What is HHC: Is it legal or prescribed in the UK?

Hexahydrocannabinol (HHC, and sometimes referred to as HXC) is one of the more recent man-made cannabinoids to arrive on UK shores, sporting huge (but totally unfounded, and in some regards extremely irresponsible) marketing claims and more than slightly blurry details.

Billed as a ‘legal’ alternative to THC, it’s turning up in vapes, edibles, and even so-called “HHC flower” and “HHC hash”, though the compound itself is semisynthetic, totally unregulated, and now banned in the UK.

It’s the sort of chemical that naturally invites a certain level of curiosity, thrives in legal ambiguity, and has earned more than a raised eyebrow from the medical world and regulators.

So…

• What is HHC?

• How is HHC made?

• What types of HHC products are available in the UK?

• What does HHC do?

• And why are some people seeking it out, while doctors and regulators firmly voice their concerns? 

Here, we explain exactly what HHC is, and why it’s not a safe substitute for legally prescribed medical cannabis.

What is HHC, and how is it different from THC and CBD?

HHC has a very similar chemical make-up to THC, but those small changes can affect how strong it feels, how long it lasts, and how your body processes it. It was first synthesised in the mid-1940s to be used as a research chemical, but popped up on the recreational market in early 2021 in vapes, edibles, and other products marketed as “legal highs”. 

While plants in the Cannabis sativa L. genus (cannabis and hemp) do produce HHC, they do so in minuscule, close to undetectable, amounts. All commercial HHC is synthesised in a lab, usually starting with CBD extracted from industrial hemp cultivars. 

That makes HHC what’s known as a “semi-synthetic cannabinoid”. It is technically derived from the plant, but a few steps (and solvents) removed from anything you’d find growing in nature. HHC products are not licensed for medical use in the UK, and they carry none of the legal or clinical safeguards that come with prescribed cannabis-based treatments.

HHC vs THC and CBD

Structurally, HHC is nearly identical to THC (and close to CBD), but with two extra hydrogen atoms. It’s a small change on paper, but enough to make the molecule a totally separate entity.

HHC comes in two main forms:

• 9R-HHC, which is psychoactive, binds to cannabinoid receptors in what is thought to be a similar way as THC
• 9S-HHC, which binds weakly and has almost zero measurable psychoactive effect

Most products on the market contain a mixture of both, though you’re rarely told how much of each. That means the same dose from two different HHC products (even the exact same products from different batches) could produce two entirely different experiences, or, none at all.

Meanwhile, clinically approved (and naturally occurring) cannabinoids like THC and CBD have been far more thoroughly studied. In the UK, both can be prescribed legally through specialist clinics like Releaf. 

The products we prescribe are not anonymous imports or unlabelled extracts. They are medical-grade treatments, typically in the form of dried flower, oil, or vape cartridges, and they’re prescribed for specific conditions or symptom alleviation. 

Every product prescribed by Releaf is manufactured in a GMP-certified facility, comes with a certificate of analysis, and is subject to strict regulatory oversight. It is the difference between clinical care and chemical guesswork, and for patients with health concerns, that distinction matters.

How is HHC made?

HHC is produced in a lab using a chemical process called hydrogenation. Manufacturers usually start with CBD extracted from hemp, then convert it into a THC-like compound, and alter its structure by adding hydrogen atoms. 

HHC isn’t something naturally taken from the plant. It’s made in a lab by changing the chemical structure of other cannabinoids (usually hemp-derived CBD) using heat, pressure, and strong solvents to force the transformation.

What does HHC do?

Right now, we only have access to anecdotal evidence. There are no published clinical trials in humans, no therapeutic guidelines, and no established medical use. What we know comes from online forums, product reviews, and self-reported experiences (none of which are reliable indicators of safety or consistency).

What do people say HHC feels like?

Most people who have tried HHC describe the effects as similar to THC, but slightly milder. That is, a sense of relaxation, a subtle body high, and sometimes drowsiness. Others report feeling very little at all. 

Much of this variability likely comes down to the ratio of HHC’s two isomers (9R, which is active, and 9S, which is not). Most products probably contain both, but in inconsistent amounts. Again, since there are no lab reports available, it’s impossible to say with full confidence what is in any given HHC product.

Add to that the fact that we all metabolise cannabinoids differently, and that genetic factors play a role in how we respond to them, and it’s no surprise that one person’s “mild buzz” might be another’s total blank.

In short, HHC products can produce intoxicating effects, but some may offer very little in terms of psychoactivity. Either way, none of it has been verified in a clinical setting, and none of it is backed by the kind of evidence required for safe prescribing.

Is HHC safe?

In all honesty, we just don’t know. 

