Once a company's shares rise rapidly, investors might wonder if it's still worth investing in the stock. The answer is that it depends. Some companies' strong performances are short-lived. Others perform well because they have attractive businesses that can deliver outsized returns in the long run. Those in the second category are worth investing in even after an impressive run.

Let's look at two examples: Eli Lilly (NYSE: LLY) and Sarepta Therapeutics (NASDAQ: SRPT).

1. Eli Lilly

Eli Lilly is firing on all cylinders. The company's clinical and regulatory progress in diabetes and obesity over the past few years has led to excellent performances on the stock market.

The drugmaker's financial results are also impressive, spearheaded by tirzepatide, a therapy for diabetes and obesity that is marketed as Mounjaro and Zepbound, respectively. In the second quarter, Eli Lilly's revenue increased by 36% year over year to $11.3 billion. Mounjaro's sales were $3.1 billion, with Zepbound's coming in at $1.2 billion.

Eli Lilly raised its revenue guidance by $3 billion when it announced its second-quarter results. There have been other positive developments for the company. Most notably, Eli Lilly earned approval for Kisunla, a medicine for Alzheimer's disease. Considering the significant unmet need in this field, expect the company's financial result to get yet another boost. There are other catalysts ahead for Eli Lilly.

Tirzepatide is seeking label expansions in treating obstructive sleep apnea and in reducing the likelihood of developing type 2 diabetes in prediabetes patients. It has already aced phase 3 studies in these areas, so approvals could come within a year. Somewhere down the road, tirzepatide could seek even more expansions if it passes more mid- and late-stage trials, including in Metabolic dysfunction-associated steatohepatitis (MASH), another potentially lucrative area.

In weight loss, Eli Lilly has several exciting pipeline projects that could also make solid progress and help jolt the stock price. In short, the company has a strong lineup that will help drive substantial revenue and earnings growth and a pipeline with programs in phase 2 and 3 studies that should make consistent progress in the coming years.

Eli Lily might have crushed the market in the past five years, but there's ample upside left ahead.

2. Sarepta Therapeutics

Last year was a challenging one for Sarepta Therapeutics, a rare disease-focused biotech. Regulators delayed the accelerated approval of Elevidys, a gene therapy for Duchenne muscular dystrophy (DMD, a rare, neurodegenerative muscle disorder); biotech investors don't like such delays, even if, in this case, it was less than a month. Then, in October, Sarepta's shares fell off a cliff when Elevidys reported mixed results in a phase 3 study that the company said would support full approval.

However, Sarepta Therapeutics' shares have performed well since that drop.

To understand why, let's look a bit closer at Elevidys. Unlike Sarepta's other medicines, all of which also treat DMD, Elevidys is a one-time treatment that addresses the underlying causes of the disease. In June of 2023, the U.S. Food and Drug Administration (FDA) granted it accelerated approval for ambulatory DMD patients between the ages of four and five, meaning it would have to pass a confirmatory study to earn traditional approval.

And despite the mixed November results from Sarepta's trial, the FDA recently gave Elevidys full approval in ambulatory DMD patients with no age restrictions, but it is still under accelerated approval for non-ambulatory ones. If Elevidys can cross this final regulatory barrier and be indicated to target DMD patients without ambulatory restrictions, it would be a boost for the company. Sarepta's top line is already growing at a good clip.

In the second quarter, revenue increased 39% year over year $362.9 million. There is room for improvement with more positive developments on the Elevidys front. Further, Sarepta has over 40 pipeline programs, including other investigational DMD medicines. In January, it started screening patients for a late-stage study for a potential therapy for Limb-girdle muscular dystrophy, another rare muscle disorder.

Sarepta Therapeutics is an innovative drugmaker with several catalysts on the horizon and the potential to become a leader in the biotech industry in the long run. So, the stock likely hasn't peaked.

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Prosper Junior Bakiny has no position in any of the stocks mentioned. The Motley Fool has no position in any of the stocks mentioned. The Motley Fool has a disclosure policy.

2 High-Flying Growth Stocks With Massive Upside Potential was originally published by The Motley Fool