The way a cannabis medicine enters the body changes how much reaches the blood, how fast it acts and how long it lasts. Inhaled cannabis acts within 5–10 minutes and lasts 2–4 hours. A swallowed dose can take 30 minutes to 3 hours to act, and only 4–20 per cent of it reaches the blood. This part covers products held under the tongue, creams, suppositories, the dosage forms a prescriber may choose, standardised products and special patient groups. It ends with the Thai rules.
Translator’s note: Relatives and patients often ask growers in Thailand how medical cannabis “should be taken”. This article does not replace a prescriber. It explains the evidence so that you can bring better questions to a licensed practitioner.
This is Part 2. Part 1: Routes of Administration for Medical Cannabis: Why How You Take It Changes Everything
Under the tongue and mouth sprays
A sublingual product is held under the tongue. An oromucosal product is absorbed through the lining of the mouth. The best-studied example is nabiximols, a licensed mouth spray made from a standardised plant extract. Each 100-microlitre spray contains 2.7 milligrams of tetrahydrocannabinol (THC, the main intoxicating cannabinoid) and 2.5 milligrams of cannabidiol (CBD).
Its Summary of Product Characteristics is the official document that describes an approved medicine in Europe and the UK. According to this document:
- cannabinoids appear in the blood within about 15 minutes
- the peak level comes at 45–120 minutes
- blood levels are lower than after inhaling
- the coefficients of variation are 57.3 and 64.1 per cent. This means the spread of results between people was more than half of the average value, which is very large.
Translator’s note: Ask your prescriber whether nabiximols is available in Thailand.
Why much of it is swallowed anyway
The lining under the tongue drains straight into the general bloodstream, so that part of the dose skips the liver. However, much of any product placed under the tongue is swallowed.
Erin Karschner and colleagues tested this in nine participants. The results were published in Clinical Chemistry in 2011. They compared a measured swallowed dose of THC with the mouth-spray extract. They found no statistically significant differences in peak level, time to peak or total exposure. The relative bioavailability of the swallowed form was 92.6 and 98.8 per cent. In other words, swallowing delivered almost as much as the spray.
Lesson: some of the dose really is absorbed under the tongue, which is why onset is earlier. But holding an oil under the tongue does not stop the swallowed part from passing through the liver first.
What to do: treat an oil held under the tongue as a partly swallowed product. Use the same waiting time before any extra dose, and the same meal routine, that you would use for a swallowed oil.
Creams and balms: local, not whole-body
A topical product acts where you put it. A transdermal product is designed to pass through the skin into the blood.
A 2022 review in Pharmaceutics explains why the two are different. It uses log P, a scale of how strongly a substance prefers fat over water. Cannabinoids score about 6–7. Drugs that cross intact skin in approved skin patches score 1–3. Cannabinoids are too fat-loving to pass easily through the skin into the blood.
A cream or balm therefore acts locally. It produces no meaningful blood levels and no intoxication. To deliver a cannabinoid into the blood through the skin, a product needs special design. Examples are permeation enhancers (ingredients that help a drug pass through the skin) and patch systems.
What to do: use a cream only for a local problem, such as one painful area. Do not expect it to treat a whole-body symptom. If a whole-body effect is needed, ask the prescriber about other routes.
Rectal suppositories: a widely repeated claim that is wrong
Many sources claim that suppositories deliver 50–80 per cent bioavailability because they bypass the liver. Do not repeat this claim. It misreads a small number of studies.
Where the claim came from
The claim traces back to Mahmoud ElSohly and colleagues at the University of Mississippi (USA). In 1991 they published a study in the Journal of Pharmaceutical Sciences using cynomolgus monkeys. They measured how much THC reached the blood from suppositories. The result was 13.5 per cent, far below the popular figure.
That 13.5 per cent applied only to THC hemisuccinate. This is a prodrug: a modified form of a drug that the body converts into the active drug. The added chemical group makes it partly water-soluble, so it can cross the lining of the rectum.
The same paper reported that swallowed THC gave low and erratic absorption. It also reported that “the drug showed no bioavailability from various suppository formulations”. Ordinary, unmodified THC in a fatty suppository base was not absorbed.
The later human study
A later human study from the same research programme was published in Medical Cannabis and Cannabinoids in 2018. In the part that compared it with a swallowed capsule, twelve volunteers took part. The hemisuccinate suppository gave 2.44 times the exposure of a swallowed capsule. The 90 per cent confidence interval was 1.78 to 3.35, meaning the true value very likely lies in that range.
