Active ingredients and preparations of the H1 antihistamines


H1 antihistamine active ingredients and preparations of the first generation are presented below. In addition to the instructions for use listed below, please be sure to follow the instructions of your doctor or pharmacist as well as the package insert!

Also read: histamine


The active substance Clemastine (Trade name, etc. Tavegil®)) is available as a gel and tablet. Corresponding preparations are available over the counter in the pharmacy. The application can be used at itchy skin, allergic skin diseases, sunburn or insect bites. If necessary, the gel is applied thinly to the affected skin area. The antipruritic effect occurs quickly and lasts for up to 12 hours. Clemastine tablets can be used for severe allergic reactions and for chronic ones Urticaria be taken. They have a strong antipruritic effect. Clemastine in a first generation antihistamine and shows a sedating effect. It is therefore important to note that taking clemastine will impair your ability to drive!

Clemastine is not allowed with Antibiotics be taken. When additionally taking painkillers and psychotropic drugs as well alcohol the effect is increased and should therefore be avoided.

Dimentinden (Fenistil®)

The active ingredient Dimentinden (trade name including Fenistil®) is also available as a gel and tablet (see also: Fenistil® Gel). Corresponding preparations are available over the counter in the pharmacy. The gel can be used for short-term itching relief from insect bites, to relieve symptoms of sunburn and allergic skin symptoms.
The effect of Fenistil® lasts up to 4 hours. The gel is applied thinly to the affected skin area up to 3 times a day. The application must not be carried out over a large area or on sore, injured skin. In addition, the treated skin areas should not be exposed to direct sunlight. Occasional side effects, dryness and burning sensation are observed in the treated areas.
Dimentinden is also available in tablet form (Fenistil® tablets) for the treatment of more severe allergic skin symptoms, chronic urticaria and severe allergic rhinitis. It can also be given to children older than 3 years to relieve itching if they have chickenpox. Adults take 1-2 tablets 3 times a day, children> 3 years of age take 1 tablet 3 times a day.
As a side effect of Fenistil®, drowsiness and sleepiness are to be expected under certain circumstances, so that your ability to drive may be restricted! With simultaneous consumption of alcohol and sedating medication, the effect is increased.

You can find further information under our topic: Fenistil®


Preparations containing ketotifen require a prescription and impair the ability to drive and use machines.

Preparations with the active ingredient Ketotifen (Trade names including Ketofex®, Zaditen® ophtha sine eye drop) require a prescription! They can be used as tablets or eye drops for symptomatic relief, among other things. with allergic bronchitis, hay fever and allergic skin symptoms. The eye drops are more allergic to seasonal factors Conjunctivitis applied. The side effects of ketotifen include a headache, Tiredness, dizziness, Nausea and dry mouth are listed. Also Ketotifen Impairs the ability to drive and use machines.


Dimenhydrinate is also one of the first generation H1 antihistamines, but is primarily used to prevent or treat travel sickness, Nausea, vomiting and dizziness are used. It also has a sedating effect, which is usually desirable. It is i.a. in tablet form and as syrup in pharmacies freely available (trade names, etc. Vomex A®, travel tablets-ratiopharm). Dimenhydrinate preparations should be taken about half an hour to an hour before departure, whole with plenty of liquid. If necessary, a further intake is recommended after 4 hours during the journey. You should not exceed a maximum daily dose of 300 mg dimenhydrinate !! Dimenhydrinate and others must not be taken. at Cardiac arrhythmias, Difficulty breathing or. asthma, Liver dysfunction, glaucoma and epilepsy. As a side effect, dry mouth can accelerate Heartbeat (Tachycardia), Digestive problems and sun sensitivity occur. With the additional intake of alcohol, psychotropic drugs and painkillers, the effect is increased, which should therefore be avoided. Becomes Dimenhydrinate abruptly stopped after taking it over a long period of time sleep disorders occur.


Diphenhydramine (Trade names, etc. Betadorm®, Sediat®, Vivinox®) is a drug that can be sold over the counter in pharmacies for use in severe sleep disorders. Before going to bed one tablet (50 mg) I took plenty of fluids. Diphenhydramine should not be used for more than 2 weeks without medical consultation. Diphenhydramine should not be taken with liver dysfunction or bronchial asthma. During the treatment you should absolutely refrain from consuming alcohol, as this will unpredictably impair the effect of diphenhydramine. In addition, the ingestion affects the ability to drive, also when using machines. Pregnant women and breastfeeding women must not use diphenhydramine!


Promethazine (Trade name Atosil®) is a prescription sedative for adults and is available as tablets and drops. It is used for restlessness and agitation in connection with underlying psychiatric illnesses and as an alternative for nausea, vomiting and sleep disorders, if other drugs were not effective. The dosage depends on the type of complaints to be treated and the underlying disease. Since sedative effects are to be expected on the following day, it should be taken into account that the ability to drive and operate machines is impaired. Simultaneous use of other drugs from the group of Antihistamines (Medicines against nausea), painkillers, sedatives, psychotropic drugs and alcohol lead to a reciprocal effect and should therefore be avoided!

2nd generation H1 antihistamines:

The active ingredients of H1 antihistamines of the second generation are primarily anti-allergic. They lack a calming, sleep-promoting effect. In addition, they have a faster onset of action and a longer duration of action compared to the first generation.

