Over-the-counter (OTC) drugs are medicines that may be sold directly to a consumer without a prescription from a health care professional, as compared to prescription drugs, which may only be sold to consumers possessing a valid prescription. In many countries, OTC drugs are selected by a regulatory agency to ensure that they are ingredients that are safe and effective when used without a physician's care. It is important to note that OTC drugs are regulated as ingredients, not final products. By doing so governments allow manufacturers freedom to formulate ingredients, or combinations of ingredients, into proprietary mixtures. 
The term over-the-counter may be somewhat counter-intuitive, since, in many countries, these drugs are often located on the shelves of stores like any other packaged product. In contrast, prescription drugs are almost always literally passed over a counter from the pharmacist to the customer. Some drugs may be legally classified as over-the-counter (i.e. no prescription is required), but may only be dispensed by a pharmacy employee after an assessment of the patient's needs and/or the provision of patient education. In many countries, a number of OTC drugs are available in establishments without a pharmacy, such as general stores, supermarkets, gas stations, etc. Regulations detailing the establishments where drugs may be sold, who is authorized to dispense them, and whether a prescription is required vary considerably from country to country.
OTC drugs pose particular drug safety concerns as they are dispensed and used without the direction of a health care professional. Patients may combine OTC drugs with their prescription medicine, potentially causing drug interactions if the substances are incompatible. Patients may also inadvertently take multiple OTC drugs containing the same active ingredient, which could lead to an overdose or increased side-effects. In other cases, patients may take more than the recommended dose of a drug, as they may not read or understand the directions or they may choose to ignore them, believing a higher dose to be more effective.
While many OTC drugs have wide therapeutic ranges, some may pose greater risks if not used as directed. For example, acetaminophen (also known as paracetamol) is regulated as an OTC drug in many countries and is widely regarded as safe if used as directed, but it can cause acute liver failure if recommended doses are exceeded and/or when combined with alcohol. This problem is further compounded by the plethora of OTC products containing acetaminophen, as patients may inadvertently overdose by taking multiple drugs (e.g. an individual with a common cold may use two acetaminophen-containing products to treat muscle aches and fever without realizing that they contain the same active ingredient).
|Regulation of therapeutic goods in the United States|
In the United States, the manufacture and sale of OTC substances is regulated by the FDA. The Federal Food, Drug, and Cosmetic Act requires that all "new drugs" are required to obtain a New Drug Application ("NDA") prior to entering interstate commerce, but the act exempts any drugs generally recognized as safe and effective ("GRAS/E") from this requirement. In order to deal with the vast number of OTC drugs that were already on the market prior to the requirement that all drugs obtain an NDA, the FDA created the OTC monograph system to review classes of drugs and categorize them as GRAS/E after review by expert panels. This meant that certain classes of OTC drugs were not required to obtain an NDA and could remain on the market if they conformed to the monograph guidelines for doses, labeling, and warnings.
Thus, manufacture must be done either pursuant to an FDA monograph, which specifies types of OTC drugs, active ingredients and labeling requirements, or pursuant to a New Drug Application (NDA), for products which do not fit within a specific monograph. Because an NDA is extremely expensive to complete. Examples of OTC substances approveded in the USA are sunscreens, anti-microbial and anti-fungal products, external and internal analgesics such as lidocaine and aspirin, psoriasis and eczema topical treatments, anti-dandruff shampoos containing coal tar, and other topical products with a therapeutic effect.
The Federal Trade Commission regulates advertising of OTC products. This is in contrast to prescription drug advertising, which is regulated by the FDA.
The FDA requires that OTC products are labeled with an approved Drug Facts label to educate consumers about their medications. These labels comply to a standard format and are intended to be easy for typical consumers to understand. Drug Facts labels include information on the product's active ingredient(s), indications and purpose, safety warnings, directions for use, and inactive ingredients.
An ill-defined third category of substances are those products having over-the-counter status from the FDA, while being simultaneously subject to other restrictions on sale. While these products are legally classified as OTC drugs, they are typically stored behind the pharmacy counter and are only sold in stores employing a registered pharmacist; such items may be unavailable in convenience or grocery stores that stock other non-restricted OTC medications.
