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If you're anything like me, walking down the first-aid aisle in the grocery store or drugstore creates a deer in the headlights look nearly every time. The amount of over-the-counter therapeutics that consumers can buy that'll do everything from helping wounds heal faster to reducing a fever is simply incredible.

According to U.K.-based research company Visiongain, the market value for over-the-counter drugs could reach $70 billion by 2015. By comparison, the Consumer Healthcare Products Association (CHPA) pegged total OTC drug sales at just $17.4 billion in 2011. Although these reports aren't from the same research company, one thing is clear: OTC drug growth is off the charts.

Today, there are more than 700 different over-the-counter drugs you can buy in a supermarket or drugstore than would have required you to get a prescription 30 years ago – and this number is only expected to grow. OTC drugs are both convenient for consumers who don't have the ability to see a doctor every time they have an ailment, and cost-effective since they often sell for less than they did when they were branded. Plus, going to the doctor for every ailment may not be a reasonable expense for many Americans.

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Pain relievers: a mammoth market opportunity
Pain relievers are a huge market opportunity. Research by Statista of the top 10 OTC brands surmised that they combined for $1.65 billion in total U.S. sales in 2013. 

When it comes to pain relievers there are six which arguably dominate grocery and drugstore shelves:

  • Bayer
  • Aleve
  • Excedrin
  • Advil
  • Motrin
  • Tylenol

Unless you've been living under a rock for the past couple of decades you've likely seen consumer-directed advertising promoting these brand-name pain relievers on TV, online, or in a magazine or newspaper. But, surprisingly, one of these OTC pain-relievers sits at the bottom of consumers' buy list when it comes to product loyalty.

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Why brand loyalty matters
Brand Keys, a New York-based research firm which specializes in analyzing product traits and the companies behind those products, in order to determine what drives loyalty to a brand, released its 2014 Customer Loyalty Engagement Index earlier this year and ranked these six pain relievers listed above from top to bottom in terms of how loyal customers were to the product.

Overall, a market that's nearing $2 billion in the U.S. may not sound like a make-or-break opportunity for the companies behind these products or investors, but brand loyalty can extend beyond just a single product and help build trust and an emotional connection to the brand behind the product. Therefore, understanding how consumers view the OTC space could give us clues to understanding which companies could be poised to benefit from an OTC drug sale explosion.

This pain reliever finished dead-last in customer loyalty
Now that we've covered some of the important background statistics surrounding the OTC pain-reliever industry, let's get into the meat and potatoes: the company which inspires the least brand loyalty.

Before I do the great reveal, would you care to venture a guess as to which brand of the six it is without reading any further?

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If you guessed Tylenol, an OTC drug offered by Johnson & Johnson (NYSE:JNJ), then you've correctly deduced the brand consumers are least loyal to.

According to Brand Keys' assessment, Bayer's (OTC:BAYR.Y) Aleve drove the most customer loyalty, followed by Advil, Bayer, Motrin (also manufactured by J&J) and Excedrin in a tie, and then finally Tylenol. These findings would certainly appear to make sense given that Statista pegged the market share of the OTC pain reliever market for Aleve and Advil at 11.6% and 15.6%, respectively, in 2013 within the U.S. compared to just 6.4% for Tylenol (although, to be fair, Children's Tylenol performed better, at 13.2%).

Why Tylenol brings up the caboose in brand loyalty
There are a number of factors that I suspect have played a key role in reducing consumers' desire to stick with Tylenol compared to its OTC pain-relieving peers over the years.

To begin with, manufacturing quality concerns at Johnson & Johnson's subsidiary McNeil Consumer Healthcare led to the recall of millions of Tylenol bottles beginning in 2009 and extending for a number of years thereafter. As it took years for J&J to upgrade its manufacturing facility and capacity, consumers had plenty of time to try other brands, including in-store brands. Data from Euromonitor notes that the company's share of the acetaminophen market subsequently dropped from 56% in 2009 to just 24% as of 2012.

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However, it wasn't just a recall that blasted Tylenol's image. Acetaminophen products in general have come under fire by regulators over the past couple of years for their potentially damaging effects on patients' livers when not taken properly, or when combined with alcohol. The end result of investigations by the Food and Drug Administration on acetaminophen usage was that in 2011 Johnson & Johnson lowered its maximum dose from 4000 mg per day (eight pills) to 3000 mg per day (six pills) to help prevent instances of overdoses which can lead to liver damage. By comparison, Aleve's active ingredient, naproxen sodium, hasn't garnered any bad press, making it a sort of winner by default.

Another key difference between Tylenol and Aleve is ease-of-use. Aleve's draw is that over a 24-hour period a patient only needs to take two of its tablets (one every 12 hours). By comparison, a consumer may need to take up to six extra-strength Tylenols pills to achieve the same benefits over a 24-hour period. With fewer doses to remember to take, Aleve is handily trumping Tylenol when it comes to convenience.

Putting things into perspective
For Johnson & Johnson it's beginning to look more and more obvious that Tylenol's glory days as an OTC pain-relieving giant are in the rearview mirror. With recalls still fresh in consumers' minds and other choices available with fewer dosing options, I suspect not even the Tylenol name will be enough to push sales back to where they once were.

However, this is hardly a death knell for Johnson & Johnson. Although the company doesn't break out its sales of Tylenol individually, Statista estimated the brand brought in about $200 million in 2013. Whether or not this figure vacillates even 20% in each direction probably isn't going to make too much of a difference for healthcare conglomerate J&J which is expected to bring in $75 billion in revenue this year alone.

Instead, investors looking at the big picture will want to focus on Johnson & Johnson's branded pharma segment which grew 21% in the second quarter and has successfully produced more in cumulative revenue from newly introduced drugs since 2009 than any of its peers in the U.S., Europe, or Japan. Branded drugs are where J&J will find its juiciest margins, and it's where investors should be focused if they want to know whether or not J&J can head higher from here.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.