The word antihistamines is playable in Words With Friends™, no blanks required. Because it is longer than 7 letters, you would have to play off an existing word or do it in several moves.
Words With Friends™ Letter Score: 21
Highest Scoring Words With Friends™ Plays In The Letters antihistamines
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Seven Letter Word Alert: (44 words)
amentia, amnesia, animate, animist, anthems, ashiest, asinine, atheism, atheist, attains, haemins, hastate, hastens, hinnies, imitate, inmates, inseams, instant, instate, intents, mannish, messiah, miniate, misseat, mitiest, mittens, satiate, seitans, sestina, shamans, siennas, simians, smitten, stamens, stamina, statins, statism, stimies, tannest, tenants, theisms, theists, thiamin, tiniest