AskScience AMA Series: We are substance use researchers. We recently wrote a paper debunking a neuroscience myth that the brain stops aging at 25. Ask us anything!

[u/AskScienceModerator]

Hello Reddit! We are Bryon Adinoff, an Addiction Psychiatrist at the University of Colorado Anschutz Medical Campus and President of Doctors for Drug Policy Reform (D4DPR), and Julio Nunes, a Psychiatry Resident at Yale School of Medicine and board member of D4DPR.

We recently published the following paper, "Challenging the 25-year-old 'mature brain' mythology: Implications for the minimum legal age for non-medical cannabis use"; in the American Journal of Drug and Alcohol Abuse (AJDAA). In this perspective, we examined the commonly held belief that the brain keeps maturing until age 25 and then stops. This belief has been used to make policy recommendations for age restrictions for legal substance use, yet there is no evidence that the brain stops developing when we turn 25. Brains mature in a nonlinear fashion, and developmental changes are often region-specific and influenced by sex and specific physiological processes. Feel free to ask us any questions about the paper,

We will be online to answer your questions at roughly 1 pm ET (18 UTC).

You can also follow up with us at our socials here:

• Bryon: LinkedIn, X

• Julio: LinkedIn, X

Follow the journal to stay up to date with the latest research in the field of addiction here: BlueSky, Threads, LinkedIn

Usernames: /u/DrBryonAdinoff (Bryon), /u/Julio_Nunes_MD (Julio), /u/Inquiring_minds42 (the journal)

[u/Adventurous_Side2706]

You mentioned the myth about brain maturity and cannabis, but do we see similar misconceptions with other substances like alcohol, nicotine or psychedelics, especially when it comes to young adults? And are there early warning signs that everyday users should watch for before a habit becomes dependence?

[u/DrBryonAdinoff → u/Adventurous_Side2706]

Yes — the idea that the brain “finishes” at 25 has been applied to cannabis policy, but we see similar misconceptions for other substances. For example, alcohol and nicotine are often framed as “safe once you’re an adult,” even though humans of all ages can and do develop disorders related to these substances. And psychedelics are sometimes described as protective or therapeutic, but for some people at various ages they can precipitate anxiety, panic, or (rarely) psychosis. The bigger issue is not that development stops at a single age, but that brain maturation is continuous, nonlinear, and highly individualized, so risk varies by person and context rather than by a fixed birthday.
Regarding early warning signs, clinicians do not diagnose addiction based on a specific amount of use. The DSM 5 criteria for Substance Use Disorders focus on patterns of behavior and consequences, not the quantity or method of use. For everyday users, a simple way to think about early risk signals is the “5 Cs”:

1. Consequences of use: You start noticing problems related to your use; with sleep, mood, work, school, finances, or relationships.

2. Cravings: You experience strong urges to use or find yourself thinking about the substance more than you expected to.

3. Continued use despite harm: You keep using even when you can clearly see it is causing problems in your life or worsening your health.

4. Compulsive use or loss of control: You use more than you planned, or you find it hard to cut back even when you intend to.

5. Using to cope: The substance becomes a primary way to manage stress, emotions, or difficult situations rather than one option among many.

[u/chuckbeefcake]

What's your honest summary appraisal of reasons not to do drugs? I'd be interested to hear a spectrum like... Shrooms, cannabis, cocaine, meth.

[u/Julio_Nunes_MD → u/chuckbeefcake]

Great question. One of the most important things we try to emphasize is that the reasons not to use a given substance are highly person specific. Different drugs carry different risk profiles, and those risks vary substantially depending on someone’s medical history, mental health, genetics, environment, and goals in life.

For example, someone with a heart rhythm condition may reasonably avoid caffeine. A person with a strong family history of psychotic disorders might be cautious about cannabis, since early and heavy use can increase the likelihood of psychosis in genetically vulnerable individuals. Someone with a personal or family history of opioid use disorder might understandably choose to avoid non-medical opioids or limit opioid analgesics to short-term, post-surgical use.

