Is marijuana bad for your brain? - Anees Bahji

譯者: Lilian Chiu 審譯者: Helen Chang

In 1970,

1970 年，

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

在美國，大麻被列為 一級管制藥物：

the strictest designation possible,

這是最嚴格的分類，

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

意即，大麻完全不合法， 沒有被認可的醫療用途。

For decades, this view persisted

數十年來，這個觀點一直延續，

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

延緩了關於大麻的 機制和效應的研究。

Today, marijuana’s therapeutic benefits are widely acknowledged,

現今，大麻的治療助益 已經被廣為認可，

and some nations have legalized medical use

有些國家已將其醫療用途合法化 或正在朝向這個方向邁進。

or are moving in that direction.

But a growing recognition for marijuana’s medical value

雖然大麻的醫療價值越來越被認可， 卻仍然無法回答這個問題：

doesn’t answer the question:

is recreational marijuana use bad for your brain?

將大麻用在娛樂用途上， 對大腦會有不良影響嗎？

Marijuana acts on the body’s cannabinoid system,

大麻會影響身體的大麻素系統，

which has receptors all over the brain and body.

大麻素系統在大腦 和身體各處都有受體。

Molecules native to the body, called endocannabinoids,

內源性大麻素是一種 身體內在的分子，

also act on these receptors.

它也會影響這些受體。

We don’t totally understand the cannabinoid system,

我們尚未完全了解大麻素系統，

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

但它有一個特徵，提供了 關於其功能的重大線索。

Most neurotransmitters travel from one neuron to the next

大部分神經傳導物質會透過突觸，

through a synapse to propagate a message.

從一個神經元移到另一個 神經元，以傳播訊息。

But endocannabinoids travel in the opposite direction.

但內源性大麻素的移動方向相反。

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

當訊息從一個神經元 傳到下一個神經元時，

the receiving neuron releases endocannabinoids.

接收訊息的神經元 會釋放內源性大麻素。

Those endocannabinoids travel backward

那些內源性大麻素會反向移動， 去影響到發送訊息的神經元——

to influence the sending neuron—

essentially giving it feedback from the receiving neuron.

基本上，是給它來自 接收神經元的回饋資訊。

This leads scientists to believe that the endocannabinoid system

因此，科學家相信， 內源性大麻素系統

serves primarily to modulate other kinds of signals—

主要的功能是在調節轉換 其他類型的訊號——

amplifying some and diminishing others.

放大某些訊號，減弱某些訊號。

Feedback from endocannabinoids slows down rates of neural signaling.

來自內源性大麻素的回饋資訊

會減緩神經訊號發送的速度。

That doesn’t necessarily mean

不過，這並不表示 它會減緩行為或感知。

it slows down behavior or perception, though.

For example, slowing down a signal that inhibits smell

比如，若減緩的是 抑制嗅覺的訊號，

could actually make smells more intense.

那就會讓嗅覺更強烈。

Marijuana contains two main active compounds,

大麻的成份中有兩種 主要的活性化合物，

tetrahydrocannabinol or THC, and cannabidiol, or CBD.

四氫大麻酚（THC）

和大麻二酚（CBD）。

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

一般認為大麻對於 行為、認知、知覺

會有精神上的影響， 主要的原因就是 THC，

on behavior, cognition, and perception,

while CBD is responsible for the non-psychoactive effects.

而非精神方面的效應 則是由 CBD 造成。

Like endocannabinoids,

和內源性大麻素一樣，

THC slows down signaling by binding to cannabinoid receptors.

THC 和大麻素受體結合之後， 也會減緩訊號傳送。

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

但它是一次就和這整個 蔓延擴展的擴散系統的受體結合，

at once,

whereas endocannabinoids are released in a specific place

內源性大麻素則是 受到特定的刺激之後，

in response to a specific stimulus.

在特定的地方釋放。

This widespread activity coupled with the fact

有這種廣泛的活動， 再加上大麻素系統

that the cannabinoid system indirectly affects many other systems,

會間接影響許多其他系統，

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

這就意味著，每個人 特定的大腦化學、遺傳學，

and previous life experience

以及過去經驗會深深影響 他們對毒品的體驗。

largely determine how they experience the drug.

