PRN is an abbreviation used in medicine and sometimes found on prescriptions. This stands for ‘pro re nata’, which is a Latin phrase that in turn loosely translates to ‘as needed’, ‘occasionally’ or ‘according to circumstances’.
This will sometimes be seen in notes or instructions and essentially means that a particular treatment or medication is to be used at the nurse or GP’s discretion. For example, this might be used to describe the use of pain medication. Here, the doctor might give an order for ‘X-medication q4h PRN’ and that basically means that the pain medication is only needed if the patient asks for pain management, or if their carers deem it to be useful. However, this does not mean that the patient may use as much of the medication as they wish, rather that they may use some if needed. Maximum dosage should never be exceeded.
There is however a similar term which means a medication can be used as much as the patient wishes. This term is ‘Ad Libitum’, which is in turn shortened to ad lib – an expression you may have heard in reference to acting or music (and which has essentially the same meaning as ‘at liberty’). It is very rare to see this note in a medicinal setting, though it might be suitable for example where a placebo has been prescribed.
A lot of terms and expressions used in medicine are Latin as this is considered to be the ‘universal’ language for medicine. Abbreviations such as PRN are meanwhile very common in doctor’s notes and medicine as a useful way of saving time. Doctors have to take copious notes while treating patients and using shorthand can help to make those notes more legible while also allowing them to see more patients in a shorter amount of time.