????落健生發(fā)液（Rogaine）和美國聯(lián)邦儲(chǔ)備委員會(huì)（Federal Reserve，簡稱美聯(lián)儲(chǔ)）的經(jīng)濟(jì)刺激政策有什么共同點(diǎn)？請不要往本?伯南克和艾倫?格林斯潘的發(fā)際線這個(gè)方向去考慮。想不出來了吧？答案是：副作用。

????正如您可能知道的，落健生發(fā)液最初是作為血壓藥開發(fā)的，但后來“更改用途”，因?yàn)樗写龠M(jìn)頭發(fā)生長的副作用。今天我們將討論美聯(lián)儲(chǔ)的兩大副作用——與一些主要貿(mào)易伙伴的潛在貨幣戰(zhàn)以及降低聯(lián)邦預(yù)算赤字。雖然落健生發(fā)液更為家喻戶曉，但是美聯(lián)儲(chǔ)兩大副作用要比生發(fā)液重要得多。作者沒有任何冒犯禿頭男性的意思。

????美聯(lián)儲(chǔ)的第一個(gè)副作用，即貨幣戰(zhàn)爭，表明通過降低利率來刺激經(jīng)濟(jì)這種好事可能也有弊端。由于美聯(lián)儲(chǔ)降息比大多數(shù)其他央行來得更快且幅度更大，導(dǎo)致美元兌許多主要貿(mào)易伙伴國貨幣的匯率走軟。當(dāng)然，美聯(lián)儲(chǔ)并沒有大張旗鼓地向公眾表示它樂意看到這樣的局面。但事實(shí)正是如此，因?yàn)槊涝饾u貶值會(huì)使美國的出口產(chǎn)品更便宜，而進(jìn)口自他國的產(chǎn)品變得更昂貴，這樣一來就會(huì)促進(jìn)美國本土的就業(yè)增長。

????問題是，如果所有國家都尋求本幣貶值，大家都不會(huì)得到好處。【事實(shí)上，在80年前的大蕭條（Great Depression）出現(xiàn)前，這個(gè)問題就曾一度抬頭。】而且，不僅沒有好處，相關(guān)經(jīng)濟(jì)體還會(huì)面臨廣泛的不穩(wěn)定性、恐懼和貿(mào)易戰(zhàn)爭。對于這種可能性，即使像我這樣的先天樂天派都會(huì)感到有一點(diǎn)點(diǎn)緊張。

????讀者可以從下圖看出，自2009年以來，美元兌主要貿(mào)易伙伴國貨幣的匯率已下跌超過10%。正是在國際金融危機(jī)全面爆發(fā)的2009年，美聯(lián)儲(chǔ)推出了一個(gè)又一個(gè)的計(jì)劃，以期壓低利率。盡管美元可能在2009年處于虛高水平，但它隨后的下跌對貿(mào)易產(chǎn)生了重大影響。

????What do Rogaine and the Federal Reserve's economic-stimulus policies have in common? No, it doesn't involve Ben Bernanke's or Alan Greenspan's hairlines. Give up? The answer: side effects.

????Rogaine, as you may know, was originally developed as a blood pressure medication but was "repurposed" because it had the side effect of promoting hair growth. The two Fed side effects we'll discuss today -- prospective currency wars with some major trading partners, and a reduction in the federal budget deficit -- are far less known than Rogaine's. But, with all due respect to follicularly challenged males, they're a lot more important.

????The first Fed side effect, currency wars, is an example of how something good -- stimulating our economy by lowering interest rates -- can have a downside. Cutting interest rates faster and more deeply than most other central banks has weakened the dollar against the currencies of many of our major trading partners. The Fed doesn't exactly run around telling the public that it's happy to see this happen. But that's the case, because a gradually declining dollar encourages job growth in our country by making our exports cheaper and our imports more expensive.

????The problem, which reared its head in the run-up to the Great Depression 80 years ago, is that if everyone devalues, no one benefits. Instead, you get widespread instability, fear, and trade wars. The prospect of that makes even a congenital optimist like me more than a little nervous.

????You can see from the chart below that the dollar has dropped more than 10% against the currencies of our major trading partners since 2009, when the world financial crisis was in full swing and the Fed invented one program after another to drive down interest rates. The dollar may well have been artificially high in 2009, but nevertheless, its subsequent decline has had a major impact on trade.