If i had a drink 6-7 hours ago is it safe to take benadryl (diphenhydramine)?

Depends on amount: It depends on the size of the drink and the type of drink. If it was one drink and if the definition on that drink is 12 ounces of regular beer, which is usually about 5% alcohol or 5 ounces of wine, which is typically about 12% alcohol or 1.5 ounces of distilled spirits, which is about 40% alcohol. Then about 7 hours should be long enough for you to take a Benadryl (diphenhydramine).

Yes: It should have gone long enough if you had just one drink. If you are/were intoxicated, then hold off.

Don't exceed dosage: probably safe if you just had one drink, and not exceeding recommended dose for benadryl, (diphenhydramine) don't drive as well, good luck