Stocks that promise huge growth potential tend to be risky. That's why growth investing isn't for the faint of heart. However, we Fools believe investors who are picky can do very well for themselves by buying high-growth stocks early and then holding on for the long term.

So, which fast-growing companies do we think are worth the risk today? We asked a team of investors to weigh in, and they picked Albemarle (ALB 3.77%), Intercept Pharmaceuticals (ICPT), and The Trade Desk (TTD 2.42%).

Businessman fanning out hundred dollar bills in his hand.

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Lithium stock on sale

Maxx Chatsko (Albemarle): Lithium stocks have had no difficulty outperforming the broader market in recent years, but all have cratered in 2018. Shares of Albemarle have taken the biggest hit among the top three producers, falling 30% year to date. Most of that can be chalked up to general market volatility and a bearish prediction from analysts at Morgan Stanley on the future of lithium. Either way, it created a great opportunity for long-term investors.

The world's leading producer of lithium turned in a solid year of operations in 2017 carried by its lithium segment -- a recurring theme in recent years. Albemarle's lithium business grew year-over-year revenue and adjusted EBITDA 35% and 42%, respectively. The segment accounted for 42% of total revenue and 58% of total adjusted EBITDA last year. 

Management expects the good times to continue in 2018. Full-year revenue guidance calls for a range of $3.2 billion to $3.4 billion, while adjusted diluted EPS is expected to fall between $5.00 and $5.40 this year. That would represent year-over-year EPS growth of 9% to 17%.

While no long-term market prediction will nail all of the details, the growing importance of lithium-based energy storage products for both mobile and stationary applications promises to allow the global lithium market to expand for years into the future. That bodes well for Albemarle shareholders that can overlook near-term volatility, as does the company's recent quota increase in Chile, where most of its operations are based, that runs through 2043. Long story short, this lithium stock's 30% drop so far this year is a great buying opportunity.

A potentially game-changing drug in the works 

Sean Williams (Intercept Pharmaceuticals): Call it a complete homer pick since it's a holding in my own portfolio, but when I think of fast-growing businesses with tons of potential upside, I think of biotech company Intercept Pharmaceuticals.

Intercept has just one approved drug, Ocaliva, but it could be the stepping stone to billions in annual sales and a hefty profit. Currently approved to treat primary biliary cholangitis (PBC), Intercept has intentions of expanding its label to include primary sclerosing cholangitis and, most importantly, nonalcoholic steatohepatitis (NASH). There is no cure for NASH, yet it adversely impacts the livers of 2% to 5% of U.S. adults. By next decade, it'll be the leading cause of liver transplants. Being the first to market in NASH could mean well over $1 billion in annual sales.

The lure for Intercept is what it brought to the table in the phase 2 Flint study. During that study, we learned that Ocaliva reduced NAFLD Activity Score by least two points in 46% of patients, led to fibrosis improvement in 35% of patients, and led to NASH resolution in 22% of patients. Comparatively, just 21% of placebo-treated patients demonstrated a two-point decline in NAFLD Activity Score, only 19% saw an improvement in fibrosis, and a mere 13% had NASH resolution. 

This looks like a slam-dunk, so you might be wondering why isn't it being treated like a slam-dunk? Concerns over Ocaliva's safety continue to swirl. Last year, investors learned of PBC-patient deaths associated with taking Ocaliva, albeit quite a few of these unfortunate deaths were a result of incorrect prescribing by physicians, which is easily correctable with improved dosing education. What's more, none of these serious adverse events were present in the Flint trial for NASH patients.

There's also competition on the horizon, with Genfit developing a NASH compound that could be ready to hit pharmacy shelves (assuming it's successful in clinical studies) at around the same time as Intercept.

Still, after reporting $131 million in sales in 2017, Intercept could more than quintuple its sales by 2021 and begin to push toward breakeven results. Understandably, this is a risky stock given its current losses. But if Ocaliva dazzles in its two NASH trials, the growth here could be enormous.

Helping advertisers reach their mark 

Brian Feroldi (The Trade Desk): Advertising used to be a relatively straightforward process for companies that had a big budget. They'd create a marketing campaign and then blast it out to consumers across the leading marketing channels of the day (which historically meant TV, print, and radio). However, modern consumers now have dozens of ways to consume media, which is making it harder and harder for advertisers to get their message out. That's where The Trade Desk can help.

The Trade Desk is a leader in the emerging field of programmatic advertising. The idea is to use highly sophisticated software and artificial intelligence to place relevant ads to specific types of consumers on the most effective channel. By using programmatic advertising businesses can target consumers like never before and ensure that they get the highest ROI on their marketing spend.

Given the advantages, demand for programmatic advertising is exploding and the Trade Desk's financial statements are flourishing. Total sales grew 52% last year to $308 million. Better yet, net income nearly doubled to $70.4 million. Wall Street responded to the prosperity by sending the share price up 65%.

While The Trade Desk's run thus far has been impressive, there's ample reason to believe that the shift to programmatic advertising is just getting started. Wall Street projects that The Trade Desk's profits will grow around 23% annually over the next five years, which, if true, is quite high for a stock that is currently trading for around 21 times forward earnings.