The written direction for drugs for medicinal use, given by the doctor, dentist and (for some drugs) nurse to the patient, for dispensing by a pharmacist. Drugs should only be prescribed when essential for treatment, and when any possible risks involved to the patient (and fetus in cases of pregnancy) are outweighed by the potential benefits of giving the drug and when the recipient has been fully informed and consents. When possible, non-proprietary, or generic, titles are prescribed; by allowing the pharmacist to dispense any equivalent drug this avoids delay for the patient, as well as reducing the cost. Dosage is generally stated in metric units, and both the amount and frequency should be carefully explained to the patient by the doctor, and clearly written when the drug is dispensed (see also DOSAGE; DRUGS). Strict adherence to legislation is necessary to restrict the inappropriate prescription and abuse of drugs. Full details of drugs available on NHS prescription are given in the British National Formulary (BNF), which is distributed to all NHS doctors by the government. (See also PROPRIETARY NAME and GENERIC DRUG.)