Cannabinoids stimulate appetite. Everyone knows it, and the mechanism is well described. Dronabinol, a synthetic THC, also carries a US appetite indication: it was added in 1992 for AIDS-related anorexia, seven years after the drug was first approved for chemotherapy nausea. Then came the trials in cancer patients. Cannabis extract, THC and placebo showed no meaningful difference. When dronabinol was tested directly against an older drug, it lost on both appetite and weight. This is the gap between a real pharmacological effect and a useful clinical treatment.
Nothing here is medical advice or a reason to change anything. Appetite loss and weight loss in serious illness are managed by the treating team, and unexplained weight loss always needs medical assessment rather than a remedy. In Thailand cannabis flower is a controlled herb dispensed only on prescription form PT 33 by an authorised practitioner.
1. Two Different Problems With One Symptom
The most important distinction in this subject is one that non-clinical sources routinely collapse.
Anorexia means loss of appetite. The person does not want to eat. Fix the appetite and, in principle, they eat.
Cachexia is something else: a metabolic wasting syndrome driven by inflammation, in which the body breaks down muscle and fat regardless of intake. It is not simply not-eating, and — this is the part that matters — it cannot be reversed by calories alone. A patient with established cancer cachexia who eats more does not thereby regain the muscle.
The two overlap in real patients, and appetite stimulation addresses one of them. That single fact explains most of what follows: an appetite-stimulating drug can work exactly as designed and still fail to treat cachexia, because appetite was never the limiting factor.
2. The Mechanism, Which Is Real
The body’s own endocannabinoids act on the same CB1 receptors as plant THC and are an established part of appetite regulation; they have even been detected in milk, where researchers have proposed they help drive an infant’s feeding. That mechanism is well founded, and nothing in this article disputes it.
3. The “Dual Effect” Claim, Examined
A claim that circulates widely: cannabis reduces weight in overweight people while increasing it in underweight people — a dual action no other drug can perform.
The evidence offered is real but is being asked to carry more than it can. A study in the American Journal of Epidemiology analysed more than 52,000 participants across two US national surveys and found obesity prevalence of 22% among non-users versus 14% among users in the first survey, and 25% versus 17% in the second, with the association persisting after adjustment for tobacco, health, age and sex.
There are three problems with that evidence. It is cross-sectional epidemiology — a snapshot association, not a demonstration that cannabis changed anyone’s weight. The direction of causation is unestablished, and plausible alternatives abound, including differences in age, activity, and who uses cannabis in the first place. And the researchers themselves described the association as unexplained.
So: a genuine and repeatedly observed association, and not a demonstrated dual pharmacological action. “No other drug can do both” is a rhetorical flourish attached to a correlation.
4. What the Regulators Approved, and For What
Dronabinol is synthetic delta-9-THC in an oral capsule. The FDA approved it in 1985 for one indication: chemotherapy-induced nausea and vomiting (CINV) in patients who had not responded to conventional antiemetics. Nabilone, the other early cannabinoid drug, was approved in the US in December 1985, also for CINV. Neither original approval was for appetite.
The appetite indication came later: in 1992 the FDA added anorexia associated with weight loss in patients with AIDS to dronabinol’s label.
Note what is on that list and what is not. Cancer-associated cachexia is not an approved indication. The appetite indication is the AIDS one. It was established in the era before effective antiretroviral therapy, when AIDS wasting was a common and often terminal presentation.
5. What the Cancer Trials Found
The Cannabis-In-Cachexia-Study-Group phase III trial (Strasser and colleagues, J Clin Oncol 2006;24:3394-3400) was a multicentre, randomised, double-blind, placebo-controlled trial in patients with advanced cancer. It had three arms, each taken orally twice daily for 6 weeks: cannabis extract standardised to 2.5 mg THC plus 1 mg CBD (n=95), THC alone at 2.5 mg (n=100), or placebo (n=48).
Result: no meaningful separation. Increased appetite was reported by 73% of patients on cannabis extract, 58% on THC and 69% on placebo. There were no significant differences between the arms in appetite, quality of life or cannabinoid-related toxicity. An independent data review board recommended stopping recruitment early because the differences between arms were too small.
Jatoi and colleagues, J Clin Oncol 2002;20:567-573, enrolled 469 evaluable patients with advanced cancer, anorexia and weight loss. They were randomised to megestrol acetate 800 mg/day (n=159), dronabinol 2.5 mg twice daily (n=152), or both (n=158).
| Outcome | Megestrol | Dronabinol | Combination |
|---|---|---|---|
| Appetite improvement | 75% | 49% (p = 0.0001) | 66% (n.s. vs megestrol) |
| Weight gain ≥10% of baseline | 11% | 3% (p = 0.02) | 8% (n.s. vs megestrol) |
Megestrol acetate, a drug from the 1980s, significantly outperformed dronabinol on both outcomes. Adding dronabinol to megestrol gave no additional benefit.
6. The Verdicts
NASEM (2017). The US National Academies of Sciences, Engineering and Medicine reviewed the evidence available up to 2017 and reached two different conclusions for the two populations:
- HIV/AIDS: limited evidence that cannabis and oral cannabinoids are effective in increasing appetite and decreasing weight loss.
