With all the talk about Obamacare recently, I'm beginning to get a headache, though probably not as big as the whopping migraine that members of Congress probably have.

And Merck's (NYSE:MRK) migraine drugs that block the calcitonin gene-related peptide (CGRP) receptor had such potential to treat what ails me and our government servants. That is, until side effects started popping up.

Despite good efficacy data in its phase 2 trial yesterday at the International Headache Congress in Philadelphia, Merck said it's killing its backup compound, MK-3207, because patients in the phase 1 trial experienced liver-test abnormalities after going off the drug.

The lead compound, telcagepant, also looks pretty good on the efficacy side. The drug works just as well as AstraZeneca's (NYSE:AZN) Zomig, and data presented yesterday from a phase 3 trial showed that a tablet form works as well.

More importantly, there are fewer heart problems in patients taking telcagepant than in those who take Merck's current migraine drug, Maxalt. Drugs such as Maxalt, Zomig, and GlaxoSmithKline's (NYSE:GSK) Imitrex are associated with increased heart problems, including heart attacks in some patients. With a better side-effect profile, Merck really only needs telcagepant to work as well as the current offerings to be able to compete.

Unfortunately, while the heart data looks good, telcagepant may share some issues with its little brother, MK-3207. When taken daily, the drug appears to raise liver enzyme levels in patients -- an early sign of potential liver damage. Sure, Merck will ask the Food and Drug Administration to approve it for intermittent use, but the FDA will probably be worried that patients will take it more often than prescribed.

Compounds in the same class often exhibit similar side effects, and investors (and patients!) would be wise to pay attention to them. But it's also important to remember that there's often a spectrum of side effects in each class -- Merck's Vioxx was removed from the market, but Pfizer's (NYSE:PFE) Cox-2 inhibitor Celebrex has remained on the market because the heart problems related to it are less severe.

While telcagepant's liver side effects seem less severe than MK-3207's, it's not clear whether the difference is enough to get the drug on the market. All we investors can do right now is wait, and waiting is often not the worst choice to make.

Pfizer is a recommendation of the Inside Value newsletter service. If you're interested in picking through the wreckage for possible turnaround candidates, you should have the Inside Value team on your side. Check it out for free with a 30-day trial.

Fool contributor Brian Orelli, Ph.D., doesn't own shares of any company mentioned in this article. The Fool has a disclosure policy.