What Is THC and How Does It Affect You?

In June 2012, police arrested a Cape Town attorney named Gareth Prince and his family at their home for growing cannabis. It wasn't his first run in with the law over it, and it wouldn't be his last fight either. It took another six years, but that arrest eventually led to the Constitutional Court ruling that changed cannabis law in South Africa for good. We'll come back to how his story ends. First, what actually is the compound this whole fight was about.

What THC Actually Is

THC, short for delta-9-tetrahydrocannabinol, is the main psychoactive compound in cannabis, the one responsible for getting you high. It's concentrated in the resin (trichomes) coating the flowers, and when people describe a product as strong or weak, they're usually talking, at least partly, about its THC content.

THC is chemically close to CBD, but the two behave completely differently in the body because of how each one interacts with the brain's receptor systems.

How THC Produces a High

Your body runs an internal signalling network called the endocannabinoid system, built around receptors called CB1, concentrated in the brain and central nervous system, and CB2, concentrated mainly in immune tissue. Normally this system responds to cannabinoids your own body produces, helping regulate mood, appetite, pain, memory and more.

THC closely mimics one of those natural compounds and binds hard onto CB1, far more directly than CBD ever does. That activates brain regions tied to reward, mood, memory and coordination, which is the whole mechanism behind the classic cannabis high, and also why THC can mess with short term memory and coordination while it's active.

Full explanation of the receptor system in [The Endocannabinoid System Explained].

The Effects of THC

On the upside, people commonly report euphoria or a general lift in mood, physical and mental relaxation, sharper or more intense sensory perception (colours, sounds, flavours), increased appetite, and a shifted sense of time.

On the downside, especially at higher doses or for anyone new to it, common effects include anxiety or paranoia, a faster heartbeat, dry mouth and red eyes, short term dips in memory and coordination, and dizziness.

Which way it leans depends on dose, your own tolerance and body chemistry, the product's full cannabinoid and terpene mix (see [Indica vs Sativa vs Hybrid: What the Science Actually Says] for why the indica or sativa label won't tell you this), and even your mood going in.

How Long It Lasts, and Why the Method Matters

This is probably the single most practically useful thing to understand about THC.

Smoked or vaped THC hits within minutes and tends to fade within one to three hours. Because you feel it fast, it's easier to gauge as you go.

Eaten THC works completely differently. It passes through your digestive system and liver first, which converts it into a related compound that's actually stronger and longer lasting. Onset is delayed, often 30 minutes to two hours, sometimes more, and once it kicks in it tends to stick around a lot longer than smoking does.

That delay is the number one reason people end up taking more than they meant to with edibles. The first dose doesn't seem to be doing anything yet, so a second goes down before the first has even peaked. Understanding this timing gap matters more for staying comfortable than almost anything else about THC.

Tolerance

Regular use trains your body to reduce the number of active CB1 receptors, so the same amount of THC delivers less effect over time. That's why frequent users often need more to feel what they used to, and why some people build in deliberate breaks to let their receptor sensitivity reset. More in [Cannabis Tolerance: What It Is and How to Manage It].

Who Should Be Especially Careful

Teenagers and young adults, since the brain keeps developing into the mid twenties and regular THC use during that window carries more risk to cognitive development than starting later in life.

Anyone with a personal or family history of psychosis or schizophrenia, where THC has a well documented association with higher risk specifically in that group.

Pregnant or breastfeeding people, since THC crosses the placenta and shows up in breast milk.

Anyone with a heart condition, since THC raises heart rate and cardiac demand.

Anyone about to drive or operate machinery. THC measurably slows coordination and reaction time while it's active, and driving under its influence is dangerous and illegal.

THC vs CBD

They get lumped together constantly, but functionally they're quite different. THC is intoxicating and binds directly to CB1. CBD isn't intoxicating and works through far more indirect routes. Full comparison in [CBD vs THC: What's the Actual Difference?].

Back to Gareth Prince, and THC's Legal Status in South Africa

Prince's fight actually started years before that 2012 arrest. In 1998, the Cape Law Society refused to admit him as a candidate attorney because of two prior cannabis possession convictions and his stated intention, as a practising Rastafarian, to keep using it for religious reasons. He took that all the way to the Constitutional Court in 2002 and lost, in a close, split decision. He kept practising his faith anyway, working as a legal advisor since he couldn't formally represent clients in court.

Then came the 2012 arrest at his home. That case became the vehicle for a much bigger constitutional challenge, and in 2018 the Constitutional Court ruled unanimously that criminalising the private use, possession and cultivation of cannabis by adults was unconstitutional. Deputy Chief Justice Raymond Zondo delivered the judgment. Prince was in the front row.

That ruling is the legal foundation South Africa still stands on. The 2024 Cannabis for Private Purposes Act built the practical rules on top of it. Here's where things sit now:

Private use, possession and cultivation by adults in a private setting is decriminalised.

THC itself is still classified as a Schedule 7 substance under the Medicines Act, the category for substances treated as having no accepted medical use outside specific therapeutic pathways, except when it's for approved therapeutic use, where it shifts to the more permissive Schedule 6.

Public use and commercial sale of cannabis for recreational purposes remain illegal. Legal commercial access currently runs almost entirely through the licensed medicinal channel regulated by SAHPRA, which is narrow and geared more toward export than everyday retail. Broader commercial rules are still being finalised.

So an adult using cannabis privately at home is standing on solid legal ground, twenty years after Gareth Prince first tried to get there. Buying or selling it commercially outside the licensed medical channel is still a live, unresolved legal question. Full detail in [Cannabis Laws in South Africa: What Is and Is Not Legal].

FAQ

What does THC stand for? Delta-9-tetrahydrocannabinol, the main psychoactive compound in cannabis.

Why do edibles feel so different from smoking? Your liver converts eaten THC into a stronger, longer lasting compound before it reaches your bloodstream, and it takes much longer to kick in, often 30 minutes to two hours. Smoked THC reaches your bloodstream almost immediately and fades faster.

Can THC cause anxiety instead of relaxation? Yes, especially at higher doses, for first timers, or with certain terpene and cannabinoid combinations. It's one of the most commonly reported downsides.

Is THC legal in South Africa? Private adult use is decriminalised, thanks largely to the case Gareth Prince fought for two decades. THC itself remains a controlled substance, and commercial sale for recreational purposes is still restricted outside the licensed medical channel.

Does THC show up on a drug test? Yes. THC and its metabolites are detectable on standard drug tests, and can stay detectable for days to weeks depending on how often you use and which test is being run.