- Cancer-associated anorexia-cachexia syndrome: insufficient evidence to support or refute the conclusion that cannabinoids are an effective treatment.
ASCO (2020). The American Society of Clinical Oncology’s cancer cachexia guideline (Roeland and colleagues, J Clin Oncol 2020) reached a similar conclusion from a later evidence base. Progesterone analogues and corticosteroids were the only drugs it linked to gains in appetite or weight, and clinicians may offer a short-term trial of either. For other agents, cannabinoids included, it found either no benefit or too little evidence to recommend them. It concluded that no drug can be recommended as the standard of care. A 2023 update added low-dose olanzapine as an option. Neither version endorses cannabinoids.
An Asian example. In January 2021, Japan approved anamorelin (Adlumiz), a ghrelin-receptor agonist. It is licensed for cancer cachexia in non-small cell lung, gastric, pancreatic and colorectal cancer. Ono described it as the first drug approved in Japan for this condition. It is not a cure. The approval rested mainly on Japanese studies, and it was not recognised in every other jurisdiction. Still, it shows where cachexia drug development has moved: towards agents designed for the condition rather than towards cannabinoids.
Read together, these verdicts are the honest summary of this indication, and they are almost the inverse of how it is usually described. The appetite reputation rests on a 1992 approval for AIDS wasting. That approval covered a different population, in a different treatment era, at a level of evidence the reviewers grade as limited.
For what cannabinoids do and do not do in oncology more broadly, see the forum topic on cannabis and cancer (topic 1308).
7. Why the Effect Is Real and the Treatment Still Fails
Three explanations fit the pattern, and they are not mutually exclusive.
The dose in the trials was small. Dronabinol at 2.5 mg twice daily is a modest dose, chosen to limit psychoactive effects in frail patients. Frail, elderly, often cognitively vulnerable cancer patients are precisely the group least able to tolerate more. The dose that works and the dose that is tolerable may not overlap.
Appetite was not the bottleneck. In established cachexia, the inflammatory catabolic process continues regardless of intake. Stimulating appetite in that setting is treating the wrong variable.
The competitors are not weak. Megestrol was not a placebo. Dronabinol lost to an active comparator with a track record. That is not the same as saying megestrol is the answer, as the next section shows.
8. Megestrol Is Not the Easy Answer Either
Megestrol’s advantage over dronabinol in appetite and weight is real but modest, and it comes at a cost. The Cochrane review of megestrol for anorexia-cachexia (Ruiz Garcia and colleagues, 2013) found that it improves appetite and produces a small weight gain. It did not improve quality of life. Oedema, thromboembolic events (blood clots) and deaths were more frequent in patients taking it. Megestrol can also suppress the adrenal glands. Studies suggest the weight gained is mainly fat and fluid rather than muscle, which is exactly the tissue cachexia destroys. This is why guidelines such as ASCO 2020 limit it to a short-term trial, weighed against each patient’s clot risk, and do not present it as a long-term solution.
9. What Actually Helps
Appetite loss in serious illness is frequently caused by something addressable, and the first move is to look rather than to prescribe an appetite stimulant. Common reversible contributors: mouth pain, oral thrush, poorly controlled nausea, constipation, uncontrolled pain, depression, medication side effects, and taste changes from chemotherapy. Each has a specific treatment, and each is more likely to help than an appetite stimulant layered on top.
Beyond that, three things help: dietetic input; treating nausea properly, which is the one area here where cannabinoids do have a guideline position as a later-line option for chemotherapy nausea; and early involvement of palliative care, which improves symptom burden and quality of life in advanced cancer.
And one point that is not clinical but matters more than most of the above. In advanced disease, weight is often the wrong goal. Families frequently experience a patient’s not eating as the illness winning, and pressure around food becomes a source of distress for everyone. Where cachexia is established and irreversible, the achievable aim is usually that eating stays comfortable and pleasurable, not that the number on the scale moves. Clinicians who say this out loud early spare families a great deal.
10. In Thailand
Cannabis flower is a controlled herb under the Notification of the Ministry of Public Health Re: Controlled Herbs (Cannabis) B.E. 2568, issued 26 June 2025. Flower may be dispensed only against a prescription on form PT 33 from an authorised practitioner. Each prescription covers no more than 30 days and is single use (no refills), and sold flower must come from a GACP-certified cultivation site. Online sale or advertising of flower is not permitted, and recreational use is not allowed.
Two Ministerial Regulations B.E. 2569 tightened licensing in 2026: one on cannabis/hemp extracts (in force 26 April 2026) and one on controlled-herb licences (in force 30 April 2026). They do not change the PT 33 prescription rules. The Cannabis Control Act is still a draft: the Cabinet approved it on 22 September 2026 and sent it to the House. (Checked as of October 2026.) For the PT 33 process in detail and later updates, see the forum topic on medical cannabis and PT 33 (topic 1358).
Whether dronabinol, megestrol or anamorelin is registered and available in Thailand is a separate regulatory question. Check it with the treating team rather than assuming.
If you are caring for someone with advanced illness who has stopped eating: what did the team check before reaching for anything — the mouth, the nausea, the bowels, the mood? That checklist is the part of this subject most likely to actually change an outcome, and the part least often described.
This article is general educational information, not medical advice. Unexplained weight loss requires medical assessment.