Susan asked
If you have had a reaction to doxylamine (such as agitation, and sleeplessness) and want to try diphenhydramine, could you have the same reaction? I have taken NyQuil and have really bad allergies and want to take Benadryl at night.
At a glance
- Benadryl (diphenhydramine) and doxylamine (one of the ingredients in NyQuil) are both first-generation ethanolamine antihistamines.
- Although uncommon, first-generation antihistamines can sometimes cause restlessness and agitation. This is sometimes known as 'paradoxical excitation'.
- Due to their similarity, having side effects to one likely puts you at a higher risk of experiencing side effects from the other.
Answer
If you had an adverse reaction to doxylamine, it is very possible you will have a similar experience with diphenhydramine.
This is because both are first-generation antihistamines and are very similar to one another in terms of chemical structure and effect.
They are both in the ethanolamine class of antihistamines, which are noted for their relatively short duration of action and sedating properties (which is why they are used in over the counter night-time sleep aids).
While it isn't a 'sure thing' you will have a reaction to both, your risk is certainly greater.
The reaction you had to doxylamine (agitation and sleeplessness) is a relatively uncommon side effect of first-generation antihistamines but is well known nonetheless. It is sometimes described as an 'inner-restlessness' where you feel as though you need to move parts of your body to regain comfort. The side effect has also been referred to as 'paradoxical excitation'.
It is far more common in children but certainly can happen in adults too...typically when higher doses are used. Also, some studies suggest (with diphenhydramine at least) that certain individuals who metabolize the drug more quickly (CYP2D6 ultrarapid metabolizers) may be more at risk.
Having said all this, even though doxylamine and diphenhydramine are very similar, they are unique chemical compounds and produce different metabolites as our bodies process them.
So, if you have had a feeling of agitation with doxylamine (which is in NyQuil), it may happen with Benadryl (diphenhydramine) too, but it's tough to tell how likely this is to happen.
If you wanted to try diphenhydramine, it would be recommended to start at a low dose and assess your tolerability.
You mention allergies in your question. If you are taking Benadryl just for allergies, it may be more prudent to try a second-generation antihistamine (e.g. Claritin, Zyrtec, Allegra, or Xyzal) instead for longer coverage and fewer sedative side effects.
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