PRN - As Required
PRN stands for pro re nata, meaning "as required" or "as needed." When PRN appears on a medical cannabis prescription, it instructs patients to take their medication only when symptoms arise, within daily limits set by their prescribing specialist.
Key Takeaways
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PRN stands for pro re nata, a Latin phrase meaning "as required" or "as needed"
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PRN dosing allows patients to take medical cannabis only when symptoms arise, rather than on a fixed schedule
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A maximum daily dose is always specified alongside PRN instructions to ensure safe use
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PRN is one of the most common dosing abbreviations used in UK medical cannabis prescriptions
What Is PRN?
PRN is a medical abbreviation for the Latin phrase pro re nata, meaning "as required" or "as needed." When PRN appears on a medical cannabis prescription, it instructs the patient to take their medication only when symptoms arise, rather than at fixed scheduled times.
What Does PRN Mean on a Prescription?
PRN is one of the most common dosing instructions used across all areas of medicine, including medical cannabis prescriptions in the UK. According to the British National Formulary (BNF), PRN dosing allows patients flexibility to manage symptoms as they occur, within the limits set by the prescribing doctor.
For example, a prescription might read: "Inhale 0.1g–0.2g PRN, maximum 3 times daily." This means the patient should take their medical cannabis only when they experience symptoms — such as a pain flare-up or acute anxiety — up to a maximum of three doses per day.
How Does PRN Dosing Work for Medical Cannabis?
PRN dosing is particularly common for medical cannabis prescriptions because many conditions involve intermittent symptoms. A patient prescribed cannabis for chronic pain, for instance, may have days with minimal discomfort and others where symptoms are severe.
With PRN dosing, patients can:
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Take medication only when needed, reducing overall consumption
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Maintain greater control over their treatment
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Avoid unnecessary doses on days when symptoms are manageable
Your prescribing doctor will always specify a maximum daily dose alongside any PRN instruction, ensuring safe use. It is important never to exceed this maximum, even when symptoms are particularly difficult to manage.
What Is the Difference Between PRN and Scheduled Dosing?
PRN differs from scheduled dosing abbreviations like BD (twice daily) or TDS (three times daily). Scheduled doses are taken at regular intervals regardless of symptoms, while PRN gives the patient discretion over when to dose.
Some patients may have a combination — for example, a scheduled background dose with an additional PRN allowance for breakthrough symptoms. Your specialist will determine the approach that best suits your needs. Use our medical cannabis eligibility checker to see if you qualify for a consultation.
Dosing Frequency Comparison
|
Abbreviation |
Meaning |
Doses Per Day |
Schedule Type |
|
PRN |
As required |
Varies |
Patient-directed |
|
OD |
Once daily |
1 |
Fixed |
|
BD |
Twice daily |
2 |
Fixed |
|
Three times daily |
3 |
Fixed |
|
|
QDS |
Four times daily |
4 |
Fixed |
Is PRN Dosing Right for You?
The decision between PRN and scheduled dosing depends on your condition, symptom patterns, and treatment goals. PRN may be particularly suitable for patients with anxiety who experience intermittent episodes or those managing chronic pain with variable severity.
At Releaf, the UK's largest medical cannabis clinic with over 200,000 patients and 55+ specialist doctors on the GMC Specialist Register, your dosing regimen is tailored to your individual needs. If you're exploring medical cannabis treatment, check your eligibility with our medical cannabis eligibility checker — appointments are available this week.
Frequently Asked Questions
Q: What does PRN mean on a medical cannabis prescription?
A: PRN stands for pro re nata, meaning "as required." It instructs you to take your medication only when symptoms arise, up to the maximum daily dose specified by your doctor.
Q: Can I take PRN medication every day?
A: Yes, you can take PRN medication on any day you experience symptoms, provided you do not exceed the maximum daily dose stated on your prescription. Some days you may not need it at all.
Q: What is the difference between PRN and STAT?
A: PRN means "as required" on an ongoing basis — you can dose whenever symptoms arise. STAT means "immediately" and refers to a single, one-off dose to be taken right away.
Q: How do I know if PRN dosing is right for me?
A: Your specialist will recommend PRN dosing if your symptoms are intermittent rather than constant. If you need consistent relief throughout the day, scheduled dosing such as BD (twice daily) or TDS (three times daily) may be more appropriate.
Related Glossary Terms
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TDS (Three Times Daily) — take medication three times per day at regular intervals
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BD / BID (Twice Daily) — take medication two times per day, approximately 12 hours apart
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OD (Once Daily) — take medication once per day at a consistent time