Claritin’s active ingredient is loratadine, a second-generation antihistamine that blocks allergic reactions without causing significant drowsiness. Each standard Claritin tablet contains 10 mg of loratadine along with a short list of inactive ingredients. But “Claritin” covers several different products, and the ingredients vary depending on which version you pick up.
The Active Ingredient: Loratadine
Loratadine is what makes Claritin work. It’s a histamine blocker, meaning it competes with histamine for the same receptors on your cells. When your immune system overreacts to pollen, pet dander, or dust mites, it floods your body with histamine. Histamine latches onto receptors in your nose, throat, skin, and lungs, triggering the familiar cascade of sneezing, itching, runny nose, and watery eyes. Loratadine gets to those receptors first and blocks histamine from binding, which prevents those symptoms from ramping up.
Specifically, loratadine targets receptors on blood vessels, airway muscles, gut cells, and immune cells. By blocking histamine at blood vessels, it reduces the swelling and flushing that cause congestion. At airway muscles, it helps keep breathing passages relaxed. And at nerve endings in the skin and nasal passages, it dials down itching and pain signals.
The reason Claritin rarely makes you drowsy, unlike older antihistamines such as Benadryl, is that loratadine barely crosses into the brain. A natural pump in the blood-brain barrier actively pushes it back out, so it stays working in your body without affecting alertness. Your liver breaks loratadine down into an active byproduct called desloratadine (sold separately as Clarinex), which continues blocking histamine as the original drug is processed.
Inactive Ingredients in Standard Tablets
The standard Claritin 10 mg tablet has a remarkably simple inactive ingredient list: corn starch, lactose, and magnesium stearate. Corn starch acts as a filler and helps the tablet break apart in your stomach. Lactose is a common tablet binder and filler. Magnesium stearate is a lubricant that prevents the powder from sticking to manufacturing equipment.
One detail worth noting: standard Claritin tablets do contain lactose. If you have a significant lactose intolerance or a milk allergy, the amount in a single tablet is small, but it’s there. The tablets do not list any gluten-containing ingredients, though they aren’t formally certified gluten-free.
Claritin RediTabs
Claritin RediTabs are orally disintegrating tablets designed to dissolve on your tongue without water. They contain the same 10 mg of loratadine but use a completely different set of inactive ingredients: anhydrous citric acid, gelatin, mannitol, and mint flavor. Mannitol is a sugar alcohol that creates the tablet’s texture and helps it dissolve quickly. Gelatin gives the tablet structure. These tablets are lactose-free, making them an alternative if lactose is a concern, but they do contain gelatin, which is animal-derived.
Children’s Claritin Syrup
The liquid formulation designed for kids contains loratadine at a lower concentration (typically 1 mg per mL) suspended in a flavored syrup base. The grape-flavored version includes sorbitol, maltitol, glycerin, sucralose, sodium benzoate, propylene glycol, phosphoric acid, monobasic sodium phosphate, edetate disodium, purified water, and grape flavoring.
This formulation is sugar-free, relying instead on sorbitol, maltitol, and sucralose for sweetness. Sorbitol and maltitol are sugar alcohols that can cause digestive discomfort in some children if consumed in larger amounts, though the quantity in a single dose is minimal. Sodium benzoate serves as a preservative. There’s no lactose or gelatin in the liquid version.
Claritin-D: A Different Product
Claritin-D is not just Claritin in a different box. It contains two active ingredients: loratadine plus pseudoephedrine, a nasal decongestant. The 24-hour version packs 10 mg of loratadine and 240 mg of pseudoephedrine sulfate into a single extended-release tablet. A 12-hour version is also available with a lower pseudoephedrine dose per tablet, taken twice daily.
Pseudoephedrine works differently from loratadine. It narrows blood vessels in the nasal passages, reducing swelling and congestion directly. This is why Claritin-D is kept behind the pharmacy counter in the United States, even though it doesn’t require a prescription. You’ll need to show ID to purchase it, because pseudoephedrine is a regulated ingredient. If you’re only looking for an antihistamine without a decongestant, standard Claritin is what you want.
How Loratadine Works in Your Body
After you take a Claritin tablet, loratadine is absorbed through your digestive tract and reaches your bloodstream. Your liver then processes it extensively, using two enzyme pathways (CYP 3A4 and 2D6) to convert it into desloratadine. Both the original loratadine and desloratadine are active against histamine, which is part of why the drug provides a full 24 hours of relief from a single dose.
Because the liver plays such a central role in processing loratadine, anything that affects those same liver enzymes can change how the drug behaves. Grapefruit juice and certain medications use the same enzyme pathways, which could potentially alter how quickly or slowly your body clears loratadine.
Comparing Formulations at a Glance
- Standard tablet: Loratadine 10 mg, with corn starch, lactose, magnesium stearate. Contains lactose.
- RediTabs: Loratadine 10 mg, with citric acid, gelatin, mannitol, mint flavor. Lactose-free but contains gelatin.
- Children’s syrup: Loratadine 1 mg/mL, with sorbitol, maltitol, sucralose, and other liquid-base ingredients. Sugar-free, lactose-free, gelatin-free.
- Claritin-D 24-hour: Loratadine 10 mg plus pseudoephedrine sulfate 240 mg. Sold behind the pharmacy counter.
Generic loratadine tablets are widely available and contain the same active ingredient at the same dose. The inactive ingredients in generics may differ slightly from brand-name Claritin, so if you have a sensitivity to a specific filler or binder, it’s worth checking the label on whichever version you buy.