For example, many U.S. drugstores have moved products containing pseudoephedrine, an OTC product, into locations where customers must ask a pharmacist for them. A prescription is not required; the change has been made in an effort to reduce methamphetamine production. Since the passage of the Methamphetamine Precursor Control Act, the purchase of pseudoephedrine in the United States is restricted. Sellers of pseudoephedrine must obtain and record the identity of the purchaser and enforce quantity restrictions. Some states may have more stringent requirements (e.g. Oregon, where a medical prescription is required to purchase any quantity of pseudoephedrine). Despite these restrictions, products containing the substance are still considered OTC in all states except Oregon, since no prescription is required.
A similar regulation applies to various forms of Emergency Contraception. The FDA considers these products to be OTC substances for women aged 17 or over, but prescription drugs for younger women.  To enforce this restriction and to provide counseling and education on proper use, an agreement between the manufacturer and the FDA requires that these drugs are stored behind the pharmacy counter. Women may obtain the medication without a prescription after providing proof of age to pharmacy staff and receiving any necessary patient education.
Furthermore, some Schedule V controlled substances may be classified as OTC products in certain states. Such drugs are sold without a prescription, but are subject to record-keeping rules, quantity and/or age restrictions, and must be dispensed by a pharmacy.
In the United Kingdom, medication will fall into one of three categories
Medication available only with a prescription is marked somewhere on the box/container with [POM]. Over-the-counter medicines are marked with [P]. A prescription is not required for [P] medicines and pharmacy sales assistants are required by RPSGB codes to ask certain questions, most of all, whether the patient is taking other medication, before selling these; in fact many pharmacies sell [P] medication "no questions asked". It is with this information that the pharmacist can halt the sale, if need be. Some medication available in supermarkets and petrol stations is sold there only in smaller packet sizes. Often, larger packs will be marked as [P] and available only from a pharmacy. Frequently, customers buying larger than usual doses of [P] medicines (such as DXM, promethazine, codeine or Gee's linctus) will be queried, due to the possibility of abuse.
As a general rule, over-the-counter drugs have to be primarily used to treat a condition that does not require the direct supervision of a doctor and must be proven to be reasonably safe and well-tolerated. OTC drugs are usually also required to have little or no abuse potential, although in some areas drugs such as codeine are available OTC (usually in strictly limited formulations or requiring paperwork or identification to be submitted during purchase). One of the oldest OTC drugs is aspirin.
Over time, often 3-5 years, drugs that prove themselves safe and appropriate as prescription medicines, may be switched from prescription to OTC. An example of this is diphenhydramine (Benadryl) which once required a prescription but now is available OTC nearly everywhere. Diphenhydramine is an anti-histamine. More recent examples are cimetidine and loratadine in the United States, and ibuprofen (Herron Blue/Nurofen) in Australia.
It is somewhat unusual for an OTC drug to be withdrawn from the market as a result of safety concerns, rather than market forces, though it does happen occasionally, phenylpropanolamine is one such example, after it was removed from sale in the United States over concern regarding strokes in young women.
In the United Kingdom, it was announced In February 2007, that Boots the Chemist would try over the counter sales of Viagra in stores in Manchester, England (previous available as prescription only). Men aged between 30 and 65 would be eligible to buy four tablets after a consultation with a pharmacist..
Over-the-counter drugs (OTC) are drugs that do not need a prescription to be bought. When they are properly used, these drugs do not put the health of the patient in danger. Many OTC drug ingredients which were prescription drugs are now considered safe enough for use without a prescription. In many countries, there are special government agencies that regulate OTC drugs, such as the Food and Drug Administration and the Drug Enforcement Administration in the United States. Certain drugs are classified as over-the counter drugs, but may only be given by a pharmacist. This is often the case with emergency contraception medicine. It may also be the case that a small packet of a certain drug is available over the counter, but that larger packets require a prescription.