Delta-9-tetrahydrocannabinol (THC) is considered the primary psychoactive component of cannabis and is sought after by many recreational users and medical patients who hope to experience medicinal effects, relaxation, or creative inspiration. However, while occasional use is socially tolerated or even perceived as harmless in some contexts, recent epidemiological and clinical studies show that regular use of high-potency THC may be associated with serious health consequences.

In this article, we examine the current scientific evidence regarding the physical, mental, and social risks associated with regular consumption of high-THC cannabis—with a focus on verifiable biological mechanisms.

At the same time, this article aims to spark some reflection: moving away from the industrially driven high-THC model and back to more balanced strain profiles that allow for a more harmonious interaction of active compounds—the so-called entourage effect*¹.

^*1The entourage effect describes the combined action of cannabinoids, terpenes, and other phytochemicals. More details on this will follow in Sections 5 and 6.

The potency of cannabis products is primarily measured by their THC content – and this figure has been on a clear upward trend for decades.

While confiscated plant material (which is not as representative as modern samples) frequently had THC levels of around 4% in the 1990s (El Sohly et al., 2016 – https://pubmed.ncbi.nlm.nih.gov/26903403/), modern cultivars today often range from 15–25 %. The trend is even more dramatic for extracts, which can reach concentrations of 60–90% THC (Chandra et al., 2019 – https://pubmed.ncbi.nlm.nih.gov/30671616/).

The key risk, however, lies less in the THC content itself than in the imbalance of active compounds. While CBD levels in many modern strains have been significantly reduced over the decades, the ratio of THC to CBD has shifted markedly in favor of THC (Freeman et al., 2020 – https://pubmed.ncbi.nlm.nih.gov/33160291/).

In the absence of CBD, the modulating antagonist, highly concentrated THC interacts with the endocannabinoid system, which becomes increasingly more strongly stimulated. Without a certain balance provided by other cannabinoids and terpenes, the effects of cannabis can shift in a potentially problematic direction.

Even in the short term, consuming high doses of THC can trigger a range of physiological and psychological effects:

• Impaired cognition, coordination , and judgment – particularly relevant in traffic
• Temporary mental reactions such as anxiety, paranoia or panic attacks
• Cardiovascular effects such as tachycardia (rapid heartbeat) and changes in blood pressure

These effects are usually temporary, but they can be significantly more intense at high doses or in sensitive individuals.

Psychosis and Schizophrenia

One frequently studied association involves the regular use of high-potency THC products and the risk of psychotic episodes.

Several studies show that high THC exposure is associated with an increased risk of psychosis or schizophrenia (Di Forti et al., 2019 – https://pubmed.ncbi.nlm.nih.gov/30902669/). The combination of high potency, frequent use, and individual vulnerability appears to be particularly relevant in this context.

Depression, Anxiety, and Other Disorders

Regular use is also associated with higher rates of anxiety disorders, depression, and mood swings.

It is important to take a nuanced view here: According to the current state of research , cannabis is generally not considered the sole cause of such conditions. However, in people with a corresponding vulnerability or genetic predisposition , it can be a significant trigger.

This means that cannabis does not necessarily trigger the aforementioned psychiatric conditions, but it can exacerbate existing disorders or contribute to their initial onset. Science refers to this as the “component-cause model” – cannabis is a piece of the puzzle that completes the picture when a predisposition is present. This distinction is essential, as politicized discussions often claim that cannabis is the sole cause of such conditions – a simplification that is scientifically untenable.

Long-term studies suggest that regular use of high doses of THC can impair memory, attention, and executive function. These effects are particularly relevant for adolescents and young adults, as the human brain continues to develop until around the mid-twenties.

The earlier the onset and the higher the doses of THC consumed, the greater the risk of long-term or potentially persistent cognitive impairment.

Of course, minors should generally not use cannabis – but the reality is different. That is precisely why the debate over high-THC products particularly affects younger consumers and should be critically examined.

Only through open communication and honest education can we counter the trend toward ever-higher THC levels in the long term. An industry driven primarily by economic interests should not be the sole determinant of which consumption patterns take hold in an entire community .

Now that we’ve looked at what can happen when THC strongly stimulates the system, an obvious question arises: Is there another way?

