Oils, sprays, capsules or flower? Routes of administration explained

When people talk about medicinal cannabis they often focus on which cannabinoid — THC or CBD. But how you take a product matters just as much. The route of administration changes how quickly the medicine reaches your bloodstream, how long the effect lasts, and how predictable the dose is. Understanding the trade-offs helps you and your prescriber match the product to your needs.

The main routes at a glance

Route	Onset	Duration	Predictability
Vaporised / inhaled flower	Seconds–minutes	2–4 hours (sometimes longer)	Hardest to dose precisely
Oromucosal spray / sublingual drops	Within ~15 minutes	Several hours	Moderate
Swallowed oil / capsule	1–3 hours	6–12 hours (up to 24)	Slow, variable
Topical	Minutes to ~1 hour, local	A few hours locally	Minimal systemic effect
Transdermal patch	Slow (hours)	Many hours to over a day	Steady, slow release

Inhaled (vaporised flower)

Inhalation is the fastest route — effects appear within seconds to minutes — which makes it well suited to breakthrough symptoms that need quick relief. The trade-off is that it's the hardest to dose precisely, since how much you absorb depends heavily on technique, and the effects fade relatively quickly.

A crucial safety point: vaporise rather than smoke. Combustion (smoking) produces tar, polycyclic aromatic hydrocarbons and carbon monoxide. Vaporisers heat the plant to a lower temperature (around 180–210°C) and deliver comparable THC while suppressing those harmful byproducts. Lower vaporiser temperatures are preferable, because terpenes can degrade into irritants at high heat.

Oromucosal and sublingual

Sprays applied to the inside of the cheek (like Sativex) and drops held under the tongue are absorbed partly through the lining of the mouth, partly bypassing the liver's first-pass metabolism. They reach the bloodstream within about 15 minutes — faster than swallowing — with effects lasting several hours. This route offers a reasonable middle ground between the speed of inhalation and the duration of oral products, and it's useful for patients who can't or don't want to inhale.

Oral (oils, capsules, edibles)

Swallowed products are the slowest and most variable, with onset over one to three hours and effects lasting many hours — NZ guidance notes up to 24 hours. Two things drive the variability:

• First-pass metabolism. Swallowed THC is heavily converted by the liver into 11-hydroxy-THC, a metabolite described in the literature as roughly equipotent to THC. This is why oral THC can feel stronger and last longer than the same dose inhaled.
• Food. A high-fat meal dramatically increases absorption — in one pharmaceutical study of oral CBD, by several-fold. Taking oral products consistently with respect to food improves predictability.

The big practical risk with oral products is redosing too soon: feeling nothing after 30 minutes, taking more, and then being hit by the full combined dose hours later. Respect the onset window.

Topical and transdermal

Topicals (creams, balms) act locally with minimal systemic absorption — useful for localised issues, with little intoxication risk. Transdermal patches release slowly through the skin over many hours, giving steady levels, though absorption is low without permeation enhancers. Both are less commonly used than oral and inhaled products in NZ practice.

How prescribers choose

The choice usually flows from the symptom and the patient:

• Fast relief needed (breakthrough pain, acute nausea): inhaled or oromucosal.
• Steady, all-day or overnight coverage: oral.
• Avoiding intoxication and impairment (work, driving concerns): non-intoxicating CBD products, often oral.
• Difficulty swallowing or wanting faster onset without inhaling: oromucosal.
• Localised problem: topical.

Many patients end up using more than one route — for example a long-acting oral product for baseline symptoms plus a faster product for flare-ups.

Practical tips

• Match route to purpose, and don't expect a slow oral product to act like an inhaler.
• Respect onset times, especially for oral products, to avoid accidental overdosing.
• Be consistent with food when taking oral products.
• Prefer vaporising over smoking, at lower temperatures.
• Discuss the route with your prescriber — it's as much part of the prescription as the cannabinoid and dose.

The bottom line

There's no single "best" route — each trades speed against duration and predictability. Inhalation is fast but imprecise; oral is durable but slow and variable; oromucosal sits in between; topicals act locally. Choosing well, and using each route as intended, is a big part of getting medicinal cannabis to work for you.

Last reviewed 28 September 2026 — education, not medical advice. Sources: Lucas 2018 — pharmacokinetics; Huestis 2007; bpacnz.