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

比起透過單一或少數特定路徑

來產生影響的其他毒品， 大麻更是如此。

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

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

所以，如果會造成有害影響的話， 每個人的狀況也會差異很大。

And while we don’t know how exactly how marijuana

雖然我們不確切知道大麻 如何產生出特定的有害影響，

produces specific harmful effects,

there are clear risk factors that can increase peoples’ likelihood

但很明顯有一些風險因子 會增加這些有害影響發生的機會。

of experiencing them.

The clearest risk factor is age.

最明顯的風險因子是年齡。

In people younger than 25,

比起年齡超過二十五歲的人， 二十五歲以下的人

cannabinoid receptors are more concentrated in the white matter

大麻素受器會比較集中在白質。

than in people over 25.

The white matter is involved in communication,

白質會涉及溝通、

learning, memory, and emotions.

學習、記憶、情緒。

Frequent marijuana use

經常使用大麻可能會打斷 白質神經纖維束的發展，

can disrupt the development of white matter tracts,

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

並影響到大腦產生新連結的能力。

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

這可能會傷害長期的 學習能力和問題解決能力。

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

目前，還不確定這種傷害 有多嚴重，或者是否可逆。

or whether it’s reversible.

And even among young people,

即使在年輕族群中， 更年輕的人風險更高——

the risk is higher the younger someone is—

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

比如，十五歲的風險會比 二十二歲的風險高很多。

Marijuana can also cause hallucinations or paranoid delusions.

大麻也可能造成幻覺 或者偏執的妄想。

Known as marijuana-induced psychosis,

就是一般所知 由大麻引起的精神病，

these symptoms usually subside when a person stops using marijuana.

當停止使用大麻之後， 症狀通常就會漸消失。

But in rare cases, psychosis doesn’t subside,

但，在一些罕見的案例中， 精神病不會消失，

instead unmasking a persistent psychotic disorder.

反而揭開了一種持久的精神病疾患。

A family history of psychotic disorders, like schizophrenia,

這種效應最明顯 （但非唯一）的風險因子，

就是精神病疾患的家族史， 如思覺失調症。

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 在年輕人中也比較常見，

though it’s worth noting that psychotic disorders

不過有一點也值得注意，

精神病疾患本來通常就會 在這個年齡層時浮現。

usually surface in this age range anyway.

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

在這些案例中，不確定的是， 若沒有接觸大麻，

would have appeared without marijuana use—

這些精神病會不會出現——

whether marijuana use triggers it early,

是因為使用大麻 而觸發精神病早期發作，

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

或大麻只是關鍵轉折點的催化劑， 在其他情況就不會產生影響，

or whether the reaction to marijuana is merely an indication

或對大麻的反應

只代表本來就有潛藏的疾病。

of an underlying disorder.

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

不論是哪種可能， 大麻的角色因人而異。

At any age, as with many other drugs,

不論年齡，和許多其他藥物一樣，

the brain and body

在重覆使用大麻之後， 大腦和身體對它就會比較不敏感，

become less sensitive to marijuana after repeated uses,

meaning it takes more to achieve the same effects.

意即，要達到同樣的效果， 會需要用更多的大麻。

Fortunately, unlike many other drugs,

幸運的是，不像許多其他藥物，

there’s no risk of fatal overdose from marijuana,

大麻過量並沒有致命的風險，

and even heavy use doesn’t lead to debilitating

就連大麻的重度使用者， 在停止使用之後，

or life-threatening withdrawal symptoms if use stops.

也不會變衰弱或者產生 造成生命危險的戒斷症狀。

There are more subtle forms of marijuana withdrawal, though,

不過，大麻的戒斷 有比較輕微的形式，

including sleep disturbances, irritability, and depressed mood,

包括睡眠障礙、易怒、心情憂鬱，

which pass within a few weeks of stopping use.

這些在停止使用大麻後的 幾週內就會過去了。

So is marijuana bad for your brain?

所以，大麻對你的大腦不好嗎？

It depends who you are.

那就要看你是誰了。

But while some risk factors are easy to identify,

但，雖然有些風險因子 很容易辨識出來，

others aren’t well understood—

但我們對其他風險因子 了解不多——

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

也就是說，即使你沒有 任何已知的風險因子，

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

你還是可能遇到負面的影響。