I have heard many times that the widely used antihistamines are not considered to be psychoactive drugs. Yet their impact on ones cognitive functions can be substantial. According to some sources, sedatives are also attributed being psychoactive, but not antihistamines. What is the difference?


Some links for the "cognitive effects" that I am referring to include hallucinations as well as drowsiness, anxiousness and irritability.

Besides that, it is well known that antihistamines cause drowsiness and sleepiness which are artificially altered states of mind because they are 1) not naturally-occuring, 2) have different mechanics and flow than their natural counterparts.

from experience I know these effects can be very strong, up to the state when one sees dreams while being awake. I can't find any scientific papers on that, but I have found many reports on the web and among people I've talked to.

  • $\begingroup$ When you say "their impact on ones psyche functions", what effect(s) are you talking about? $\endgroup$
    – naught101
    Nov 10 '15 at 23:57
  • $\begingroup$ @naught101 please see the update $\endgroup$
    – noncom
    Nov 11 '15 at 1:40
  • 1
    $\begingroup$ Your links list kind of broke. format them like [link name](http://...). Can you actually mention the effect in the question as well, so people know what you're talking about without going digging? $\endgroup$
    – naught101
    Nov 11 '15 at 2:37
  • $\begingroup$ @naught101 that's strange, on my side the links are working. I don't know what else can I do with them. Also, please read the update, I have been more specific on the effect in there. $\endgroup$
    – noncom
    Nov 11 '15 at 2:51
  • 1
    $\begingroup$ I fixed the two references, and removed the dictionary and yahoo answers link, because they didn't relate to antihistamines. $\endgroup$
    – naught101
    Nov 11 '15 at 4:04

Short answer
First-generation anti-histamines are psychoactive, second-generation equivalents may not be*.

According to WHO, psychoactive substances are:

[...] substances that, when taken in or administered into one's system, affect mental processes, e.g. cognition or affect. This term and its equivalent, psychotropic drug, are the most neutral and descriptive term for the whole class of substances, licit and illicit, of interest to drug policy. ‘Psychoactive’ does not necessarily imply dependence-producing, and in common parlance, the term is often left unstated, as in ‘drug use’ or ‘substance abuse’.

Antihistamines are used to treat allergies. First-generation antihistamines readily cross the blood-brain-barrier and have been associated with performance deficits on tests of attention, working memory, vigilance, and speed. By contrast, second-generation antihistamines that do not readily reach the brain do not have these side-effects (Kay, 2000).

Since attention, working memory and vigilance are mental cognitive processes, first-generation antihistamines fall into the classification of WHO as being psychoactive.

- Kay, J Allergy Clin Immunol (2000); 105(6-2): S622–7

*I am not an MD and data on 2nd generation drugs are based on a single study with a limited number of tests. Consult a medical professional for prescription of the appropriate treatment.

  • $\begingroup$ Yes, I follow the medical advice of doctors - having seasonal hay fever since I was a child. But they don't say anything except "take this". So, from the answer, at least, it is clear that AHs do fall under the category officially, although somehow nobody mentions it for some reason. Gen-I force people sleep and forget (too strong). Gen-II surely have psychoactive effects too and allow to stay sober enough to experience it. The prolonged use seems to change personality, giving access to moods and thoughts not availbale without them. It's just that I am so surprised there's so little research. $\endgroup$
    – noncom
    Nov 20 '15 at 12:55
  • $\begingroup$ @noncom - my apologies for the note, but self-help questions are explicitly off-topic here. It's a miracle you question survived in the first place :) $\endgroup$
    – AliceD
    Nov 20 '15 at 12:59
  • $\begingroup$ Yes, I know, it looks like the question managed to be as impersonal as it could :) medical topics are very different in that from the technical ones... As for the matter - I see, really there's not much else to say, since nobody really went into researching this. Even MAPS does not pay any attention to it. But I believe AHs (and I mean gen-II too, azelastine, cetirizine) can influence people strongly, especially in long-term use, especially children and people with unusual mental conditions.. Well, maybe some time in the future someone will do more research.. $\endgroup$
    – noncom
    Nov 20 '15 at 17:59

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