Tetrahydrocannabinol (THC) has some potent effects against cancer, heart disease, pain, nausea, and insomnia. It can also help with seizures, insulin sensitivity and improve brain function in certain ways. Read on to learn more about THC and its benefits, as well as its side effects and other potential risks.

What is Tetrahydrocannabinol (THC)?

Tetrahydrocannabinol (THC), also known as delta9-tetrahydrocannabinol, is the primary component of cannabis responsible for its psychoactive properties. It is considered a secondary metabolite of the plant marijuana that serves as a defense mechanism to prevent consumption of the plant [1].

THC in the Cannabis plant needs to be heated in order to be efficiently utilized by the body [2].

Medical use of cannabis dates back as far as 16th century B.C. by the Egyptians, and subsequently by the Greeks and Romans. A cannabis extract containing THC metabolites was found inside a tomb in Israel on remains of a young woman who appeared to have died giving birth. The archeologists who discovered the tomb speculated that the cannabis was used to facilitate the birth process [3].

Current Uses of THC in Medicine

Although CBD may be a more popular constituent of cannabis for therapeutic purposes, synthetic forms of THC such as Dronabinol have been approved for the treatment of nausea, vomiting, and loss of appetite in chemotherapy and AIDS patients [4].

Nabiximols, a cannabis extract, is a spray that can ease the symptoms of other spastic symptoms of treatment-resistant multiple sclerosis [5].

Route of Administration and Pharmacokinetics of THC

There are many different routes of administration, with varying absorption and elimination rates, depending on the purpose of use [2].

  • Smoking or absorption of THC via the lungs results in rapid and efficient absorption with 2 – 56% bioavailability of THC and its metabolites. Peak levels in the blood are detected after 12 minutes.
  • Oral or ingestion of THC result in a lower, more gradual and blunted peak in serum concentration of THC. Serum levels peak at around 1.5 – 2 hours. Chocolate cookies with cannabis have ~6% bioavailability 1 – 5 hours post-ingestion. Absorbed cannabis is also subject to first-pass liver metabolism.
  • Sublingual, rectal, and skin uses of THC are somewhat less effective than smoking and injecting, but more effective than ingesting THC because these methods all bypass the digestive system and first-pass liver metabolism. In addition, the THC metabolites stay longer in the system when consumed via these less effective routes. Because smoking may cause other side-effects from smoke exposure, these other routes of administration may be favorable where a prolonged result is desired.

THC is a highly fat-soluble substance, which means that it has a preference for lipid-rich tissues such as lungs, hearts, brain, and liver [2].

Brain levels of THC are almost always higher than blood levels, and there may be THC in the brain even when it is absent in the blood. Chronic use of THC can result in THC accumulation in fat tissues [2].

THC readily crosses the placenta in dogs and sheep [6].

Clearance of THC involves CYP450 in phase II liver detoxification [7].

The Good: Health Benefits of THC

1) May Prevent Cardiovascular Disease

Marijuana use is typically associated with other unhealthy behaviors such as a high-calorie diet, smoking, and other drug use. However, mechanistic studies found that THC itself (without those unhealthy lifestyle factors) have shown that THC may help reduce cardiovascular disease risk [8].

THC Hinders Progression of Atherosclerosis Plaque

Patients developing atherosclerosis or hardening of arteries have increased levels of foam cells in the major arteries which lead to deposition of cholesterol and fatty plaque [9].

CB2 receptors are present on the surface of foam cells that THC activates, preventing them from depositing fatty streaks in the heart [10, 11].

In rats, similar results were shown through supplementation of low levels THC to reduce atherosclerosis without psychoactive effects [12].

THC inhibits the 15-lipoxygenase enzyme, which is an enzyme that oxidizes low-density lipoprotein [13].

THC’s anti-inflammatory effects reduce platelet accumulation and promote immune function in the heart, which inhibits atherosclerosis [14].

2) May Inhibit Tumor Growth and Help Prevent Cancer

Brain Cancer

Glioblastoma multiforme is a deadly and hard to treat a form of brain cancer with limited treatment options and a low life expectancy. Direct injection of THC into the glioblastoma tumors inhibits tumor cell proliferation and increased the median life expectancy by about 24 weeks [15]. A cellular study found that CBD enhances this effect of THC [16].

Breast Cancer

Treatment of breast cancer cells in mice showed that low doses of THC (0.5 mg/day) served significant anti-tumor properties. THC reduced growth, number, and overall blood vessel number in the breast tumors [17].

In mice, THC also successfully inhibits ErbB2-driven breast cancer through inhibition of Akt and mTOR signaling pathways [18].

However, THC use may not be beneficial in breast cancer types that do not harbor cannabinoid receptors. In addition, THC may suppress anti-tumor immune responses [19].

Lung Cancer

THC inhibits EGF-induced lung cancer cell migration in cell lines and metastasis in mice [20].

