[7][3] Side effects include sleepiness, dizziness, headache, upset stomach, skin rash, hallucinations, and allergic reactions.

[10] Chewing or sucking on the capsule, releasing the drug into the mouth, can also lead to laryngospasm, bronchospasm, and circulatory collapse.

It is theorized to work by inhibiting stretch receptors in the lungs, in turn suppressing the cough reflex in the brain.

[7][5][18] Benzonatate also reduces the consistency and volume of sputum production associated with cough in those with chronic obstructive pulmonary disease (COPD).

[8] Benzonatate acts as a local anesthetic and the liquid inside the capsule can be applied in the mouth to numb the oropharynx for awake intubation.

[7] However, there can be life-threatening adverse effects when the medication is absorbed by the oral mucosa, including choking, hypersensitivity reactions, and circulatory collapse.

[3][22][12] Procaine and tetracaine, previously used heavily in the fields of dentistry and anesthesiology, have fallen out of favor due to allergies associated with their metabolites.

[22] Similarly, severe hypersensitivity reactions to benzonatate have been reported and include symptoms of laryngospasm, bronchospasm, and cardiovascular collapse.

[22] There is a potential for these adverse effects to occur at a therapeutic dose, that is, a single capsule if chewed or sucked on in the mouth.

[22] Isolated cases of bizarre behavior, mental confusion, and visual hallucinations have been reported during concurrent use with other prescribed medications.

[3] Central nervous system effects associated with other para-aminobenzoic acid (PABA) derivative local anesthetics, for example procaine or tetracaine, could occur with benzonatate and should be considered.

[3][24] Signs and symptoms can occur rapidly after ingestion (within 15–20 minutes) and include restlessness, tremors, convulsions, coma, and cardiac arrest.

Treatment focuses on the removal of gastric contents and managing symptoms of sedation, convulsions, apnea, and cardiac arrhythmia.

[22] Toxicity above the therapeutic dose is relatively low and ingestion of a small handful of pills can cause symptoms of overdose.

[22] After absorption and circulation to the respiratory tract, benzonatate acts as a local anesthetic, decreasing the sensitivity of vagal afferent fibers and stretch receptors in the bronchi, alveoli, and pleura in the lower airway and lung.

Benzonatate is hydrolyzed by plasma butyrylcholinesterase (BChE) to the metabolite 4-(butylamino)benzoic acid (BABA) as well as polyethylene glycol monomethyl ethers.

[5] Benzonatate is a butylamine, para-amino-benzoic acid, or long-chain polyglycol, structurally related to other ester local anesthetics such as procaine and tetracaine.

[3] However, the reference standard for benzonatate is a mixture of n-ethoxy compounds, differing in the abundance of 7 to 9 repeating units, with an average molecular weight of 612.23 g/mol.

[5] Benzonatate was first made available in the United States in 1958 as a prescription medication for the treatment of cough in individuals over the age of 10.

[24][25] There is a variety of prescription opioid-based cough relievers, such as hydrocodone and codeine, but have unwanted side effects and potential of abuse and diversion.