Sulfur dioxide, an acidic pollutant, irritates the respiratory tract. It causes violent coughing when it irritates the throat, and may result in shortness of breath, lung edema, and pneumonia when it reaches the lungs.

Both ozone and nitrogen oxides are oxidizing pollutants. Like sulfur dioxide, they cause respiratory irritation; ozone and nitrogen oxides, however, tend to be more irritating to the lung than to the upper respiratory tract.

Carbon monoxide, an asphyxiating pollutant, binds to hemoglobin more strongly than oxygen does. Such binding produces a hemoglobin molecule that cannot carry its normal load of four oxygen molecules. In addition, once carbon monoxide is bound, the hemoglobin molecule does not as readily release to the tissues the oxygen molecules already bound to it. Therefore, tissues lack oxygen, resulting in many toxic effects. Because the brain is especially sensitive to the lack of oxygen, most of the symptoms are neurological. Lack of oxygen is termed asphyxiation, and thus carbon monoxide is an asphyxiant.

Painkillers

Painkillers (analgesics) are the most commonly used drugs and account for many poisoning cases. Examples include aspirin and acetaminophen. Aspirin interferes with the oxidative burning of fuel by cells. To get energy, the cells switch to a less efficient way of burning fuel that does not use oxygen but generates a lot of heat. Increased perspiration develops to counteract a rise in body temperature, leading to dehydration and thirst. Aspirin also alters the pH in the body, affecting the central nervous system (Table 3). The major toxicity of acetaminophen is liver damage.

The major toxicity from narcotic analgesics, like morphine, is depression of the central nervous system, especially the brain centre controlling respiration. The cause of death in morphine overdoses is usually respiratory failure. Nausea is caused by morphine’s stimulation of the chemoreceptor trigger zone in the brain, and constipation is caused by morphine’s depression of muscular activity in the intestine (Table 3).

Tranquilizers and sleeping pills

Benzodiazepines, such as diazepam, clonazepam, and chloridazepoxide, have a wide margin of safety when used at prescribed doses. Their major toxic effect is depression of the central nervous system, which results in muscular incoordination and slurred speech (Table 3). For sleeping pills containing barbiturates, chloral hydrate, paraldehyde, and meprobamate, however, the margin of safety is much narrower, and the major toxicity is severe depression of the central nervous system, leading to respiratory and cardiovascular failure (Table 3).

Antipsychotic drugs

Like benzodiazepines, antipsychotic drugs such as chlorpromazine, perphenazine, and haloperidol have a relatively large therapeutic index, rarely causing fatalities. They occasionally may block the action of the parasympathetic and sympathetic nervous systems and thus produce such undesired effects as dry mouth and blurred vision from the former and a drop in blood pressure upon standing in the latter (Table 3).

Cold medications

Nasal decongestants, antihistamines, and cough medicine, which are found in over-the-counter preparations for treating the symptoms of colds, have a low potential to produce toxicity. Nasal decongestants, such as ephedrine, mimic the action of epinephrine by stimulating the sympathetic nervous system, and consequently, an overdose of ephedrine produces symptoms related to stimulation of the sympathetic and central nervous systems (Table 3). Depression of the central nervous system and parasympathetic blockade are two common toxicities of antihistamines such as diphenhydramine (Table 3). Depression of the central nervous system is also the major toxicity of dextromethorphan and codeine, both used to suppress coughing.

Antiseptics

Most antiseptics (e.g., hydrogen peroxide, benzoyl peroxide, resorcinol, benzalkonium chloride, parabens, and cetylpyridinium chloride) produce gastrointestinal irritation if ingested (Table 3). Benzoyl peroxide and parabens applied to the skin may be toxic. Among the most toxic antiseptics are hexachlorophene, benzalkonium, and cetylpyridinium chloride, any of which can cause injuries to internal organs. Systemic toxicity (double vision, drowsiness, tremor, seizures, and death) with hexachlorophene is more likely to occur in babies because the relatively thin stratum corneum of their skin is highly permeable.

Vitamins and iron pills

Deficiencies as well as excesses of vitamins are harmful. Excessive vitamin A (retinol, or retinoic acid), known as hypervitaminosis A, can result in skin lesions, edema, and liver damage. Overconsumption by Alaskan natives of polar bear liver, a rich source of vitamin A, has produced acute toxicities, characterized by irresistible sleepiness and severe headaches. Chronic poisoning with vitamin A can cause neurological symptoms, including pain, anorexia, fatigue, and irritability (Table 3).

Excess vitamin C can lead to kidney stones. Apart from irritation of the skin and respiratory tract, the most severe toxicity of vitamin K excess is the increased destruction of red blood cells, which leads to anemia and the accumulation of bilirubin, one of the products of hemoglobin degradation (Table 3). Excess bilirubin can result in brain damage in newborns, a condition known as kernicterus. Because the blood–brain barrier is not well developed in newborns, bilirubin enters and damages the brain. Due to the blood–brain barrier, kernicterus is not seen in adults.

Iron, a metal that is necessary for normal health, can also cause poisoning. The toxicity of iron is a result of its corrosive action on the stomach and intestine when present in high concentrations. As a result, intestinal bleeding occurs, which can lead to the development of shock.

Antidepressants

Among tricyclic antidepressants, amitriptyline and imipramine account for most of the fatal cases of poisoning. These drugs have a number of effects, including blockage of the parasympathetic system and damage to the central nervous system, the latter producing symptoms such as fatigue, weakness, lowered body temperature, seizures, and respiratory depression (Table 3). Death is usually caused by damage to the heart. Lithium salts, used to treat manic depression, have a relatively low therapeutic index.