What forms do cannabis-based medicines come in?
How a medicine enters the body changes how quickly it works, how long it lasts and how predictable it is. In this field the differences between routes are unusually large, and they are one of the main things a specialist balances.
The short answer
- Inhaled routes act within minutes and wear off within a few hours.
- Swallowed preparations act slowly, over one to three hours, and last longer.
- Slow onset causes most accidental overexposure, because people take more before the first dose has worked.
- Smoking is not used in UK medical practice. Combustion produces harmful by-products.
- The route is a clinical decision, made with the specialist, not a preference to be ordered.
The main routes and how they differ
Three routes account for nearly all UK practice: inhalation by vaporiser, oral preparations that are swallowed, and preparations absorbed under the tongue or inside the cheek.
| Route | Onset | Duration | Main considerations |
|---|---|---|---|
| Inhaled (vaporised) | Minutes | Two to four hours | Fast, easier to titrate by feel; requires a device and technique; shorter cover overnight |
| Oral (swallowed) | One to three hours | Six to eight hours or more | Slow and variable onset; affected by food; the route where overexposure most often happens |
| Under the tongue / inside the cheek | Fifteen to forty-five minutes | Intermediate | Avoids first-pass metabolism; taste and technique matter; often used where steady cover is wanted |
Many patients end up using more than one route — something longer-acting as a background, and something faster for breakthrough symptoms. That is a clinical decision made with the prescriber.
Why slow onset causes problems
The commonest cause of an unpleasant experience with a swallowed preparation is taking a second dose because the first did not seem to be working.
Oral absorption is slow and variable. It depends on whether you have eaten, on what you have eaten, and on individual differences in metabolism. An hour can pass with nothing apparently happening, and then both doses arrive together.
The rule that prevents this is simple and worth following literally: wait the full time your prescriber specifies before considering whether anything is needed, every time, including on days when it seems to be taking longer than usual.
Why smoking is not part of UK medical practice
Burning plant material produces tar, carbon monoxide and a range of combustion by-products that are irritant and carcinogenic. None of that has any therapeutic purpose.
Where an inhaled route is clinically appropriate, vaporisation is used instead: the material is heated to release the active compounds without combustion. The comparison is set out in Vaporising versus smoking.
Mixing with tobacco — still common in the UK — adds nicotine dependence and the full range of smoking-related harms on top. A prescriber will ask about this directly, and it is worth answering honestly.
How the route gets chosen
It follows from the clinical problem. Symptoms that come in episodes point one way; symptoms that are constant point another.
- Constant background symptoms — a longer-acting route usually makes more sense
- Episodic or breakthrough symptoms — a faster-acting route may suit better
- Night-time symptoms — duration matters more than speed of onset
- Respiratory disease — an inhaled route may be unsuitable
- Swallowing difficulties, nausea, or gut conditions — affect what is absorbed reliably
- Work, driving and daily commitments — duration of any impairment matters
We do not name, compare or price products anywhere on this site. UK medicines advertising law does not permit it, and that constraint is explained in Is medical cannabis legal in the UK?
Frequently asked questions
What forms does medical cannabis come in?
In UK practice, mainly preparations that are inhaled using a vaporiser, preparations that are swallowed, and preparations absorbed under the tongue or inside the cheek. The route is a clinical decision made with the prescribing specialist.
Which works fastest?
Inhaled routes act within minutes and last two to four hours. Preparations absorbed under the tongue take fifteen to forty-five minutes. Swallowed preparations take one to three hours but last considerably longer.
Why is smoking not used?
Combustion produces tar, carbon monoxide and other harmful by-products with no therapeutic purpose. Where inhalation is clinically appropriate, vaporisation is used instead.
Why did nothing happen for an hour and then a lot at once?
That is characteristic of swallowed preparations, where absorption is slow and variable. It is also why taking a second dose early is the commonest cause of an unpleasant experience. Wait the full time your prescriber specifies.
Sources and further reading
Every factual statement on this page is drawn from the following public sources. Links open in a new tab and are not affiliated with Flora House.
- British National Formulary: Cannabis extracts
- NICE guideline NG144: Cannabis-based medicinal products
- National Academies of Sciences, Engineering, and Medicine. The Health Effects of Cannabis and Cannabinoids: The Current State of Evidence and Recommendations for Research (2017)
- NHS: Medical cannabis (and cannabis oils)
- MHRA: The supply, manufacture, importation and distribution of unlicensed cannabis-based products for medicinal use