Certain episodes (such as "3", "Never Again", "Milagro" and "Avatar") feature occasional sex scenes (actions, no nudity), in general once or perhaps twice per season. Characters on a few occasions in stages of undress, rarely though in a sexual nature (more sleeping, occasional bathing interruptions) and prostitutes occasionally crop up, as spies, information sources etc. The episode "The Jersey Devil" features a naked Neanderthal woman, though we never see any nudity beyond one quite distant hazy rear shot. The episode "Excelsis Dei" revolves around a woman who was raped by supernatural entities, she is shown thrashing around in a bed (fully covered) and later seen badly bruised and mentally scarred from the ordeal. The episode "Home" revolves around a family resulted from years of incest.
Most violence in this series is off-screen, but injury detail occasionally intense with some close-ups of corpses, injuries, blood and on a few occasions gore. Certain episodes (such as "Red Museum", "Paper Hearts", "Revelations", "Sein und Zeit", "Oubliette" and "Invocation") deal with topics of pedophilia and child murder.
Although profanity is infrequently used, occasionally it is no more intense than would be heard on network television now.
Although drug, alcohol, and tobacco use are not glorified nor endorsed, sometimes characters drink and smoke socially, however one recurring character dubbed 'The Cigarette Smoking Man' is seen smoking in virtually every scene he is in. In 'War of the Coprophages' teenagers are depicted to be high on some home-brewed, meth-like concoction.
Luckily IMDB includes the official ratings below so no need to break the rules and add opinionated scores.