Shares of Mylan held slightly lower in afternoon trade Thursday, giving up earlier gains of more than 4 percent.
The stock climbed in morning trade after the firm announced expansion of existing cost-cutting programs for its EpiPen, a life-saving device for people with severe allergies.
In late-morning trade, Democratic presidential candidate Hillary Clinton's spokesman told MSNBC that Mylan's EpiPen discounts are "insufficient."
Mylan 5-day performance (as of intraday Thursday)
Source: FactSet
Mylan is taking "immediate action" to ensure availability of EpiPens, CEO Heather Bresch told CNBC's "Squawk Box" on Thursday.
The company has come under fire for a more than 400 percent price increase in the past decade for some customers. On Wednesday, Clinton tweeted "there's no justification for these price hikes."
The stock closed 5.4 percent lower at $43.15 a share Wednesday, down more than 11 percent for the week so far and putting it on pace for its worst week in about four months.