The strictest designation possible, meaning it was completely illegal and had no recognized medical uses.

這是最嚴苛的分類，意即大麻完全不合法，且不被可做為醫療用途。

For decades, this view persisted and set back research on the drug's mechanisms and effects.

數十年來，這個觀點一直延續，延緩了關於大麻機制及效應的研究。

Today, marijuana's therapeutic benefits are widely acknowledged, and some nations have legalized medical use or are moving in that direction.

現今，大麻的治療助益已經被廣為認可，有些國家已將其醫療用途合法化或正朝著此方向邁進。

But a growing recognition for marijuana's medical value doesn't answer the question, "Is recreational marijuana use bad for your brain?"

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:「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, which has receptors all over the brain and body.

大麻會影響身體的大麻素系統，該系統在大腦及身體各處都有受體。

Molecules native to the body, called endocannabinoids, also act on these receptors.

內源性大麻素是一種身體內在的分子，也會影響這些受體。

We don't totally understand the cannabinoid system, but it has one feature that provides a big clue to its function.

我們尚未完全了解大麻素系統，但它有一個特徵，提供關於其功能的重大線索。

Most neurotransmitters travel from one neuron to the next, through a synapse to propagate a message.

大部分神經傳導物質會透過突觸，從一個神經元移到另一個 神經元，以傳遞訊息。

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, the receiving neuron releases endocannabinoids.

當訊息從一個神經元傳到下一個神經元時，接收訊息的神經元會釋放內源性大麻素。

Those endocannabinoids travel backward to influence the sending neuron, essentially giving it feedback from the receiving neuron.

那些內源性大麻素會反向移動，去影響發送訊息的神經元，給它來自接收神經元的回饋資訊。

This leads scientists to believe that the endocannabinoid system serves primarily to modulate other kinds of signals—amplifying some and diminishing others.

這使科學家相信，內源性大麻素系統主要的功能是在調節轉換其他類型的訊號——放大某些並減弱其他訊號。

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 it slows down behavior or perception, though.

不過，這並不表示它會減緩行為或感知。

For example, slowing down a signal that inhibits smell could actually make smells more intense.

比如，減緩抑制嗅覺的訊號，實際上會讓嗅覺更強烈。

Marijuana contains two main active compounds, tetrahydrocannabinol or THC, and cannabidiol, or CBD.

大麻的成份中有兩種主要的活性化合物，四氫大麻酚（THC）和大麻二酚（CBD）。

THC is thought to be primarily responsible for marijuana's psychoactive effects on behavior, cognition, and perception, while CBD is responsible for the non-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，而非精神方面的效應 則是由 CBD 造成。

Like endocannabinoids, THC slows down signaling by binding to cannabinoid receptors.

和內源性大麻素一樣，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 at once, whereas endocannabinoids are released in a specific place in response to a specific stimulus.

但它一次就和蔓延整個系統的受體結合，內源性大麻素則是受到特定的刺激之後，在特定的地方釋放。

This widespread activity coupled with the fact that the cannabinoid system indirectly affects many other systems means that each person's particular brain chemistry, genetics, and previous life experience largely determine how they experience the drug.

這種廣泛的活動，再加上大麻素系統，間接地影響許多其他系統，意味著，每個人特定的大腦化學、基因以及過去經驗會深深影響他們對毒品的體驗。

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

大麻比起其他的藥物有更多的影響

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

藉由單一或某些特定的途徑產生影響

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

以致這些有害效果非常的因人而異

And while we don't know how exactly how marijuana

而當我們不確切知道大麻如何

produces specific harmful effects,

產生特定有害影響

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.

藉由體驗大麻

The clearest risk factor is age.

最明顯的風險因子是年齡。

In people younger than 25, cannabinoid receptors are more concentrated

如果是低於25歲的人,大麻素受器會比超過25歲的人較集中

in the white matter than in people over 25.

在白質

The white matter is involved in communication,

白質會涉及溝通

learning, memory, and emotions.

學習,記憶和情緒

Frequent marijuana use can disrupt the development of white matter tracts,

常常使用大麻會破壞白質的發展

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 or whether it's reversible.

目前，還不確定這種傷害 有多嚴重，或者是否可逆。

And even among young people, the risk is higher the younger someone is—

即使在年輕族群中， 更年輕的人風險更高——

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 is the clearest,

家族遺傳的精神失調如精神分裂是最顯著的

though not the only, risk factor for this effect.

這種效應最明顯 （但非唯一）的風險因子，

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，那就是精神疾病

usually surface in this age range anyway.

在這個年齡層比較常見

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

在這些案例中，不確定的是，

would have appeared without marijuana use—

若沒有接觸大麻這些精神病會不會出現——

whether marijuana use triggers it early,

是否因使用大麻誘使提早發生

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

是因為使用大麻 而觸發精神病早期發作，

or whether the reaction to marijuana is merely an indication

或使用大麻後的反應僅僅是一個

of an underlying disorder.

潛在失控的跡象

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 become less sensitive to marijuana after repeated uses,

在重覆使用大麻之後， 大腦和身體對它就會比較不敏感，

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

也不會變衰弱

or life-threatening withdrawal symptoms if use stops.

或者產生造成生命危險的戒斷症狀。

There are more subtle forms of marijuana withdrawal, though,

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, others aren't well understood—

但有些危險因子很容易辨認,其他則未被完全了解

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

也就是還是有可能會體驗到負面的影響

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

即使你並沒有任何已知的危險因子