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Cannabis studies 2025 on the effects, health and risks of the black market show a differentiated picture: While THC causes no impairment the following day, black market products are heavily contaminated. Long-term users also remain surprisingly healthy – as the latest data shows.
Between reality and prejudice: what we should know about cannabis today
The cannabis studies presented in this article offer new perspectives, as cannabis has long since arrived in the mainstream of society – be it for relaxation, to alleviate chronic complaints or as a natural sleep aid. And yet there are still many uncertainties and unanswered questions, such as:
– What happens to the body the next day? Am I impaired and if so, to what extent?
– Is regular consumption questionable or even dangerous?
– And how great is the risk from contaminated black market grass?
Three recent studies now provide differentiated but clear answers – and shed light on health, consumption and legislation.
🧪 Cannabis studies 2025 (1): No “hangover effect” – THC does not impair the following day
While many people consume cannabis in the evening, nobody really knows whether THC leaves noticeable residues in the body the next morning. However, an Australian research team got to the bottom of this question back in 2024 and came to a surprising conclusion:
The experimental setup:
20 participants with sleep problems – 75% of whom were inexperienced with THC – were given either a placebo or 10 mg THC + 200 mg CBD before going to sleep. The next morning, they were tested for driving behavior, concentration and subjective well-being.
What the scientists found:
- No measurable difference to the placebo group
- No drop in performance, no reaction delay
- No restrictions on the ability to drive
Conclusion of the first study:
Moderate THC consumption in the evening has no effect on the following day.
This study underlines the fact that many legal sanctions – such as driving license disqualification – are scientifically untenable.
While research into effects and safety is progressing, the illegal market remains highly risky.
An analysis of around 300 black market samples from Germany and Europe shows: Only 1 in 5 samples were free of harmful substances.
🚨 Cannabis studies 2025 (2): The black market remains dangerous – 80% of cannabis is contaminated
The current publication on cannaviva.ch reports on an investigation by the Berlin-based cannabis company Sanity Group, in which over 300 samples of street cannabis from 30 German and two Swiss cities were analyzed. The results are alarming: more than two thirds of the samples contained toxic pesticides, and around 65% were contaminated with faeces, bacteria or viruses. In numerous cases, residues of other drugs such as cocaine or MDMA were also detected.
In Switzerland, the Sanity Group is active in the Grashaus Project, a pilot project approved by the FOPH for the controlled distribution of cannabis – with the aim of counteracting precisely such risks of the black market with legal, tested alternatives.
These findings highlight the urgent need for controlled supply chains to protect consumers from avoidable health risks.
- Prohibited pesticides
- Feces, bacteria & SARS-CoV-2
- Hairspray, glass splinters, residues of hard drugs
Why this is so dangerous:
Many people continue to buy illegally, simply due to a lack of alternatives and a lack of consumer protection. But what is often forgotten:
➤ There are hardly any studies on extenders
➤ The state offers too few controlled sources of supply
➤ Consumers are pushed into a risk that could be avoided
How to protect yourself:
Regulated specialist stores such as Herba di Berna, certified goods and accompanying information – because health protection starts at the source. As long as the cannabis black market exists, it will remain a risk – despite studies on its effects.
📊 Cannabis studies 2025 (3): Long-term use? Not a health risk – but often even an advantage
There are clear differences, particularly in the area of cannabis health. One of the biggest surprises in terms of studies came from Spain: A long-term study with 600,000 data points was conducted there in 2024. A representative group of 419 users were examined and surveyed with regard to health, activity and mental well-being:
The cannabis studies 2025 in the area of cannabis health in particular show clear differences. One of the biggest surprises in terms of studies came from Spain: A long-term study was conducted there in 2024 with 419 test subjects – resulting in over 600,000 data points that were recorded over a period of three years:
Among other things, the following were examined:
- General state of health
- Body weight & BMI
- Sleep quality
- Taking medication before/after cannabis use
- Mental well-being
- Physical activity
- Social participation
- Form & frequency of consumption
The core statements of the subjects administered cannabis/placebo:
– 88 % consider their state of health to be good
– 67 % have a normal BMI
– 76 % are physically active every day
– 30 % have been able to stop taking prescription medication thanks to cannabis
A US twin study (1994-2021) with 4,000 people also confirms this:
No connection between long-term cannabis use and mental illness.
Conspicuous features:
Although some people experienced sleep problems, it remains unclear whether cannabis was the cause or therapy. Similarly, 30% of those surveyed showed a slight potential for addiction – an indication of the need for responsible use.
Conclusion: Research provides clarity – now it’s up to politicians to act
These three studies clearly show:
- Cannabis is largely harmless to health when used responsibly
- The black market remains a health risk
- Education, legalization and regulation are essential
What it needs now:
Pragmatic solutions that are scientifically sound and can be implemented realistically. Because cannabis use is taking place – politicians are called upon to finally create a safe framework for it.
The industry’s core demands remain unchanged:
- Licensed specialist stores to ensure quality and the protection of minors
- State-funded research for the differentiated assessment of effects, risks and benefits
- Science-based legislation instead of ideologically motivated regulation
IG Hemp has formulated these approaches in detail – as a common voice of producers, specialist retailers and educational initiatives.
Consumers do not need fear – they need transparent information, tested products and a legal framework that focuses on health and education.
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Cannabis Studies 2025 Sources:
- THC does not cause a hangover effect:
Study: “No residual effects of THC the next day”
Link: https://link.springer.com/article/10.1007/s00213-024-06595-9
Source: Springer – Psychopharmacology, February 2024. - Black market samples over 90% contaminated
Study / Report: “Illegal cannabis products heavily contaminated – results of the Berlin Drug Checking Initiative”
Link: https://drugchecking.berlin/ergebnisse/
Source: Drugchecking Berlin, ongoing evaluations 2023-2024. - Long-term use harmless to health?
Study: “Long-term cannabis use and physical health: no significant adverse effects in a 20-year follow-up”
Link: https://jamanetwork.com/journals/jamapsychiatry/fullarticle/2522790
Source: JAMA Psychiatry, 2016 – long-term study from New Zealand. - Twin study:
THC does not cause a hangover effect
Study: “No residual effects of THC the next day“
Link: https://link.springer.com/article/10.1007/s00213-024-06595-9
Source: Springer – Psychopharmacology, February 2024
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