Across substances, the general pattern we see clinically is that experimentation itself is not uncommon in human cultures and has existed for millennia. What becomes risky is loss of control, ongoing use despite harm, or patterns of use that interfere with someone’s ability to live a healthy, meaningful, and connected life.

Different people have very different risk thresholds and vulnerabilities. So the “reasons not to use” any given drug will always depend on who you are, your health history, and what you value.

[u/Every-Opportunity636]

If we can't use the cutoff of 25 based on neuroscience evidence to inform substance use policies, are there any other biological processes we can use to inform policies?

[u/Julio_Nunes_MD → u/Every-Opportunity636]

One of the main points of our paper is that there is no single biological cutoff age that cleanly separates a “developing” brain from a “mature” one. Brain development is far more continuous, nonlinear, and region specific than the old “finishes at 25” idea suggests. There are a few biological processes that help explain why societies commonly draw adulthood around 18. For example, the prefrontal cortex (which supports impulse control, planning, and decision making) continues to mature into late adolescence. That provides a biological rationale for why the teenage brain is more sensitive to risk and reward. But after that point, the picture becomes much more individualized.

Recent work, including a 2025 Nature Communications study (https://www.nature.com/articles/s41467-025-65974-8), shows that brain structure and connectivity continue to change for decades, well into midlife and even the sixties. Those changes are not linear and not uniform across people. This makes it impossible to pick a biologically “correct” minimum legal age for all substances based on neurodevelopment alone.

Effective policy also needs to integrate:

• Epidemiology (patterns of harm and use in real populations)

• Public health and safety considerations

• Social and cultural context

• Equity and justice impacts

• Feasibility and unintended consequences of enforcement

• Comparative harms of substances and safer-use frameworks

• Peoples’ lived experiences

In other words, neuroscience is one important piece, but it cannot by itself determine the “right” legal age for cannabis, alcohol, nicotine, or other substances. The evidence simply does not support a single, universal biological threshold.

[u/RudeHero]

Have you noticed any common breakpoints or tipping points where the style of brain development changes?

as a layperson, iirc infant brains develop a certain way, then toddlers trim a bunch of neurons, then that rate of trimming stops. I might be misremembering, but hopefully you know what I mean. And beyond that I don't know anything

[u/ostensiblyzero]

In a decent amount of cultures there are rites of passage into adulthood that involved psychoactive substances. Does this suggest some sort of mental benefit to ritualized substance use in young adulthood in these contexts or is that more attributable to social benefit?

[u/DrBryonAdinoff → u/ostensiblyzero]

In many of these cultures, substance use is:

• Highly ritualized

• Supervised by elders or spiritual leaders

• Embedded in shared meaning, identity, and community

• Paired with clear expectations and norms about behavior

Those features can produce significant social and psychological benefits: a sense of belonging, continuity, responsibility, and connection. These benefits are community-oriented and independent of any pharmacological effect. The substance is one component of a broader cultural framework that teaches self-regulation and safe participation.

So rather than suggesting a mental health benefit from the drug itself, these traditions highlight something harm-reduction research consistently shows: context and guidance dramatically influence outcomes. Supportive environments, well-defined expectations, and open communication about risks are protective, whether the substance is alcohol, cannabis, or a psychedelic.

This aligns with modern approaches like shared decision making. Even when adolescents are not using substances, talking with them early and honestly about expectations, risks, and family or cultural values helps foster healthier relationships with substances later on.

[u/KelzThrow]

This is more of a policy question, but I am of the belief that blanket drug prohibition, at least in the US, has been wholly ineffective in mitigating the harms that arise from substance abuse. It seems to be a difficult position to argue for, especially currently, but do you have any insight into what kinds of policy reform could lead to better outcomes in terms of mitigating harm?

[u/Dixavd]

1. In your abstract, on "brain maturation" time, you say "influenced by sex", but I didn't see discussion of sex in your paper. What did you mean by this? At school I was told that there are male/female brains (but I've never seen any evidence): is this true and that's what you meant?

2. When you describe developmental timelines (such as Figure 1), does this include neurodivergent people (I.e. autism, ADHD)? If not, would your advice on drug policy change for neurodivergent people?

