Certain groups of people, such as the very young, the very old, the very sick, and pregnant and breastfeeding women, are more vulnerable to harm from drugs, including OTC drugs. When such people use drugs, special precautions, which may include a doctor's supervision, should be taken.
To avoid dangerous drug-drug interactions, people should consult a pharmacist or doctor before they take prescription drugs and OTC drugs at the same time. People who have chronic disorders should also consult a pharmacist or doctor. OTC drugs are not designed to treat serious disorders and can make some disorders worse. An unanticipated reaction, such as a rash or insomnia, is a signal to stop taking the drug immediately and obtain medical advice.
Children's bodies metabolize and react to drugs differently from the way adults' bodies do. A drug may be used by many people for many years before its hazards to children are discovered. For example, many years passed before researchers confirmed that the risk of Reye's syndrome was linked to the use of aspirin in children who had chickenpox or influenza. Doctors and parents alike are often surprised to learn that most OTC drugs, even those drugs with recommended dosages for children, have not been thoroughly tested in children. The effectiveness of some cough and cold remedies is unproved, especially in children, so that giving these drugs to children may unnecessarily expose them to harmful effects of a drug and may be a waste of money.
Giving a child a correct drug dose can be tricky. Although children's doses are often expressed in terms of age ranges (for example, children aged 2 to 6 or 6 to 12), age is not the best criterion. Children can vary greatly in size within any age range, so experts advise using the child's weight to determine doses of OTC drugs.
If the label does not give instructions on how much drug to give the child, a parent should not guess. When in doubt, a parent should consult a pharmacist or doctor. Such consultation may prevent a child from receiving a dangerous drug or a dangerously high dose of a potentially helpful drug.
Many drugs for treating children come in liquid form. Even though the label should give clear guidelines about the dose, a child may be given the wrong dose because the adult in charge uses an ordinary teaspoon. The only kitchen spoons accurate enough to measure liquid drugs are measuring spoons. However, a cylindrical measuring spoon is far better for measuring a child's dose, and an oral syringe is preferred for measuring and squirting a precise amount of drug into an infant's mouth. The cap should always be removed from the tip of an oral syringe before use. A child can choke if the cap is accidentally propelled into the windpipe. Sometimes, drugs intended for treating children come with a measuring device packaged with the product. If so, the device that is in the package should be used to measure the appropriate dose.
Several children's drugs are available in more than one form. Adults must read labels carefully every time a new children's drug is used.
Normal aging changes the speed and ways in which the body metabolizes drugs (see Aging and Drugs), and older people tend to have more diseases and to take more than one drug at a time. For these reasons, older people may be more likely than younger ones to experience side effects or drug interactions. More and more prescription drug labels specify whether different doses are needed for older people, but such information is rarely included on OTC drug labels.
Many OTC drugs are potentially hazardous for older people. The risk increases when drugs are taken regularly at the maximum dose. For example, an older person who has arthritis may frequently use an analgesic or anti-inflammatory drug, with potentially serious consequences, such as a bleeding peptic ulcer. Such an ulcer is life threatening for an older person and can occur without warning.
Antihistamines, such as diphenhydramine, also pose special risks for older people. Many nighttime pain relief formulas, cough and cold remedies, allergy drugs, and sleep aids contain antihistamines. Antihistamines may worsen some disorders common among older people, such as closed-angle glaucoma and an enlarged prostate gland. They can also make a person dizzy or unsteady, leading to falls and broken bones. Antihistamines, particularly at a high dose or in combination with other drugs, can sometimes cause blurred vision, light-headedness, dry mouth, difficulty with urination, constipation, and confusion in older people.
Older people may be more susceptible to the possible side effects of antacids. Antacids that contain aluminum are more likely to cause constipation, and antacids that contain magnesium are more likely to cause diarrhea and dehydration.
During visits to the doctor, older people should mention all OTC products they are taking, including vitamins, minerals, and medicinal herbs. This information helps the doctor evaluate the entire drug regimen and determine whether or not an OTC drug may be responsible for certain symptoms.
Pregnant and Breastfeeding Women
Drugs can move from a pregnant woman to her fetus (primarily through the placenta see Drug Use During Pregnancy), and drugs can be transmitted through breast milk to the baby. Some such drugs can affect or harm the fetus or baby, so pregnant women and breastfeeding women should consult their doctor or pharmacist before taking any OTC drug or medicinal herb. OTC drug labels should be checked because they contain warnings against use during pregnancy and breastfeeding, if applicable.
Certain types of drugs are particularly problematic. They include antihistamines (commonly contained in cough and cold remedies, allergy drugs, motion sickness drugs, and sleep aids) and nonsteroidal anti-inflammatory drugs (NSAIDs). NSAIDs should not be used during the last 3 months of pregnancy unless specified by a doctor, because they may cause problems in the fetus or complications during delivery.
People With Chronic Disorders
A number of chronic disorders can become worse if an OTC drug is taken inappropriately. Because OTC drugs are intended primarily for occasional use by people who are essentially healthy, people who have a chronic or serious disorder or who plan to take an OTC drug every day should consult a health care practitioner before they purchase OTC products. In such cases, drug use is beyond the normal boundaries of self-care and requires the advice of an expert.
Many people neglect to mention their use of OTC drugs to their doctor or pharmacist. Drugs taken intermittently, such as drugs for colds, constipation, or an occasional headache, are mentioned even less often. Health care practitioners may not think of asking about use of OTC drugs or medicinal herbs when they are prescribing or dispensing a prescription. Yet many OTC drugs and medicinal herbs can interact adversely with a wide range of drugs (see Factors Affecting Response to Drugs: Drug Interactions).
Some of these interactions can be serious, interfering with the effectiveness of a drug or causing side effects. For example, taking aspirin with the anticoagulant warfarin can increase the risk of abnormal bleeding. An antacid containing aluminum or magnesium can reduce the absorption of digoxin, taken for heart disease. Taking a multiple vitamin and mineral supplement can interfere with the action of some prescription drugs. For example, the antibiotic tetracycline may be ineffective if swallowed with a product that contains calcium, magnesium, or iron.
OTC drug-drug interactions have not been studied systematically. Many serious problems have been discovered accidentally, after side effects or deaths were reported. Even when interaction warnings are printed on the label for OTC drugs, the language may be meaningless to most people. For example, the labels of some cold remedies that contain pseudoephedrine caution against using the product with a monoamine oxidase inhibitor (MAOI—given for depression) or during the 2 weeks after discontinuing the MAOI. For the many people who do not know that the antidepressant they are taking is an MAOI (such as phenelzine and tranylcypromine), this important warning is not helpful.
The best way to reduce the risk of drug-drug interactions is to ask the pharmacist to check for them. Additionally, the doctor should be told about all drugs being taken, both prescription and OTC.
Another potential problem is drug overlap. OTC products used to treat different problems may contain the same active ingredient. Unless people read the labels on everything they take, they can accidentally overdose themselves. For example, a person who takes a sleep aid and a cold remedy, both of which contain diphenhydramine, may take double the dose considered safe. Many products contain acetaminophen. A person who simultaneously takes two different products that contain acetaminophen—one for a headache and another for allergies or sinus problems—may exceed the recommended dose.
Last full review/revision April 2007 by Daniel A. Hussar, PhD