Who should not take diphenhydramine?

Diphenhydramine should never be taken by someone who has taken a monoamine oxidase inhibitor (MAOI) within the last 14 days. This could cause a very serious interaction. Someone with hyperthyroidism, asthma, hypertension, enlarged prostate, stomach ulcers or glaucoma may not be able to take diphenhydramine or may require a lower dose and monitoring, while taking the medication. This medication may cause increased side effects in older people, so they also may want to take a lower dose of diphenhydramine. Children under four years of age should never take this drug, unless prescribed by a doctor. Children between four and 11 years of age should follow the directions on the drug package label. Someone who is allergic to diphenhydramine should never take it. It should not be used while breastfeeding.