Johnson & Johnson (NYSE:JNJ) has been one of the few top healthcare companies to post strong growth within its pharmaceutical segment this year. While most of its competitors have teetered atop the patent cliff, J&J has seen global drug sales grow by an eye-popping 21% and 18% in the past two consecutive quarters, respectively. Most importantly, the strong performance of its pharma unit has helped to offset the company's faltering medical device sales, which dropped by 5.2% year over year in the third quarter.

Olysio's impact on J&J's pharma sales 
According to management's own assessment, nearly half of this growth so far in 2014 can be attributed to a single new drug: the hepatitis C therapy Olysio. In the third quarter alone, Olysio posted revenue of $796 million, making up about 9.5% of J&J's total pharma sales during the three-month period. Breaking this down further, one drug was responsible for 62.7% of all pharma growth in the third quarter, relative to a year ago, showing its immense importance to J&J's top and bottom lines. 

Incivek's rapid decline serves as a cautionary tale
Olysio's days as a important contributor to J&J's growth story might be coming to an end, however. Earlier this month, the U.S. Food and Drug Administration approved Gilead Sciences' (NASDAQ:GILD) fixed-combo pill Harvoni, which should eliminate the need to co-prescribe the more expensive mixture of Sovaldi and Olysio off-label for hepatitis C genotype 1 patients. 

Experts thus predict that Olysio sales could fall by half next quarter, following Harvoni's commercial launch. Longer term, I think investors would be wise to recall what happened to Vertex Pharmaceuticals' (NASDAQ:VRTX) hepatitis C drug, Incivek, during the run-up to the launches of Sovaldi and Olysio. In a nutshell, after garnering blockbuster sales during its first year on the market, Incivek sales plunged by a whopping 99% only a year later. History could very well repeat itself in Olysio's case. 

What slowing Olysio sales could mean going forward
Johnson & Johnson management is certainly aware of this serious threat to its pharma segment, and it is are taking action to keep the good times rolling. For example, the company is testing Olysio in combination with other products, like Sovaldi, to try to produce a competitor to Harvoni. J&J also appears primed to continue its recent string of acquisitions in the pharma space that should soften the impact of slowing Olysio sales. Last quarter, J&J acquired both Alios BioPharma and Covagen, which seems like a prelude of things to come. 

Foolish wrap-up
Olysio's importance to J&J's growth profile rose markedly last quarter as sales of its advanced prostate cancer drug, Zytiga, started to flatten out, likely reflecting the impact of Medivation (NASDAQ:MDVN) and Astella's competing drug, Xtandi. If Olysio follows in Incivek's footsteps (at least until it gains additional approvals), J&J could see its earnings growth drop into the low single-digits.

While that might sound worrisome in the near term, J&J tends to focus on the long term with its core businesses -- a trend that has paid off handsomely for investors who have held this stock through thick and thin. Going forward, I expect earnings to drop off over the next few quarters due to Harvoni's approval, putting J&J's share price under pressure. If that happens, though, I would be willing to buy shares simply because of my faith in management's ability to identify new growth opportunities. Johnson & Johnson's history of increasing dividend payouts also isn't a bad reason to keep this top healthcare name on your watchlist in case it starts to pullback.