Anti-histamines

It depends on which medication you took. Some antihistamines can make you very sleepy, others, not so much. As a child, they sent my youngest sky high! I’d have to try and scrape her off the ceiling to get her to bed.

This is common, especially in people age 65+. As we age, our bodies becomes less efficient at metabolizing medications, so they can have greater effects. In addition, the blood brain barrier also becomes less effective, so any medication that affects the brain can become more potent.

I didn’t realise how different many antihistamines were. I just used to look at what it said on the packet ie non drowsy or drowsy. But then I googled it and it isn’t as strait forward as that. Some are fast acting. Some slow. Some affect you for a short while, others for a long time. Non drowsy aren’t necessarily non drowsy either. I made a list of them but even that confuses me. It’s the same with cold and flu medication. Some of them will keep you awake all night and some send you to sleep.

This tells me to read the packet!
Like MayBee I thought it came down to «drowsy» ( eg Piriton and great for a good night’s sleep ) and the rest!
That‘ll larn me as Badger said

I always take the drowsy antihistamines at bedtime when in a different time zone, they really help to sort out jet lag.

A medic acquaintance^ recommended life hack

Non-Drowsy (Second/Third-Generation): These target peripheral histamine receptors without crossing easily into the brain, making them ideal for daytime use. Common options include:Cetirizine: (e.g., Zirtek, Reactine)Loratadine: (e.g., Claritin)Fexofenadine: (e.g., Allegra, Telfast)Drowsy (First-Generation): These are older, effective formulas that readily cross the blood-brain barrier. Because they induce sleep, they are sometimes useful for nighttime symptom relief, motion sickness, or insomnia. Common options include:Diphenhydramine: (e.g., Benadryl)Chlorphenamine: (e.g., Piriton)Promethazine: (e.g., Phenergan)

I end up longterm on Cetrizine, fexofenadine or loratitine, as I have allergy fatigue in the summer. None make me drowsy in the least, & sometimes I take a double dose because I can't remember if I took them first thing, & if I skip a day I suffer for a week.(then I really am sleepy)
So that tallies with wht you've found, Maybee70.

AntihistamineActive IngredientHow fast does it work?Will it make your sleepy?For how long is it effective?
BenadrylAcrivastineLess than 15 minsGenerally non-drowsy, but can cause drowsiness.Less than 8 hours
PiritonChlorphenamine maleate30-60 minsVery likely to cause sleepiness.4-6 hours
CetirizineCetirizine30-60 minsLess likely to make you drowsy.12-24 hours
FexofenadineFexofenadineLess than 60 minutesNo.24 hours
ClaritynLoratadine1-3 hours.No.24 hours

I have to take anti - histamines for hay fever and urticaria -
they give ne some relief.
Without them I'm miserable.
But they can send me to asleep if I'm not
careful as to what time I take them.

I usually take them at night .

Cetirizine30-60 minsLess likely to make you drowsy.12-24 hours
Oh dear, that seems to be the principal ingredient of what I took - Benadryl .
Goodness knows what the others might do to me.
Better just put up with the sneezing.

I remember the first time I took Cetirizine. I woke up one morning and on looking in the bathroom mirror saw lumps appearing which spread all over me. Going straight to the doctors ( that was in the days when you could walk into a surgery and get an appointment) I was given a box of Zirtek. I was amazed at how they worked straight away and the lumps disappeared as fast as they’d sprung up. It was like a miracle.

MawsRosie

This tells me to read the packet!
Like MayBee I thought it came down to «drowsy» ( eg Piriton and great for a good night’s sleep ) and the rest!
That‘ll larn me as Badger said

I always carry Piriton with me after my last dog was stung by a wasp and had an awful reaction to it. The vet prescribed Piriton one tablet twice a day. And to shower her in cold water but as it was winter time and very cold I wouldn’t do that.

I avoid anti-histamines. Not only do they have the saame ffect on me as an overdose of Mogadon. They also cause massive constipation.