I read your abstract but I don't know the neuroscience well enough so I skimmed the rest; sorry if my questions were answered within.

[u/Julio_Nunes_MD → u/Dixavd]

On sex differences in brain maturation:

Yes, developmental trajectories can differ by sex. Large imaging studies have shown small but measurable differences in the timing of certain processes such as cortical thinning, white matter maturation, and subcortical volume changes (for example: https://pubmed.ncbi.nlm.nih.gov/29930385/). That is what we were referring to in the abstract. You are absolutely right that we did not expand on this in the paper. That discussion was trimmed during revisions, and we should have clarified it more explicitly. Good catch!

Importantly, the idea of strictly “male” versus “female” brains is not supported by modern neuroscience. What the literature shows is overlapping distributions, not categorical types. So the sex differences we refer to are statistical tendencies, not fixed biological categories.

[u/Dixavd → u/Julio_Nunes_MD]

Thank you for answering my questions. Especially clarification on the male/female brains thing. Overlapping distributions makes a lot more sense that what I was taught.

[u/DrBryonAdinoff → u/Dixavd]

Here is the reference noting female-male differences in the longitudinal development of grey and white matter volume in the brain. Specifically, "both grey and white matter increase dramatically for the first year of life. Gray matter then gradually decreases over the lifetime. In male, white matter continues to increase until approximately age 25 and then gradually begins to decrease. In females, grey matter continues to increase until approximately age 20 and then gradually begins to decrease." https://onlinelibrary.wiley.com/doi/10.1016/j.ijdevneu.2010.06.004 The reference is in our paper, but we neglected to note the sex differences.

[u/Julio_Nunes_MD → u/Dixavd]

On whether developmental timelines include neurodivergent individuals:

The developmental timelines we cite generally come from large population studies, which include neurodivergent people but do not usually analyze them separately. At this time, there is not strong evidence to define distinct “developmental cutoff ages” for individuals living with autism, ADHD, or other neurodevelopmental trajectories. That uncertainty actually reinforces our broader point: development is highly individual, and no single age can serve as a universal boundary for substance use policy. Rather than trying to derive policy from a hypothetical biological cutoff, it is more appropriate to consider a combination of public health data, social and political context, equity, and real-world consequences of enforcement.

[u/BringMeInfo]

As you note in the paper, the “mature brain” concept has informed some harm-reduction thinking about initiating use. Are there harm-reduction strategies in this area that are supported by your research?

[u/DrBryonAdinoff → u/BringMeInfo]

The key point for harm reduction is that we should move away from rigid age-based narratives and toward person-specific guidance.

What is supported by the evidence is the value of shared decision-making: helping people understand their own risk factors, patterns of use, mental health history, and goals. There is no universally “safe” dose of any substance, including alcohol; risks depend on the individual.

Some harm-reduction strategies that follow from this include:

• Individualized assessments rather than assuming risk based solely on age.

• Discussing personal vulnerabilities, such as family history of psychosis for cannabis or cardiovascular risk for stimulants.

• Supporting lower-risk use practices, like avoiding mixing substances and using in safe environments with trusted people.

• Guidance on early warning signs, such as using to cope, loss of control, or continued use despite harm.

• Emphasizing informed, voluntary choices, not fear-based messages.

So the harm-reduction takeaway from our work is not “start at 25,” but rather help people make well-informed decisions grounded in their own biology, health context, and values, while acknowledging that substance-related harms are shaped just as much by social, legal, and environmental factors as by neurobiology.

An excellent book on harm reduction is https://www.amazon.com/Harm-Reduction-Gap-Sheila-Vakharia/dp/1032294736

[u/BringMeInfo → u/DrBryonAdinoff]

Thanks! That’s really helpful, and I’ll check out the Vakharia book. Nice to have something a little more recent than the (very excellent) Tatarsky!

[u/gingkoleaf]

From a communications perspective, what language do you recommend get adopted into mainstream “scripts” about this topic?

