Side effects of antihistamines

Like all medicines, antihistamines can have side effects. Generally, these are moresignificant with first-generation antihistamines. For a full list of specific side effectsof your medicine, see the information leaflet that comes withyour medication. Most information leaflets can also be found online on the Medicines and Healthcare products Regulatory Agency (MHRA) or electronic Medicines Compendium (eMC) websites. First-generation antihistamines Common side effects of first-generation antihistamines include: drowsiness impaired thinking Xerostomia dizziness constipation blurred vision an inability to fully empty the bladder (urinary retention) It's important not to underestimate the effects of antihistamine-related drowsiness. Some first-generation antihistamines can impair co-ordination, reaction times and judgement in the same way that alcohol consumption can. Therefore you shouldn't drive oruse power tools or heavy machinery after taking a first-generation antihistamine. Less common side effects of first-generation antihistamines include: insomnia (difficulty sleeping) nightmares hallucinations (seeing or hearing things that aren't real) itchy skin Rare side effects of first-generation antihistamines include: rapid heartbeat chest tightness Contact your GP if you experience these rare side effects. Side effects in children Childrenhave a greater risk ofside effects from first-generation antihistamines, particularly drowsiness and impaired thinking. Second- or third-generation antihistamines Second- or third-generation antihistamines are less likely to cause drowsiness. If you find yourself feeling drowsy, don't drive, drink alcohol, or use tools or machines. Other side effects of second- or third-generation antihistamines include: headache dry mouth dry nose feeling sick These side effects don't usually last long and should pass quickly. Rarer side effects include: rapid heartbeat chest tightness However, second- and third-generation antihistamines have been found to have less risk of heart problems than first-generation antihistamines. Contact your GP if youexperience these rare side effects. H2 receptor antagonists Antihistamines used to treat stomach ulcers are known as H2 receptor antagonists. Side effects of this type of antihistamine are uncommon but may include: diarrhoea headache dizziness skin rashes tiredness Yellow Card Scheme The Yellow Card Scheme allows you to report suspected side effects from any type of medicine you're taking. It's run by a medicines safety watchdog called the Medicines and Healthcare products Regulatory Agency (MHRA). See the Yellow Card Scheme website for more information.