But Avonex is expensive - an eye-popping $23,000 a year. Much of that Allen pays herself, even with insurance.
"I still have a very large co-pay and deductible I need to meet to receive this medication," she said. "It doesn't make any sense to me why a drug would be so costly."
Here's why: Where traditional drugs are made from chemicals, biotechs are made from living organisms. But unlike traditional drugs, there's no federal law allowing generic versions of biotech drugs - which means there's no competition.
Congressman Henry Waxman has proposed a bill allowing the FDA to approve biotech generics.
"We want competition, because competition holds down the price of these drugs," Waxman said.
Government and insurance companies are straining under the high cost of these drugs.
But in Congress, lobbyists for the biotech industry are waging a pitched battle, arguing their drugs should be protected against generic competition for an extra 14 years.
They are lobbying Congress for what's called data exclusivity, which is basically a longer period of time when the inventor of a biotech drug can keep secret how the drug gets made.
At Biogen Idec, the company that makes Avonex, CEO Jim Mullen says it takes a billion dollars to invent a biotech drug.
"After we've spent 15 years developing these products, if we don't have some time to recoup those investments, there's just not the incentive to invest behind them," he said.
Avonex has been a blockbuster investment, with $1.7 billion in yearly sales and 130,000 patients. Mullen argues the high cost of the biotechs is worth it.
"You know, what's the value of my life, you know, is it worth the value of a Honda Accord?" he asked. "I think maybe it is."
But extra protection against competiton? Waxman calls that a money grab.
"Until they have competition, they have a monopoly and if you have a monopoly over a life saving drug, you can charge whatever price people can pay," Waxman said.
Caryn Allen is both grateful for the benefits of Avonex and incensed about the price. And that's the dilemma facing Congress as it confronts generics: how long can the country pay full price for these breakthrough treatments without breaking the health care bank.