I've never liked the fact that Moms use anything, including Benadryl, to put their kids to sleep, especially for the parent's convenience. But I hear it all the time!
I'm in psych now, and over the past 35 years as a nurse, I've worked in a Children's Hospital ER (trauma and walk-in), on a peds medical floor, in Labor/Delivery, and several walk-in clinics.
During this time, I've seen Benadryl used for so many different things...
insomnia (sleeplessness), allergic reactions, with-drawal symptoms, itching, anxiety, cold/allergy symptoms, etc.
Benadryl has always been my "miracle med" because it has so many uses, is non-addicting, is fast-acting,
and can now be obtained "over the counter". (In the "olden days", it was by 'script only.)
BUT... if used on a daily/regular basis, one can build up a tolerance for it.
(It will eventually take higher doses to be effective).
AND... Benadryl can have a reverse effect on some patients.
The patient becomes more restless, more awake, jittery, hyper-verbal, paranoid, manic, etc.
At that time, no amount of Benadryl would be effective.
I've seen many times where tolerance or a reverse effect developed and the Mother overdosed her child...
or worse, used something much stronger to put her child to sleep.
Because Casey seemed so desperate (the phone calls) and continued to go out and party (the photos)...
I could definitely see her trying
anything to get Caylee to calm down and/or go to sleep, thus overdosing her.