This figure compares the suppository with a swallowed capsule. It does not show what share of the dose reached the blood. It also applies to a patented prodrug, not to ordinary cannabis oil.
What to do: do not make cannabis-oil suppositories at home in the hope of high absorption. No study shows that this works. If vomiting or swallowing problems make another route necessary, ask a prescriber.
Dosage forms a prescriber may choose
| Form | Usual route | What it offers | What makes it harder |
|---|---|---|---|
| Dried flower | Inhaling | Fast onset; a wide range of plant compounds | Content varies from batch to batch |
| Oil or tincture | Swallowed or under the tongue | Content stated per millilitre; quick to measure | Food changes absorption; alcohol-based tinctures do not suit some patients |
| Capsule | Swallowed | The most repeatable single unit | Slowest onset; cannot be split into smaller doses |
| Standardised extract | Swallowed, under the tongue, mouth spray | Defined, consistent content | Fewer products available; costs more |
Why standardisation matters to a patient
A standardised product has its cannabinoid content measured, stated on the label and kept the same from batch to batch. Without standardisation, a patient may settle on a dose with the prescriber and then lose that stability whenever a new batch arrives.
A 2025 study in Scientific Reports checked labelled THC content in Colorado (USA). Of 178 flower products, 43.3 per cent were more than 15 per cent away from the label. Most of the inaccurate labels overstated the THC content.
What to do: when a new batch arrives, ask for its certificate of analysis, the lab report for that batch. Compare the THC and CBD per gram or per millilitre with the previous batch. If the content has changed, your prescriber can adjust the dose before the effect changes unexpectedly.
Titration and route
Titration means changing a dose step by step until you reach the smallest amount that works. The prescriber should lead this process. The route changes what each step delivers:
- Inhaled: perhaps 8–24 per cent reaches the blood within minutes, mostly as THC itself.
- Swallowed: perhaps 4–20 per cent arrives over hours, with far more 11-hydroxy-THC. This active breakdown product is made in the liver.
- Held under the tongue: some arrives earlier. The rest behaves like the swallowed portion.
What to do: change only one thing at a time, whether that is the dose, the route or the timing around meals. Keep a written log of time taken, onset and duration. The log shows your prescriber which change caused which effect.
Special patient groups and route choice
Nausea, vomiting and difficulty swallowing
A patient who is vomiting cannot reliably keep a swallowed dose down. Nobody can then know how much was absorbed. Routes that do not depend on swallowing exist for these situations. The prescriber chooses among them, based on what is legally available.
Patients who have difficulty swallowing cannot use capsules. Liquids and mouth sprays are the usual alternatives.
Children, older patients and existing lung disease
For children, the cannabinoid medicine with the strongest regulatory approval is an oral solution, meaning a liquid that is swallowed. It can be measured precisely by body weight, and it is used where inhaling is not appropriate.
Older patients are among the patient groups that need extra care. Several factors argue for routes with modest, predictable peaks:
- changes in how the liver processes drugs
- greater sensitivity of the heart and circulation
- use of several medicines at the same time
- interactions with other medicines through cytochrome P450 (CYP), the family of liver enzymes that also breaks down THC
Some patients have asthma, chronic obstructive pulmonary disease (a long-term lung disease that makes breathing difficult) or an active chest infection. For them, inhaling needs the strongest reason of any route.
What to do: bring a full list of all your medicines and supplements to the prescriber. This is how the prescriber checks for liver-enzyme interactions before choosing a route and dose.
The Thai rules
Cannabis flower (ช่อดอกกัญชา) is a controlled herb under the Notification of the Ministry of Public Health Re: Controlled Herbs (Cannabis), B.E. 2568. This notification was issued under the Thai Traditional Medicine Protection Act B.E. 2542 and has been in force since 26 June 2025. Flower may be sold only with a PT 33 (ภ.ท.33) prescription, which covers at most 30 days. Advertising and online sale of flower are prohibited.
Tilleke & Gibbins, a Thai law firm, adds two points in its analysis. A prescription can be used only once and cannot be refilled. Seven categories of practitioner may prescribe, ranging from modern and Thai traditional medicine to pharmacy and dentistry.
