Drug patches that deliver measured amounts of medicine over a long period would seem like a godsend for people suffering from any number of chronic ailments, from mental illness to Parkinson’s disease. But the patches on the market so far have had mixed results, notes The Wall Street Journal’s Health Blog.

A new patch to treat the early symptoms of Parkinson’s, approved by the FDA last week, has been slow to take hold in Europe. Made by Germany’s Schwarz Pharma, the patch posted a modest $12.9 million in sales last year.

Another example, according to the Health Blog: Bristol-Myers Squibb once had high hopes for Emsam, a patch to treat major depression, but its sales have been disappointing. On the flip side, Johnson & Johnson’s Duragesic pain patch has been one of the company’s best sellers, though generic competition helped trim sales by 18 percent to $1.3 billion last year.