The active ingredients and preparations are presented in more detail below. In addition to the recommendations for use from a doctor or pharmacist, the package insert should also be taken into account!


The active substance Cetirizine is an over-the-counter antiallergic drug available in pharmacies. It is available in tablet form and as drops. Cetirizine tablets are swallowed whole with plenty of water once a day. In the case of severe symptoms, it can also be taken in the morning and in the evening. When dosed properly, this active ingredient shows no interaction and hardly any side effects. In the absence of sufficient data on pregnancy and lactation, it should not be used in these circumstances. Cetirizine must also not be taken in epilepsy.

Available preparations: i.a. Zyrtec®, Reactine®, Cetirizin ratiopharm®


Loratadine is also an over-the-counter antiallergic for the treatment of hay fever and chronic urticaria. It is available as a tablet and an effervescent tablet with 10 mg of active ingredient. It should be taken once a day in the morning with meals. If the symptoms are severe, an additional tablet can be taken before going to bed.

Available preparations: i.a. Lisino S®, Lisino® effervescent tablets, Loratadine-ratiopharm®


Azelastine is primarily used to treat hay fever and related complaints such as Itchy eyes, conjunctivitis, runny or blocked nose are recommended. It can be used all year round. Azelastine preparations are available over the counter in pharmacies as tablets, eye drops and Nasal sprays. One tablet can be taken up to twice a day. One drop of the eye drops is put into the eye two to four times a day. One puff of the nasal spray should be used twice a day. Occasional side effects such as fatigue or local irritation when applied to the eye are to be expected during treatment with azelastine. Azelastine-containing products must not be used together with cetirizine-containing products, since interactions are to be feared !!

Available preparations: i.a. Allergodil® eye drops / nasal spray / tablets, Vividrin® Eye drops / nasal spray

General advice on the use of antihistamines

  • It can be taken in tablet form regardless of meals.
  • The duration of use is not limited and can be done as required.
  • Please note that no allergy test (skin test) should be carried out during therapy with an antihistamine. The income could hide or weaken a positive result!
  • Antihistamines should not be used if a cold is not of allergic origin.
  • While pregnancy and breastfeeding, antihistamines should, if possible, not be used without medical advice! For many preparations there are not yet sufficient data for the use during pregnancy and breastfeeding. Active ingredients such as dimenhydrinate are not suitable for the long-term treatment of nausea / vomiting during pregnancy.

Risk of overdose

If antihistamines are taken in amounts above the therapeutically recommended dosage, poisoning can occur. Symptoms of poisoning appear in different degrees, among other things. noticeable through tiredness and fatigue, a headache, Ringing in the ears, red, swollen face, constipation or diarrhea, Dry mouth, fluctuations in blood pressure, muscle tremors and twitching, dilation of the pupils with sluggish pupillary reactions, blurred vision, greatly increased body temperature. Extremely high doses lead to coma, cardiac and circulatory failure. In the event of poisoning, a doctor must be consulted immediately, who can take appropriate countermeasures!

H2 antihistamines

H2 antihistamines have a different field of application than H1 antihistamines. They lower the production of Stomach acid in the Gastric mucosa and are therefore used in the treatment of gastric acid-related complaints, such as used in the stomach or duodenal ulcer. With the H2 antihistamines, hardly any undesirable effects on other receptor types are to be expected.

Active ingredients and trade names:

Cimetidine (i.a. Cimetidine-CT), ranitidine (including Ranidura® T), famotidine (including Pepdul®, Famonerton®)


Gastrin is an endogenous messenger substance that occurs primarily in the gastric mucosa. After gastrin attaches itself to the cell surface of the ECL cells located in the gastric mucosa, they release histamine. The released histamine binds to associated receptors (H2 receptors) on the surface of neighboring cells of the stomach lining, the so-called parietal cells. As a result, the parietal cells produce more stomach acid and release it into the interior of the stomach. H2 antihistamines compete with histamine for the H2 receptors on the cell surfaces. If the H2 antihistamine binds, the histamine-typical effect does not occur and the release of acid into the stomach is reduced. Lowering gastric acid production is the goal of therapy for acid-related stomach problems such as stomach or small intestinal ulcers. They can also be given as a preventative measure if the ulcer has healed to prevent it from coming back. However, they must not be used for nervous stomach problems such as heartburn! This should be on Antacids can be used. H2 antihistamines require a prescription and cannot be obtained from pharmacies without a prescription. Serious stomach problems require a detailed medical examination! H2 antihistamines are administered in tablet form. Depending on the doctor's prescription, they are taken once or twice a day - in the morning with meals and, if necessary, in the evening before going to bed. The onset of action usually takes place within 1-2 hours. The ulcer pain usually disappears within a few days. However, treatment should last at least 4 weeks for the ulcer to heal.

When taking it, it should be noted that H2 antihistamines must not be taken together with anticoagulants such as warfarin, beta blockers (drugs against high blood pressure) or antacids. H2 antihistamines strengthen the effect of alcohol, which is why taking them at the same time should be avoided. Occasionally, diarrhea, headache, dizziness, itching, and skin rashes have been observed as side effects of ingestion. Famotidine may cause dry mouth, nausea and vomiting.

Exclusion of liability / disclaimer

We would like to point out that medication must never be discontinued, applied or changed independently without consulting your doctor.
Please note that we cannot claim that our texts are complete or correct. The information may be out of date due to current developments.