Nicotine absorption through the mouth is a process where the substance enters the bloodstream directly through the tissues of the oral cavity. This method is used by smokeless products like nicotine gum, lozenges, and pouches. This form of delivery relies on the mouth’s environment to transfer nicotine into the body. The process begins when a product is placed in the mouth, initiating biological interactions that determine how much nicotine is absorbed and how quickly its effects are felt.
The Science of Buccal Absorption
The primary pathway for nicotine to enter the body through the mouth is the buccal mucosa, the soft tissue lining the cheeks and lips. This membrane is rich with tiny blood vessels, providing a direct route to the circulatory system. When nicotine contacts this surface, it passes through the membrane into the capillaries via passive diffusion. This mechanism allows nicotine to bypass the digestive system and enter the bloodstream.
The pH level inside the mouth is a determining factor in how effectively nicotine crosses the buccal membrane. As a weak base, nicotine exists in two forms: ionized (charged) and unionized (uncharged). In acidic conditions, nicotine is mostly in its ionized state, which does not easily pass through cell membranes. In a more alkaline environment, more nicotine is converted to its unionized, or “freebase,” form, which is more lipid-soluble and diffuses across membranes more efficiently.
To facilitate this process, many oral nicotine products contain buffering agents that raise the pH of the surrounding saliva. These products can elevate the mouth’s pH from around 7.0 to a more alkaline state, optimizing conditions for absorption. This pH adjustment is a design feature of oral nicotine products, ensuring sufficient nicotine is delivered into the bloodstream. Without this adjustment, much of the nicotine would remain in its less absorbable ionized form.
Factors That Influence Absorption
The type of oral product used affects the rate and amount of nicotine absorption. Nicotine gum releases its contents through the mechanical action of chewing, and the user controls the release rate by how intensely they chew. In contrast, products like lozenges and pouches release nicotine as they dissolve in saliva. A lozenge dissolves slowly for a gradual release, while a pouch offers passive delivery as it sits between the lip and gum.
Saliva acts as a solvent that dissolves nicotine from the product and distributes it throughout the mouth. The volume and circulation of saliva can impact how much of the mucosal surface is exposed to nicotine. User behaviors, such as where a pouch is placed or how often a lozenge is moved, alter absorption efficiency by changing the contact area and duration.
The product’s formulation, beyond its pH, also affects absorption. Nicotine concentration is a primary factor, as higher-dose products deliver more nicotine to the bloodstream. For example, a 4 mg nicotine gum results in higher peak blood levels than a 2 mg gum. Flavorings or other additives may also subtly impact the user experience and the mouth’s local environment.
Oral Versus Pulmonary Nicotine Delivery
The way nicotine enters the body alters its effects, with a stark difference between oral and pulmonary absorption. Pulmonary absorption, which occurs when smoking or vaping, delivers nicotine to the brain with incredible speed. After a puff, nicotine reaches the brain in as little as 10 to 20 seconds. This creates a rapid, high-concentration spike in the bloodstream, leading to an intense and immediate neurological response.
Oral absorption is a slower and more gradual process. With products like gum or lozenges, it can take up to 30 minutes to reach peak nicotine levels in the blood, which are lower than those from smoking. This results in a less intense but more sustained delivery of nicotine, avoiding the sharp peaks associated with inhalation. The slower onset means the reinforcing effect is less immediate than with smoking.
A distinction between these methods is what is delivered with the nicotine. Smoking involves combustion, which releases nicotine with tar and thousands of other harmful chemical compounds. Oral nicotine products do not involve burning and deliver nicotine without these combustion byproducts. This difference in delivery mechanism separates the exposure profiles of smoking and using oral nicotine products.
What Happens to Swallowed Nicotine
Some nicotine from oral products will inevitably be mixed with saliva and swallowed instead of being absorbed through the buccal mucosa. The amount swallowed varies by product and user habits, with a significant portion from gums and lozenges ending up in the stomach. Once swallowed, nicotine travels to the stomach, an acidic environment not conducive to absorption.
Any nicotine absorbed from the gastrointestinal tract enters the portal vein, which leads directly to the liver where it undergoes “first-pass metabolism.” The liver’s enzymes, particularly CYP2A6, immediately begin to break down the nicotine before it can enter the general circulatory system. This process metabolizes a large percentage of swallowed nicotine into metabolites like cotinine.
Consequently, the bioavailability of swallowed nicotine is low, often estimated to be around 30-40%. This means a substantial portion of ingested nicotine is inactivated by the liver on its first pass. This metabolic pathway is why oral products are designed for buccal absorption, as relying on swallowing is a far less effective method of delivery.