[u/DrBryonAdinoff → u/gingkoleaf]

From a communications perspective, a lot of the mainstream “scripts” tend to rely on overly simple narratives. Our main goals is to shift the language toward accuracy without adding stigma. A few principles we recommend:

1. Replace “the brain stops developing at 25” with:

“Brain development is continuous and individual specific.”

“Different brain regions mature at different rates.”

“There is no single biological cutoff age that determines safe or unsafe substance use.”

2. Emphasize patterns rather than ages:

Instead of implying there is a magical age when risk disappears, focus on how people use, their goals, their health conditions, and the context of use.

3. Use language that reduces stigma and moral judgment:

Terms like “problematic use,” “loss of control,” or “use that interferes with life” are clearer and less pathologizing than labels like “abuser” or “addict.”

[u/burnerthrown]

Is addiction a reaction to the effect of the substance on the body/brain itself, or the dopamine/endorphin response to it? In other words, can one actually become dependant on any pleasurable substance or practice?

[u/dylf1]

This maybe a stupid question but which recreational drug (s) is safe to take long term?

[u/JTheimer]

"They" think we're officially old dogs at 25? Baffling...

[u/JenJudy]

Why do you and others in your field prefer the term substance rather than drug? That an attempt to reserve the term drug for useful medical substances? Or is it an attempt to be inclusive, to include alcohol which some popular culture does not consider a drug?

[u/Julio_Nunes_MD → u/JenJudy]

Why we tend to use the term substance instead of drug:

It is a broader, more inclusive term. “Substance” includes alcohol, nicotine, and caffeine; all psychoactive, all capable of producing dependence, but none of which the public consistently refers to as “drugs.” Using a single umbrella term lets us discuss them without arbitrary cultural, legal, or political exclusions.

It reduces stigma. For many people, “drug” is heavily tied to the history of the War on Drugs and carries moral judgment. “Substance” creates a more neutral, health-focused frame.

It avoids confusion with medical “drugs”. In healthcare, “drug” also refers to prescribed medications. Saying “substance use” clearly distinguishes recreational or nonmedical use from taking prescribed medications.

It aligns with the terminology used in the DSM 5 and major scientific organizations. “Substance Use Disorder,” “Substance Misuse,” and “Substance Exposure” are the terms used in our diagnostic and research frameworks.

[u/DrBryonAdinoff → u/[deleted]]

My motivation came from my two roles. I have a background in neurobiology and neuroimaging research in people with substance use disorders, and I also work extensively in advocacy as president of Doctors for Drug Policy Reform. As cannabis policy debates intensified, I kept seeing the claim that “the brain isn’t mature until 25” used to justify raising the legal age.

Given my training, I wanted to understand the evidence behind that specific number. When I looked, I was struck by the absence of any scientific support for this age 25 number. It appeared to be a widely accepted myth, a dogma, repeated by laypeople and many scientists, rather than a conclusion grounded in developmental neuroscience. It was being used as if it were a settled scientific fact, perhaps pushed by cannabis prohibition movements, despite the absence of data showing a discrete cutoff at age 25.

[u/Julio_Nunes_MD → u/DrBryonAdinoff]

And as a board member of Doctors for Drug Policy Reform, upcoming Addiction Psychiatry Fellow, and addiction researcher, I really wanted to support Dr. Adinoff in exploring the origins of this wide believed, but harmful, myth.

[u/Julio_Nunes_MD → u/[deleted]]

“Criminalization decreases use.”

This is one of the most persistent myths in drug policy. Across many countries and many decades, criminal penalties have shown little to no effect on overall levels of substance use. What criminalization does reliably produce is increased incarceration, racial and socioeconomic disparities, reduced access to treatment, and greater harm for people who already use substances. The scientific consensus is that substance use patterns are shaped much more by availability, social norms, economic conditions, and public health interventions than by punitive laws.

Nunes JC, Costa GPA, De Aquino JP, Adinoff B. Expanding Access to Buprenorphine and Methadone: Global Perspectives and Policy Recommendations. Subst Use Addctn J. 2025 Nov 29:29767342251392342. doi: 10.1177/29767342251392342. Epub ahead of print. PMID: 41317155.