||The examples and perspective in this article may not represent a worldwide view of the subject. (January 2013)|
Over-the-counter (OTC) drugs are medicines sold directly to a consumer without a prescription from a healthcare professional, as compared to prescription drugs, which may be sold only 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. OTC drugs are usually regulated by active pharmaceutical ingredients (APIs), not final products. By regulating APIs instead of specific drug formulations, governments allow manufacturers freedom to formulate ingredients, or combinations of ingredients, into proprietary mixtures.
The term over-the-counter may be somewhat counterintuitive, 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 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 pharmacist 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.
Regulation by country 
An intermediate category—non-prescription items that must be kept behind the counter, in a store room, or on a shelf readily visible by the pharmacist, which includes weak codeine products, muscle relaxants, and some antihistamines—exists.
United States 
In the United States, the manufacture and sale of OTC substances is regulated by the Food and Drug Administration. The FDA requires that all "new drugs" 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 would not be required to obtain an NDA and could remain on the market if they conformed to the monograph guidelines for doses, labeling, and warnings which are finalized in the Code of Federal Regulations.
Thus, in the United States an OTC drug product is allowed to be marketed either: (1) pursuant to an FDA monograph; or (2) pursuant to an NDA for products that do not fit within a specific monograph. There is also the possibility that certain OTC drug products are marketed under the grandfather provisions of the Federal Food, Drug, and Cosmetic Act, but FDA has never formally acknowledged that any legitimate grandfather OTC drug exists.
Examples of OTC substances approved in the United States 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 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.
Restricted OTC Substances 
An ill-defined third category of substances comprises 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 counter and are sold only in stores that are registered with their state. 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 Illinois Methamphetamine Precursor Control Act and the subsequent Federal Combat Methamphetamine Epidemic Act of 2005, 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). After initial attempts to control meth use by requiring documentation of sale with government issued ID as well as limits on the quantity an individual could purchase failed to realize meaningful reductions in methamphetamine use and production, Mississippi passed House Bill 512 in the State Senate on February 2, 2010," to require a prescription from a licensed medical professional to purchase over-the-counter medicines with pseudoephedrine, ephedrine, or any other precursor chemical that can readily and illicitly be converted into methamphetamine, Methcathinone or any active/scheduled analogs of Phenylethylamines/ amphetamine. Despite these restrictions, products containing the substance are still OTC in most states, 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 and quantity and/or age restrictions, and must be dispensed by a pharmacy.
United Kingdom 
- Prescription Only Medication (POM), which are legally available only with a valid prescription from a prescriber. A pharmacist has to be on the premises for POM medicines to be dispensed, required by law. The medicine has been specifically prescribed for the patient holding the prescription, so it is considered safe for only the recipient to take. Just a small example of these include most Antibiotics, and all Antidepressants or Antidiabetic medications. Drugs also included as POM are high-strength painkillers such as Oxycodone and Tramadol, medications such as Sildenafil (Viagra) and Diazepam (Valium), and certain topical preparations such as nCorticosteroids. These medicines are often sold by drug dealers, especially those marked as "CD POM," which are controlled due to abuse risk such as Diconal, Temazepam, and Methadone.
- General Sales List (GSL), available off the shelf with no pharmacy training required to sell (so they can be sold anywhere, such as supermarkets). In general, they are considered safe for most people when taken correctly. Examples of these include 16-packs (or less) of painkillers such as paracetamol & ibuprofen as well as a host of other safe medications such as small pack sizes of Antiallergy tablets, Laxative medication, and skin creams.
- Pharmacy Medicines (P), are medicines which are legally neither a POM or GSL medication. These can be sold from a registered pharmacy but should not be available for self-selection (although directions to discuss a 'P' product may also be allocated shelf space with associated GSL items). 'P' medications are reserved from the GSL list as they are either associated with a need for advice on use, or used in conditions which may require referral to a medical prescriber. Suitable trained counter assistants may sell a 'P' medication under the supervision of a pharmacist and will ask questions to determine if the customer needs to be referred for a discussion with a pharmacist. Some 'POM' medicines are available for use in certain situations and doses as 'P' medicines.
If it is not appropriate to sell a 'P' medication, i.e. the condition is not suitable for self-management and requires referral to a medical prescriber then a sale should not occur and the pharmacist has a legal and professional obligation to refer this on to an appropriate service. Examples of these include some sleep aid tablets such as Nytol, Human de-worming tablets such as Mebendazole, painkillers with small amounts of Codeine (up to 12.8 mg per tablet), and pseudoephedrine. Medication available only with a prescription is marked somewhere on the box/container with [POM]. Pharmacy-only products are marked with [P]. A prescription is not required for [P] medicines, and pharmacy sales assistants are required by Royal Pharmaceutical Society codes to ask certain questions, which varies for what the customer says. If they ask for a specific product, the Pharmacy Assistant must ask "Who is it for," "How long have you had the symptoms," "Are you allergic to any medication," "Are you taking any medication" (WHAM Questions). If a customer asks for a remedy, e.g., hay fever, then the 2WHAM questions must be followed "Who is it for," "What are the symptoms," "How long have you had the symptoms," "Have you taken any action towards your symptoms," and "Are you taking any other medication." It is with this information that the pharmacist can halt the sale, if need be. No [POM] [P] or [GSL] products that are stocked in a pharmacy can be sold, dispensed, or pre-made until a responsible pharmacist is signed in and on the premises. Some medication available in supermarkets and petrol stations is sold 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. 
Switches between prescription and OTC 
As a general rule, over-the-counter drugs have to be used primarily 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 3–6 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. A study has been done examining consumer's perceptions about the risk of and access to nonprescription medication. A substantial minority of the public appears willing to accept considerable risk to gain greater access to pharmaceuticals.
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.
See also 
- Child-resistant packaging
- Generic drug
- Generally recognized as safe and effective
- Inverse benefit law
- List of drug interactions
- Medical prescription
- Regulation of therapeutic goods
- Over-the-Counter Medicines: What's Right for You?. Fda.gov (2009-04-30). Retrieved on 2012-07-04.
- The New Over-the-Counter Medicine Label: Take a Look. Fda.gov (2012-04-27). Retrieved on 2012-07-04.
- FDA Approves Plan B One-Step Emergency Contraceptive; Lowers Age for Obtaining Two-Dose Plan B Emergency Contraceptive without a Prescription. Fda.gov. Retrieved on 2012-07-04.
- FDA Approves Over-the-Counter Access for Plan B for Women 18 and Older. Fda.gov (2009-04-30). Retrieved on 2012-07-04.
- Availability of medicines. MHRA. Retrieved on 2012-07-04.
- Alexander, GC; Mohajir N, Meltzer DO (2005). "Consumers' perceptions about risk of and access to nonprescription medications". Journal of the American Pharmacists Association 45 (3): 363–370. doi:10.1331/1544345054003868. PMID 15991758.
- "Over-the-counter Viagra piloted". BBC News. 2007-02-11. Retrieved 2009-02-10.
-  FREE software to better understand OTC drug and drug interaction. Consumer can freely download software in smart phone or use web widget to check drug-drug interaction.;
-  The Tan Sheet is the weekly source of OTC industry news in the US;
-  OTC Product News comments on news and events effecting the OTC industry;
- Over-the-counter (OTC) Medicines at FamilyDoctor.org, maintained by the American Academy of Family Physicians. Contains extensive information on over-the counter drugs and their responsible use, including specific guidance on several drug classes in question-and-answer format and information on common drug interactions.