It was approved back in the 70s after there being some studies that showed it was somewhat effective against congestion. I suspect it was no better than a placebo, but once it gets over the hurdle of being shown to be safe to use it probably didn't take much to get it approved. I don't think it was ever a popular product until the government starting making pseudoephedrine, which is highly effective, hard to buy.
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It was approved back in the 70s after there being some studies that showed it was somewhat effective against congestion. I suspect it was no better than a placebo, but once it gets over the hurdle of being shown to be safe to use it probably didn't take much to get it approved. I don't think it was ever a popular product until the government starting making pseudoephedrine, which is highly effective, hard to buy.