Is marijuana bad for your brain? - Anees Bahji

翻译人员: Stella Peng 校对人员: Meng Ren

In 1970,

1970 年，大麻在美国 被归为一级管制药物：

marijuana was classified as a schedule 1 drug in the United States:

the strictest designation possible,

即最严格的管理类型，

meaning it was completely illegal and had no recognized medical uses.

意味着它完全非法， 且毫无医疗用途。

For decades, this view persisted

这种观点一直持续了几十年，

and set back research on the drug's mechanisms and effects.

阻碍了对大麻机制和效用的研究。

Today, marijuana’s therapeutic benefits are widely acknowledged,

如今，大麻的治疗功效 得到了广泛的认可，

and some nations have legalized medical use

而且一些国家已经 或正在使大麻的医用合法化。

or are moving in that direction.

But a growing recognition for marijuana’s medical value

但大麻的医疗价值被认可 并不能解答一个问题：

doesn’t answer the question:

is recreational marijuana use bad for your brain?

使用娱乐性大麻是否对大脑有害？

Marijuana acts on the body’s cannabinoid system,

大麻作用于人体的内源性大麻素系统，

which has receptors all over the brain and body.

这一系统的受体遍布大脑和人体。

Molecules native to the body, called endocannabinoids,

人体自然生产的内源性大麻素分子，

also act on these receptors.

同样也作用于那些受体。

We don’t totally understand the cannabinoid system,

我们还没有完全了解 内源性大麻素系统，

but it has one feature that provides a big clue to its function.

但它的一个特性为我们了解 其功能提供了很重要的线索。

Most neurotransmitters travel from one neuron to the next

大多数神经递质 从一个神经元移动到下一个，

through a synapse to propagate a message.

通过突触传递消息。

But endocannabinoids travel in the opposite direction.

而内源性大麻素往相反的方向移动。

When a message passes from the one neuron to the next,

当消息从一个神经元传递到下一个，

the receiving neuron releases endocannabinoids.

接收神经元释放出内源性大麻素。

Those endocannabinoids travel backward

这些内源性大麻素 往回移动至发送神经元，

to influence the sending neuron—

essentially giving it feedback from the receiving neuron.

给予其接收神经元的反馈。

This leads scientists to believe that the endocannabinoid system

这一机制使得科学家们认为

内源性大麻素系统 主要负责调控其他种类的信号，

serves primarily to modulate other kinds of signals—

amplifying some and diminishing others.

即放大信号或缩小信号。

Feedback from endocannabinoids slows down rates of neural signaling.

内源性大麻素的反馈 使得神经元信号传递速度减慢，

That doesn’t necessarily mean

但这并不意味着 行为或感知速度的减慢。

it slows down behavior or perception, though.

For example, slowing down a signal that inhibits smell

例如，减慢抑制嗅觉的信号

could actually make smells more intense.

反而使得闻到的气味更加强烈。

Marijuana contains two main active compounds,

大麻含有两种主要的活性化合物：

tetrahydrocannabinol or THC, and cannabidiol, or CBD.

四氢大麻酚（THC） 和大麻二酚（CBD）。

THC is thought to be primarily responsible for marijuana’s psychoactive effects

THC 被认为主要负责 产生大麻的精神影响，

on behavior, cognition, and perception,

包括行为、认知以及感知。

while CBD is responsible for the non-psychoactive effects.

而 CBD 负责产生非精神类影响。

Like endocannabinoids,

和内源性大麻素类似,

THC slows down signaling by binding to cannabinoid receptors.

THC 通过与大麻素受体结合 来减缓信号的传递。

But it binds to receptors all over this sprawling, diffuse system

不同的是，它会立即与遍布全身的 大麻素系统中的所有受体结合，

at once,

whereas endocannabinoids are released in a specific place

而内源性大麻素仅在特定部位产生，

in response to a specific stimulus.

对特定的刺激作出反应。

This widespread activity coupled with the fact

这种大范围的影响， 以及内源性大麻素系统

对很多其他系统的间接影响，

that the cannabinoid system indirectly affects many other systems,

means that each person’s particular brain chemistry, genetics,

意味着每个人独有的脑化学、遗传学 以及之前的生活经历，

and previous life experience

largely determine how they experience the drug.

在很大程度上 决定了他们对这种药物的体验。

That’s true much more so with marijuana than with other drugs

相较于其他只通过一种 或几种特定的途径产生作用的药物，

that produce their effects through one or a few specific pathways.