There is no long-term safety data, no clinical guidance, and no consistent product standards. What we do have is a growing number of unregulated products, often with little to no transparency about how they’re made or what they contain.

The concern is not just what is created, but how. 

These industrial processes can leave behind trace solvents or heavy metals if not properly removed. In regulated medicine, that would trigger a batch rejection. In the unregulated HHC market, no one is checking.

There are no mandatory tests. No oversight. No clinical trials. Just chemically altered cannabinoids, produced at scale and sold without meaningful quality control. The risk does not begin with how it feels. It starts long before it reaches the shelf.

What side effects do people report with HHC?

HHC can bring on dry mouth, red eyes, drowsiness, and a slight increase in appetite. Some people also report anxiety spikes, a restless or uneasy sensation, or a bit of mental fuzziness that carries through to the next day. 

What types of HHC products are sold in the UK?

Despite being illegal under the Psychoactive Substances Act of 2016, HHC products are still being sold online and in some UK shops. These include disposable vapes, oils, gummies, tinctures, and even so-called HHC “flower” and “hash.” 

In every case, the HHC is not extracted from the plant. It is synthesised in a lab, then applied to other materials (in the case of HHC flower or hash) to mimic the appearance of natural cannabis products.

• “HHC Flower” is almost always industrial hemp flower sprayed with a lab-made HHC extract. 
• “HHC Hash”  is usually made in almost the same way as regular cannabis hash, but with one massive caveat: the trichomes are stripped from the plant material, but this is then mixed with a synthetic cannabinoid HHC extract. 

The result may look familiar, but these HHC products share little with natural cannabis, especially with prescribed medical cannabis products. 

Without accurate labelling or standardised testing, users simply have no way of knowing what they are consuming, or, how it may affect them.

Does HHC have any place in UK medical cannabis treatment plans?

No. Well, not from a clinical standpoint anyway. 

As we mentioned earlier, some medical cannabis cultivars may contain trace, almost undetectable levels of HHC, but this would not be considered to be a part of the active ingredients, and certainly not the focus of any treatment plan.

HHC is not prescribed, not clinically researched in humans, and not approved by regulatory bodies. Releaf patients do not have to worry about untested, unregulated, or potentially unsafe products. Every prescribed medical cannabis product we offer comes from GMP-certified facilities and is subject to the full breadth of strict regulatory oversight, ensuring quality, consistency, and patient safety at every stage.

All treatment plans are prescribed and monitored by our the specialists that make up our world-class clinical team, who not only have experience in prescribing both conventional and cannabis-based treatment options, but also cover a wide range of clinical backgrounds. Their expertise allows them to put together treatment plans that are evidence-based, personalised to your health needs, and grounded in safe medical practice.

HHC FAQs

Does HHC show up on a drug test?

Most drug tests screen for THC metabolites, not HHC itself. However, because HHC is structurally similar to THC, it may still trigger a positive for THC, especially on basic urine tests. 

There is no reliable data, so it's safest to assume there is some risk.

Can you build a tolerance to HHC?

There is no formal research on HHC tolerance in humans. That said, it acts on the same receptors as THC, so regular use could lead to reduced sensitivity over time. 

Until proper studies exist, the assumption is yes.

What is HHC-O, and is it legal in the UK?

HHC-O is another lab-made cannabinoid - the acetate version of HHC. Online forums and reviews show that it is often described as more potent than HHC. It is not naturally occurring and, like HHC, is considered illegal under UK law. 

It is not regulated, not prescribed, and has not been tested in clinical settings.

Final thoughts - HHC vs THC and medical cannabis

HHC is a compound full of claims, but very few actual answers, and even fewer safeguards. Where it comes from, how it’s made, and what it actually does are all still open questions. 

Despite that, HHC has found its way into shops, online stores, and social feeds, often pitched as a shortcut to something vaguely recreational, occasionally even dressed up with baseless health claims.

But there should not be any shortcuts when it comes to your health. 

HHC, when lab-made and added to unregulated products, is unpredictable and illegal in the UK. While there may be tiny traces of HHC in prescribed medical cannabis, it does not form part of any licensed treatment plan, and HHC products offer none of the care, oversight, or clinical accountability that should come with adding cannabinoids to a treatment plan.

At Releaf, we believe cannabis-based treatment should be handled with the same level of regulatory scrutiny and therapeutic expertise as any other form of healthcare. If you're considering it as part of your health journey, you deserve advice that’s grounded in evidence, guided by experience, and focused entirely on your wellbeing. 

To find out if you may be a candidate for medical cannabis treatment in the UK, head to our fast and free medical cannabis eligibility checker. It takes just 20 seconds to complete.