This is where the entourage effect comes into play. The term, coined by cannabis pioneer Raphael Mechoulam, describes the synergistic effect of the entire plant – the idea that the interaction of the compounds is biologically more relevant than isolated individual compounds (Russo, 2011 – https://pubmed.ncbi.nlm.nih.gov/21749363/).

In many modern high-THC strains, however, this balance has been significantly altered. Instead of a complex profile of active compounds, a single compound often dominates: THC.

A more balanced profile, on the other hand, relies on multiple levels of modulation:

Modulation Instead of Maximization

Phytochemicals such as CBD, terpenes, or minor cannabinoids (e.g., CBG or CBN) can partially modulate the effects of THC. Some of these compounds, for example, indirectly influence the binding of THC to CB₁ receptors or act via other neurobiological signaling pathways.

Full-Spectrum Instead of Isolate

Clinical observations suggest that patients may benefit more from certain applications of full-spectrum extracts than from isolated synthetic THC such as dronabinol. A broader matrix of active compounds often appears to be better tolerated (Russo, 2019 – https://pubmed.ncbi.nlm.nih.gov/30687364/).

In short: A diverse mix of active compounds provides the endocannabinoid system (Kilaru et al., 2020 – https://pubmed.ncbi.nlm.nih.gov/32648908/ ) more nuanced signals rather than stimulating it exclusively with high doses of THC. Especially in cases of medical or long-term use, more balanced active ingredient profiles can therefore be significantly better tolerated.

A study by Finlay et al. (2020 – https://pubmed.ncbi.nlm.nih.gov/32269529/ ) sparked debate when it showed that many common terpenes hardly interact directly with CB₁- or CB₂-receptors.

Some critics were quick to interpret this as a refutation of the entourage effect. However, this conclusion is too simplistic, as the effect cannot be explained solely by cannabinoid receptors.

The mechanism of action of cannabis is best understood as a multidimensional network.

For example, terpenes can affect other neurobiological systems:

• Interactions with GABA receptors, which may support calming effects
• Factors influencing serotonin signaling pathways associated with mood and anxiety regulation
• Modulation of TRP channels, which are involved in pain transmission and inflammatory responses

In other words: Even if a terpene does not bind directly to the CB receptor, it can still exert relevant effects through other neurobiological systems and thus influence the overall effect of cannabis.

There is also an important methodological issue in this research. Experiments with isolated terpenes in cell cultures can only partially replicate what happens in the complex chemical matrix of a natural flower (André et al., 2024 – https://pubmed.ncbi.nlm.nih.gov/39598452/).

A post-harvest “spraying” of low-quality flowers with external terpenes – a practice occasionally observed in the context of so-called Cali weed*² or PGR-Grow*³ – cannot realistically reproduce this natural active compound architecture.

*²Cali-Weed: Cali-Weed is the term commonly used today for high-priced buds, often associated with eye-catching, colorful packaging. Marketing takes center stage here, while the quality generally leaves something to be desired. Often small, hard, round buds, frequently resulting from the use of PGRs*³ during cultivation. Also known internationally as “spray packs.”

*³PGR-Grow (Plant Growth Regulators): Synthetic growth regulators (not fertilizers!) that interfere with the plant’s hormonal balance to artificially increase flower density and weight. Their use is considered highly hazardous to health, particularly in smokable products, as substances such as paclobutrazol or daminozide release carcinogenic (cancer-causing) and liver-toxic residues when burned. Due to this toxicity and the simultaneous reduction in terpene quality, their use is usually strictly prohibited in regulated markets.

From a breeding perspective, it is relatively easy to focus on phenotypes that produce a particularly high number of trichomes and consequently yield high THC levels. However, it becomes far more exciting when the focus shifts to terpene-rich phenotypes.

In such selection processes, the primary focus is not on trichome density, morphology, stretch, or maximum yield. Instead, selection is consistently based on aromatic profiles – specifically on the intensity, complexity, and development of aromas during growth.

A classic technique in this early selection process is the so-called stem rub. This involves gently rubbing the stem or a side shoot of the plant between the thumb and index finger, which releases volatile aromatic compounds. This method provides the first indications of the future terpene profile of a plant as early as the vegetative phase.

With particularly aromatic strains – such as Tangie – the stem rub can predict the flowers’ eventual aroma profile with surprising accuracy. During the flowering phase, the terpenes continue to develop and usually stabilize around the sixth week of flowering into a largely final aroma profile.