大麻更是如此。

So the harmful effects, if any, vary considerably from person to person.

因此，不良影响，如果存在的话， 非常因人而异。

And while we don’t know how exactly how marijuana

虽然我们不了解大麻究竟 怎样产生特定的不良影响，

produces specific harmful effects,

there are clear risk factors that can increase peoples’ likelihood

但我们可以明确一些 会增加不良影响概率的风险因子。

of experiencing them.

The clearest risk factor is age.

最显而易见的风险因子是年龄。

In people younger than 25,

对于小于 25 岁的人， 大麻素受体更集中于脑白质中。

cannabinoid receptors are more concentrated in the white matter

than in people over 25.

The white matter is involved in communication,

脑白质参与人的交流、 学习、记忆以及情感。

learning, memory, and emotions.

Frequent marijuana use

经常使用大麻 会扰乱脑白质神经束的发育，

can disrupt the development of white matter tracts,

and also affect the brain’s ability to grow new connections.

并且会影响大脑形成新连接的能力。

This may damage long-term learning ability and problem solving.

由此可能会破环长期的学习能力 以及解决问题的能力。

For now, it’s unclear how severe this damage can be

目前，尚不清楚这一损害的 严重程度以及是否可逆。

or whether it’s reversible.

甚至对于年轻人来说， 越年轻则风险越高。

And even among young people,

the risk is higher the younger someone is—

much higher for a 15 year old than a 22 year old, for instance.

例如，15 岁的人会比 22 岁的人风险高很多。

Marijuana can also cause hallucinations or paranoid delusions.

大麻还会引起幻觉或妄想症，

Known as marijuana-induced psychosis,

统称为大麻引起的精神病。

these symptoms usually subside when a person stops using marijuana.

这些症状通常会 随着大麻的停用而消退。

But in rare cases, psychosis doesn’t subside,

但在极少数情况下， 这些症状不会消退，

instead unmasking a persistent psychotic disorder.

意味着一种持续性的精神病。

A family history of psychotic disorders, like schizophrenia,

精神病家族病史，例如精神分裂，

是产生这一效应 最为明显的危险因子之一。

is the clearest, though not the only, risk factor for this effect.

Marijuana-induced psychosis is also more common among young adults,

大麻引起的精神病 也在年轻人中更为常见。

though it’s worth noting that psychotic disorders

尽管值得注意的是，无论如何，

usually surface in this age range anyway.

精神病通常都会在这个年龄段出现。

What’s unclear in these cases is whether the psychotic disorder

无法明确的是，若不使用大麻，

would have appeared without marijuana use—

精神病是否仍旧会产生？

whether marijuana use triggers it early,

大麻是否会促使其提前发生？

is a catalyst for a tipping point that wouldn’t have been crossed otherwise,

它是一个促使病症 越过临界点的催化剂吗？

or whether the reaction to marijuana is merely an indication

或者对大麻的反应只是 一个潜在疾病的象征？

of an underlying disorder.

In all likelihood, marijuana’s role varies from person to person.

大麻的作用很可能因人而异。

At any age, as with many other drugs,

在任何年龄，如同使用其他很多药物，

the brain and body

大脑和身体会随着大麻的重复使用 而对其敏感性降低，

become less sensitive to marijuana after repeated uses,

meaning it takes more to achieve the same effects.

这意味着需要使用更多药量 以达到相同效果。

Fortunately, unlike many other drugs,

幸运的是，不像其他很多药物，

there’s no risk of fatal overdose from marijuana,

大麻没有过量致命的风险，

and even heavy use doesn’t lead to debilitating

甚至大量使用也不会导致虚弱乏力，

or life-threatening withdrawal symptoms if use stops.

停止使用也不会产生 威胁生命的戒断症状。

There are more subtle forms of marijuana withdrawal, though,

不过，戒断大麻有着更微妙的症状，

including sleep disturbances, irritability, and depressed mood,

例如睡眠障碍，烦躁不安和情绪低落，

which pass within a few weeks of stopping use.

它们都会在停用几周内消失。

So is marijuana bad for your brain?

所以大麻对大脑有害吗？

It depends who you are.

这取决于你是谁。

But while some risk factors are easy to identify,

但尽管一些危险因子很容易被确认，

others aren’t well understood—

我们对其他危险因子还不了解。

which means there’s still some possibility of experiencing negative effects,

这意味着即使你不具有 任何已知的危险因子，

even if you don’t have any of the known risk factors.

仍有可能存在负面影响。