What Thai patients were actually given
A nationwide study looked at what Thai patients received. It was published in Medical Cannabis and Cannabinoids in 2024 and followed 21,284 participants at 30 hospitals between September 2019 and October 2020. The main preparation was a cannabis extract in 10 per cent coconut oil. It contained 1.701 milligrams of THC per millilitre and almost no CBD. About 93 per cent of participants received it as oral drops.
The study took place before the 2025 rules, but the main point still holds. In Thailand, the most common form is an oil taken as drops, not inhaled flower. So the issues with swallowed products from Part 1 apply to most Thai patients: late onset, the effect of food and the liver’s first pass.
Smoking where others breathe the smoke
A Ministry of Public Health notification was published in the Royal Gazette on 14 June 2022 and took effect on 15 June 2022. It was issued under Section 25(5) of the Public Health Act B.E. 2535. It declared cannabis or hemp smoke or smell that may harm other people’s health a public nuisance. Failing to stop a nuisance after an official order carries up to three months in prison, a fine of up to 25,000 baht, or both.
A prescription allows a person to use a medicine. It does not allow them to smoke it where other people have to breathe the smoke.
What to do: if your prescriber approves inhaling, do it in private, away from neighbours and family members who do not use cannabis.
Translator’s note: Several rules matter if relatives or patients ask a grower for oil.
- Since 26 April 2026, the Ministerial Regulation on Cannabis or Hemp Extracts B.E. 2569 has been in force. Licences for extracts above 0.2 per cent THC are granted only to Thai juristic persons that are not “foreign” under the Foreign Business Act B.E. 2542, to state agencies and to the Thai Red Cross Society. See our topic on the two B.E. 2569 regulations.
- Processing or selling a controlled herb without a licence breaks Section 46 of the 1999 Act. Under Section 78, the penalty is up to 1 year in prison, a fine of up to 20,000 baht, or both.
- Oil made at home from your own flower has an unknown THC content per millilitre. Even with good intentions, nobody can dose it in a standardised way.
What to do: if someone asks you for oil, refer them to a licensed practitioner who can issue a PT 33 prescription. Also point them to licensed products that come with a lab certificate.
What the evidence still cannot tell us
There are three gaps:
- no long-term human data on health outcomes from vaporising dried flower
- no reliable absorption data for the under-the-tongue route that separates it from the swallowed portion
- no absorption data at all for ordinary rectal cannabis preparations
None of this makes the choice of route random. It means the choice is a clinical judgement. It should be made with a licensed practitioner who knows the patient and the law.
What to do: bring your written log of dose times, onset and duration to that appointment. It gives the practitioner your own data instead of averages.
Share your experience
Tell us below this topic which route you started on. Did anyone explain the onset time before your first dose? What changed when you switched forms? Were tested, standardised products available where you live? We would like to hear from members in Thailand and across the region. Keep to general information and leave clinical decisions to your prescriber.
References
- Nabiximols oromucosal spray. Summary of Product Characteristics.
- Karschner EL and colleagues. Swallowed THC versus oromucosal cannabis extract. Clinical Chemistry, 2011.
- Review of skin delivery of cannabinoids. Pharmaceutics, 2022.
- ElSohly MA and colleagues, University of Mississippi. Rectal bioavailability of delta-9-THC from the hemisuccinate ester in cynomolgus monkeys. Journal of Pharmaceutical Sciences, 1991.
- Human study of the THC hemisuccinate suppository versus a swallowed capsule (twelve volunteers). Medical Cannabis and Cannabinoids, 2018.
- Labelled versus measured THC content in Colorado flower products. Scientific Reports, 2025.
- Canadian Pharmacists Association and Health Canada: material on onset and duration of effect.
- Tilleke & Gibbins. Analysis of the Thai controlled-herb rules for cannabis.
- Nationwide Thai cohort of 21,284 participants, September 2019 to October 2020. Medical Cannabis and Cannabinoids, 2024.
- Notification of the Ministry of Public Health Re: Controlled Herbs (Cannabis), B.E. 2568; Thai Traditional Medicine Protection Act B.E. 2542.
- Ministerial Regulation on Cannabis or Hemp Extracts B.E. 2569.
- Ministry of Public Health notification under Section 25(5) of the Public Health Act B.E. 2535, Royal Gazette, 14 June 2022.
This article is part of the Asiannabis Community educational series on medical cannabis. It is general information, not medical advice. Decisions about treatment belong with a licensed practitioner. The content is for education within jurisdictions where medical cannabis is legally permitted.