A breeding strategy that prioritizes terpene profiles has another important effect: It can bring back traits that have been overshadowed in many modern high-THC strains. Through years of selection for a few dominant traits – primarily THC potency and flower density – numerous genetic variants have become recessive or have completely disappeared from many lines.

This phenomenon is described in population genetics as the bottleneck effect and leads, in the long term, to a narrowing of the gene pool. A return to aromatic diversity and older lines can therefore not only produce new flavor profiles, but also reintegrate lost genetic traits into modern breeding programs.

Fig. 2: Bottleneck effect.
Photo: Tsaneda / Wikimedia Commons (CC BY-SA 3.0).
https://commons.wikimedia.org/wiki/File:Bottleneck_effect.jpg

Regular use of high-potency THC products may be associated with a wide range of potential risks—from acute psychological effects and cognitive impairments to an increased risk of certain psychiatric disorders in vulnerable individuals.

At the same time, there is strong evidence to suggest that more balanced active ingredient profiles – that is, products with a broader spectrum of cannabinoids and terpenes – are often better tolerated than variants with a high THC content.

A market defined almost exclusively by ever-higher THC levels also poses additional risks for younger consumers, particularly for people under the age of 25, whose brains are still developing.

This leads to an obvious conclusion: rather than breeding solely for potency, a return to genetic diversity, traditional strains, and so-called True Breeds*⁴ could benefit both the plant and the community in the long run.

Quality isn't defined solely by THC percentages. A more sustainable approach to cannabis means taking the plant's complexity seriously – not just its most potent active ingredient.

*⁴True Breeds: See article https://qtgenetics.com/true-breeding-vs-industrie-trends-den-cannabis-genpool-retten/

André, C. M., Hausman, J. F. & Guerriero, G. (2024). The Entourage Effect in Cannabis Medicinal Products: A Comprehensive Review. Pharmaceutics, 17(11), 1543. https://pubmed.ncbi.nlm.nih.gov/39598452/

Chandra, S., Radwan, M. M., Majumdar, C. G., et al. (2019). New trends in cannabis potency in USA and Europe during the last decade (2008–2017). European Archives of Psychiatry and Clinical Neuroscience, 269(8), 997. https://pubmed.ncbi.nlm.nih.gov/30671616/

Di Forti, M., Quattrone, D., Freeman, T. P., et al. (2019). The contribution of cannabis use to variation in the incidence of psychotic disorder across Europe (EU-GEI): a multicentre case-control study. Lancet Psychiatry, 6(5), 427–436. https://pubmed.ncbi.nlm.nih.gov/30902669/

ElSohly, M. A., Mehmedic, Z., Foster, S., et al. (2016). Changes in Cannabis Potency Over the Last 2 Decades (1995–2014): Analysis of Current Data in the United States. Biological Psychiatry, 79(7), 613–619. https://pubmed.ncbi.nlm.nih.gov/26903403/

Finlay, D. B., Sircombe, K. J., Nimick, M., et al. (2020). Terpenoids from Cannabis Do Not Mediate an Entourage Effect at Cannabinoid Receptors. Frontiers in Pharmacology, 11, 359. https://pubmed.ncbi.nlm.nih.gov/32269529/

Freeman, T. P., Craft, S., Wilson, J., et al. (2020). Changes in delta-9-tetrahydrocannabinol (THC) and cannabidiol (CBD) concentrations in cannabis over time: systematic review and meta-analysis. Addiction, 116(5), 1000–1010. https://pubmed.ncbi.nlm.nih.gov/33160291/

Kilaru, A. & Chapman, K. D. (2020). The endocannabinoid system. Essays in Biochemistry, 64(3), 485–499. https://pubmed.ncbi.nlm.nih.gov/32648908/

Russo, E. B. (2011). Taming THC: potential cannabis synergy and phytocannabinoid-terpenoid entourage effects. British Journal of Pharmacology, 163(7), 1344–1364. https://pubmed.ncbi.nlm.nih.gov/21749363/

Russo, E. B. (2019). The Case for the Entourage Effect and Conventional Breeding of Clinical Cannabis: No “Strain,” No Gain. Frontiers in Plant Science, 9, 1969. https://pubmed.ncbi.nlm.nih.gov/30687364/