Some allergy sufferers who previously relied on EpiPen, the emergency treatment option for anaphylaxis, recently discovered a little-known generic alternative that costs a small fraction of the brand-name version's price.

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The thing is, Adrenaclick — the generic version manufactured by Impax Laboratories — isn't new. The Food and Drug Administration (FDA) first approved the auto-injector in 1939, and the only difference between it and Mylan's EpiPen is the design of the delivery system. They both contain the rescue drug epinephrine.

Mylan came under fire last year after it was revealed that the drug company gradually hiked the price of EpiPen by 400 percent since 2007. But for those who couldn't afford the $500 product, a search for a cheaper alternative ensued. One person shared their experience finding Adrenaclick and paying only $5 for the product — which was covered by their insurance — in a viral Facebook post from September 2016, shortly after the EpiPen price hike was first reported.

And on Tuesday, a Reddit user shared a similar experience. The user allegedly ended up paying only $5 for Adrenaclick after spending $350 for EpiPen.

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The main reason Mylan has been more successful than other drug companies that produce Adrenaclick is largely the product of an effective marketing campaign for its patented device, which left many patients with the impression that it was their only option, according to The New York Times:

"EpiPen, which was approved by the Food and Drug Administration in 1987, already had good name recognition, but the market was relatively small. By 2007, it had annual sales of only about $200 million. Since then, Mylan has succeeded in turning the EpiPen into a billion-dollar-a-year product by raising prices and expanding the market through advertising, lobbying, and giveaways to schools, practices that have all come under scrutiny as anger over its high price has grown."

But EpiPen's days could be numbered, some health policy experts have predicted.

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Cigna Health Insurance, one of the nation's largest providers, recently dropped EpiPen from the list of drugs its covers and announced that in 2017 it would begin to cover Adrenaclick instead. CVS, the largest pharmacy chain in the U.S., followed up by partnering with Impax to slash the price of Adrenaclick, from $200 to $109 per pack before insurance. In contrast, EpiPen costs about $340 per pack before insurance — and that's only after the company introduced a generic version of its product in response to criticism in December.

Impax did not immediately respond to inquires about current coverage of its product in the health insurance market, but experts have advised patients to ask their physicians about their eligibility for the generic version. ATTN: also reached out to Mylan for comment but did not receive a response by the time of publication.