable, excited or nervous
  • Upset stomach

If any of these side effects occur, it is imperative that you inform your doctor.

Precautions Before Taking Antihistamines:

Before you start using antihistamines, it is crucial that your doctor knows about all medical conditions that you have and make sure to especially tell them about the ones given below:

  • Hyperthyroidism
  • Glaucoma
  • Heart disease
  • Epilepsy
  • High blood pressure
  • Enlarged prostate
  • Trouble urinating
  • Diabetes

Also, just to be on the safe side, tell your doctor if you are pregnant so that they can take this condition into consideration when prescribing any antihistamines.

Tips for Taking Antihistamines:

  • The first and the most important thing that you should keep in mind is that you should never combine antihistamines with other sleeping medicines or with alcohol.
  • You should not drive, operate machinery or perform activities that require you to be alert after you have taken antihistamines.
  • Follow all instructions provided on the package label or your prescription carefully when you take an antihistamine and don’t take any more medicine than the recommended dose.
  • Inform your doctor if you are taking, have taken or plan to take any prescribed, non-prescribed, recreational, illegal, herbal, dietary or nutritional drugs before you start using antihistamines.
  • You may need to avoid eating grapefruit or drinking grapefruit juice while taking antihistamines because they can affect how antihistamines work in your body. Talk to your doctor about it if it is a problem for you.

Over to You:

Well, that is all about the basics of antihistamines, types, side effects, and precautions. Now that you know how dangerous these drugs can be if combined with other sleep medicines or alcohol, you should always avoid doing so.

Furthermore, make sure to discuss all the health conditions you have or had in the past with your doctor before using antihistamines and also tell her/him if you are going to take any drugs with antihistamines to be completely safe.