I (Brian Feroldi here!) know firsthand just how painful it can be to sell a stock that has lost you money. And whenever it happens I get that nagging feeling in the back of my mind that if I just hang in there, the stock will come back and I will sell then. Unfortunately, the stock market doesn't work like that; the market doesn't care how much you paid to own a stock, so it's under no obligation to move higher just because you don't want to accept a loss.

Parting ways with a stock can be tough, so it can be helpful to have a really good concrete reason to finally say goodbye. Our team of Motley Fool healthcare contributors was asked to pick a healthcare stock that we each believe might be a good candidate to say goodbye to right now. Read below why now might be a good time to kick Isis Pharmaceuticals (IONS -0.82%)MannKind (MNKD), and AbbVie (ABBV 1.26%) out of your portfolio.

Todd Campbell: Isis Pharmaceuticals is posting disappointing returns this year, but that may not mean it's the right time to toss it aside.  

So far, Isis Pharmaceuticals' shares have lost 12% of their value in 2015, and while that's significantly worse than its peers and the broader S&P 500 market, there's reason to think that better times may be coming. The company has 38 drugs in its pipeline in various stages of development, it counts some of the planet's biggest drug developers as collaborators, and its balance sheet includes $815 million in cash. 

Of the 38 drug programs under way at Isis Pharmaceuticals, five are in phase 3 trials, and that means data may be coming that could help Isis Pharmaceuticals transition into a profitable company. If all goes well, then investors will cheer -- particularly because Isis Pharmaceuticals' track record is admittedly mixed. While the company has successfully launched Kynamro as a therapy for a rare form of high cholesterol, its sales have been tepid. Also, while Kynamro successfully made its way to market, many of Isis Pharmaceuticals' other drug programs have fizzled out during studies.

Because Isis Pharmaceuticals' future is tied tightly to its clinical-stage drugs, its shares are risky enough that they might not be right for everyone to own. If you're the kind of investor that abhors biotech's pop-and-drop nature, then Isis Pharmaceuticals probably shouldn't be in your portfolio, and it might be wise to sell so it doesn't keep you up at night. However, if you're a risk-tolerant investor who owns Isis Pharmaceuticals as part of a well-diversified portfolio, then it might be worth sticking with the stock in spite of its performance this year.

Brian Feroldi: Taking a drug all the way from an initial idea to a product that is on the market and producing revenue is a long, expensive process that's fraught with hurdles. Even the best of ideas can flame out at any point, even after they've cleared all the clinical and regulatory hurdles.

While it is still too early to know for sure, I'd say the odds are quite good that MannKind's inhaled insulin Afrezza will end up as a bust. The drug has been on the market for only about 6 months now, but the early results look ugly as its marketing partner, Sanofi, has only been able to sell about $3.3 million worth of the drug during its first two quarters on the market. For a drug that supposedly holds blockbuster potential, that's a discouraging number. 

MannKind's management team offered plenty of reasons why sales out of the gate have been so slow, and they are actively working to knock down the barriers in an attempt to spark demand, but Wall Street is extremely skeptical of the company's prospects as this point -- and I think you should be, too.

MannKind has been a tough stock to own for more than a decade now as investors have patiently waited for the promise of Afrezza to finally pay off. Given the rough start for this drug, I'm skeptical that the big payday will ever come, so I'd say it's time to kick this laggard out of your portfolio and put the money in a more promising name.

George Budwell: AbbVie is a large cap biopharma stock that I've owned pretty much since the company was spun off from Abbott Laboratories in 2013. In many ways, this stock has been a great pick both in terms of its stable dividend payout and its overall return on investment. 

That said, AbbVie has been stuck in a rut in 2015, and nothing seems to be able to break it free. In the second quarter, for example, the company posted an 11.1% rise in global sales year over year, continuing its tradition of generating double-digit sales growth. Yet the stock has fallen nearly 7% year to date.

Global economic turmoil and general stock market volatility aside, AbbVie's core problem at the moment appears to be the looming patent expiration in the U.S. for its flagship anti-inflammatory drug Humira in December 2016. Humira presently makes up over 60% of the drugmaker's total revenues, so the potential introduction of a biosimilar is weighing heavily on its shares this year. 

Complicating matters, investors were hoping AbbVie's hepatitis C therapy, Viekira Pak, could help offset any drop in revenue, but this new growth product is facing its own problems competing in an increasingly crowded market. 

To management's credit, they have provided a fairly convincing outline for how they plan on protecting Humira after it loses patent protection. But the market just doesn't seem to care or to be listening right now. 

That's why I'm having a hard time seeing how this stock can push past the market's perhaps overly pessimistic view anytime soon. Therefore, AbbVie appears to be locked into a holding pattern until Humira goes off patent and the company's defense strategy proves capable of keeping disaster at bay. As such, I'm currently mulling the idea of finally relinquishing some, or maybe even all, of my shares of this healthcare laggard.