The two Advil PM strengths are the same drug in a different salt
The Liqui-Gels carry 25 mg of diphenhydramine hydrochloride, the caplets 38 mg of the heavier citrate. Two units at bedtime is about 43.8 mg or 43.4 mg of the drug itself.
What the study found
Two boxes of the same product print 25 mg and 38 mg
The difference is the salt, not the drug. Advil PM Liqui-Gels carry 25 mg of diphenhydramine hydrochloride per capsule. The caplets carry 38 mg of diphenhydramine citrate, a heavier molecule. Two units at bedtime either way is about 43.8 mg and 43.4 mg of diphenhydramine itself.
The caveat · Worked out, not printed on the box
The two milligram figures are worked out from published molecular weights rather than quoted from a label, so they are close but should not be treated as an exact conversion factor. Both label versions were read on 6 September 2026, and printed strengths do change.