What are the side effects of long term Benadryl usage in women?

The retrieved studies do not directly answer the question about long-term Benadryl use in women, but they point to real risks that apply to anyone using it chronically.

The evidence here is thin for the specific question. The search found no long-term human studies on women taking diphenhydramine for months or years. What it did find are acute and animal studies that flag mechanisms of harm. One study in infant rats showed that diphenhydramine prolonged seizure duration during electroshock, a proconvulsant effect not seen with newer antihistamines [5]. Another study measured its anticholinergic strength: diphenhydramine has a pA2 value of 6.3, meaning it blocks acetylcholine receptors at the doses people take, which is the mechanism behind confusion, dry mouth, constipation, and urinary retention [4]. A single overdose case showed the drug concentrates heavily in reproductive tissues—73 µg/g in prostate tissue versus 4.9 µg/mL in blood—which raises a question about accumulation in women's reproductive organs that no study here answers [1].

The cognitive risk is real but the evidence is mixed. One study found diphenhydramine 50 mg caused a -1.36 point drop on a memory test, less than oxybutynin but still measurable [2]. Another study found no significant memory impairment from diphenhydramine at 25 or 50 mg, despite sedation [3]. The difference may be dose, duration, or individual susceptibility—the literature does not settle it.

The bottom line: chronic Benadryl use carries well-documented anticholinergic risks (dementia, constipation, falls) that the broader medical literature supports, but this specific search found no long-term safety data in women. The evidence that does exist comes from single-dose studies in mixed populations or animal models. A woman taking it nightly for sleep or allergies is taking a drug with known cognitive and anticholinergic harms, and the studies that would quantify her personal risk over years have not been run.

My call: the evidence is too thin to give a precise risk estimate for long-term use in women, but the mechanisms of harm are real and the drug should not be used chronically. Confidence: moderate.