[15][22] Unlike earlier-generation antihistamines, loratadine is considered largely free of antimuscarinic effects (urinary retention, dry mouth, blurred vision).

[23][24] Substances that act as inhibitors of the CYP3A4 enzyme such as ketoconazole, erythromycin, cimetidine, and furanocoumarin derivatives (found in grapefruit) lead to increased plasma levels of loratadine — that is, more of the drug was present in the bloodstream than typical for a dose.

[25] Antihistamines should be discontinued 48 hours before skin allergy tests, since these drugs may prevent or diminish otherwise positive reactions to dermal activity indicators.

[15] Loratadine is a tricyclic antihistamine, which acts as a selective inverse agonist of peripheral histamine H1 receptors.

[35] Schering-Plough developed loratadine as part of a quest for a potential blockbuster drug: a nonsedating antihistamine.

[36] However, terfenadine had to be removed from the U.S. market by the manufacturer in late 1997 after reports of serious ventricular arrhythmias among those taking the drug.

In 1998, in an unprecedented action in the United States, an American insurance company, Anthem Inc., petitioned the federal Food and Drug Administration to allow loratadine and two other antihistamines to be made available over the counter (OTC) while they were still protected by patents; the administration granted the request, which was not binding on manufacturers.

[41] In 2017, loratadine was available under many brand names and in many forms worldwide, including several combination drug formulations with pseudoephedrine, paracetamol, betamethasone, ambroxol, salbutamol, phenylephrine, and dexamethasone.

The federal Food and Drug Administration responded with strong regulations requiring disclosure of side effects and other information.

These rules made pharmaceutical manufacturers balk at spending money on ads that had to highlight negative aspects.

"[43][44] The first ads made people aware of the brand and increased prescriptions, which led Schering-Plough and others to aggressively pursue the advertising strategy.

The book, written by PRIEST, penciled by Joe Staton, and inked by Mike DeCarlo, sees Tim Drake unable to perform his crime-fighting duties because hay fever and antihistamines make him drowsy.

[43] Instead of including the "brief summary" that took up a full page in magazine ads and would take too long to explain in a short television advertisement, drug makers were allowed to refer viewers to print ads, informative telephone lines, and websites, and to urge people to talk to their doctors if they wanted additional information.