There are surely strong reasons for Gilead Sciences to be worried as a recent rating report issued by Zacks on Wednesday has downgraded GILD from a 'strong-buy' rating to a 'hold' position, thereby signaling lower credit worthiness.

Zacks stated, "We are concerned about additional pricing measures in the form of rebates and discounts which could lead to a slowdown in Harvoni sales in 2015. The anticipated continued decline in Atripla sales due to newer HIV therapies is also concerning. Meanwhile, several companies including AbbVie Inc. have launched their HCV treatments in the market".

However, Zacks did acknowledge that Gilead's first-quarter earnings were above expectations and its total revenues also increased substantially over the prior year.

Zacks added that it was impressed with the performance of Harvoni in the first quarter and was also pleased with the company's dividend and share repurchase program which would increase shareholder return.

The rating downscale had an adverse effect on the shares of Gilead Sciences that traded down 0.823% on Wednesday, hitting $115.055.

Several other firms have also reacted likewise, on Wednesday; the Analysts at Vetr set a $127.24 price target on the stock and downgraded shares of Gilead Sciences from a 'buy' rating to a 'hold' rating. Earlier on June 23, the Analysts at Argus gave the company a 'buy' rating and set a $150.00 price target on shares of Gilead Sciences.

Nonetheless, Gilead Sciences quarterly earnings data released on April 30 surpassed Thomson Reuter's consensus estimate. Gilead reported $2.94 EPS for the quarter, crossing the consensus estimate of $2.32 by $0.62. Also, the company had revenue of $7.59 billion for the quarter against the consensus estimate of $6.81 billion.