In a survey of people who are habitual THC users but not cigarette smokers, the use of THC did not increase the incidence of lung cancer, although negative outcomes from smoking THC were not ruled out [21].

Prostate Cancer

The interplay between cannabinoid receptors and prostate cancer prognosis is complex. Some studies found that THC inhibits cell growth, while others found it enhances cell growth [22].

3) Stimulates Appetite and Can Help With Nausea

In patients suffering from HIV, cancer or other diseases that lead to decreased appetite and muscle wasting, THC and other cannabis substances has been studied as an effective treatment to stimulate appetite and mitigate cachexia [23].

In HIV patients, increased intake of THC through inhalation reduced the levels of peptide PYY (an appetite suppressant), while increased levels of leptin and ghrelin [24].

4) Helps with Pain Management

In mice, THC may have a pain relieving effect by potentiating the glycine receptor, including neuropathic pain [2526].

However, human studies showed mixed results regarding THC’s effectiveness for pain management [27, 28].

Mice that consumed THC increased the activity CB1 receptor and release of the agmatine. The release of agmatine increased pain tolerance while also increasing overall body temperature [2930].

Multiple Sclerosis

Oral ingestion of THC in patients suffering from multiple sclerosis (MS) reduced symptoms. The maximum dosage of 25 mg of THC over the course of 15 weeks reduced pain and muscle stiffness. Also, perceived notions of healing in patients with MS increased after taking THC, improving the quality of life [313233].

5) Can Help Insomnia and Increase Deep Sleep

Cannabis and THC administration appears to decrease the time it takes to fall asleep and increase stage 4 sleep, but decrease REM sleep [34].

6) Helps Prevent Seizures

In a rat model, THC completely abolishes epileptic seizures [35].

7) Increases Insulin Sensitivity

An epidemiological study found that current marijuana use is associated with 16% lower fasting insulin levels in comparison to past marijuana users and 26% in comparison to people who never used marijuana. This trend was also similar for other insulin resistance metrics, suggesting that THC increases insulin sensitivity [36].

On the other hand, in both mice and humans, blocking the cannabinoid receptor 1 increases insulin sensitivity in an adiponectin-dependent manner [3738].

8) THC Can Improve Your Brain in Some Ways

Chronic THC exposure in mice results in increased brain-derived neurotrophic factor (BDNF) in the hippocampus, but not in the frontal lobe [39].

Marijuana smoking increases cerebral blood flow both acutely and 2 hours afterward [40, 41].

Alzheimer’s Disease

THC has been shown to reduce amyloid plaque levels, reduce inflammation, and improve mitochondrial function in cellular models [42, 43].

9) Causes Euphoria

THC causes euphoric state through increasing dopamine, although the chronic use of THC can blunt the dopamine receptors (coded by DRD1 and DRD2 genes) [44]. The effects of THC on the dopamine system appears to be dependent on dose and duration of use [44].


5-HT1A agonists enhance the CB1 receptor-mediated effects of THC [45].

When THC is present with Cannabidiol (CBD), it appears that CBD modulates the effects of THC on the CB1 and CB2 receptors [46]. CBD itself is not psychoactive.

Other Considerations

The Bad: Adverse Effects of THC

THC can cause schizophrenia-like symptoms, altered perception, increased anxiety, delayed recall time, impaired mental performance, and increased cortisol [47].

After ingesting a high dose of THC, increased levels of adrenaline were detected after 2 hours but then returned to normal after 4 hours [48].

Cannabinoid use can impair working memory through the CB1 receptor in astroglial cells [49].

Chronic consumption of Cannabis increased the odds of getting Bipolar disorder and manic episodes [50].

THC may reversibly block synaptic neuroplasticity in the nucleus accumbens and hippocampus [51].

Chronic THC usage in humans reduces overall dopamine synthesis which in turn reduces motivation [52].

Highly potent cannabis may impair creativity and divergent thinking [53].

Repeated use of cannabis can result in intolerance due to a reduction in CB1 receptors [54].

Prior THC exposure can make nicotine more addictive in rats [55].

Want Better Ways to Improve Your Mood?

If you’re interested in natural and more targeted ways of improving your mood, we at SelfHacked recommend checking out this mood wellness report. It gives genetic-based diet, lifestyle and supplement tips that can help improve your mood. The recommendations are personalized based on your genes.

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About the Author

Nattha Wannissorn - PHD (MOLECULAR GENETICS) - Writer at Selfhacked

Nattha Wannissorn, PhD

PhD (Molecular Genetics)

Nattha received her Ph.D. in Molecular Genetics from the University of Toronto and her undergraduate degree in Molecular and Computational Biology from the University of Pennsylvania.

Aside from having spent 15 years in biomedical research and health sciences, Nattha is also a registered holistic nutritionist, a certified personal trainer, has a precision nutrition level 1 certification, and is a certified functional diagnostic nutrition practitioner. As a holistic practitioner with a strong science background, Nattha is an advocate of science literacy in health topics and self-experimentation.

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