(We) found very little evidence for the efficacy of these over-the-counter cough preparations for cough due to the common cold.

There is no clinical evidence that over–the-counter cough expectorants or suppressants actually relieve cough. There is considerable evidence that older type antihistamines help to reduce cough, so, unless there are contraindications to using these medicines, why not take something that has been proven to work?

In this case, you have overwhelming evidence of efficacy.

The efficacy is well-demonstrated. If used appropriately, it is sometimes lifesaving.

We have found no evidence of a national conspiracy to fix gasoline prices.

The best studies that we have to date would suggest there's not a lot of justification for using these medications because they haven't been shown to work.