We're well into the home stretch of 2025. August is more than halfway over. But there's still plenty of time remaining in the year -- and in this month -- to invest in stocks that hold the potential to deliver tremendous returns.

Three Motley Fool contributors think they've found fantastic growth stocks to buy in August. Here's why they picked Eli Lilly (LLY 2.73%), Summit Therapeutics (SMMT 0.91%), and Vertex Pharmaceuticals (VRTX 0.66%).

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Eli Lilly is a great buy on weakness

David Jagielski (Eli Lilly): Shares of Eli Lilly went into a tailspin earlier this month, after the company reported its latest earnings numbers. Despite news of the company generating fantastic growth due to the success of its GLP-1 drugs and plenty of more growth on the horizon, there's been a flurry of bearishness surrounding the stock this year. Shares of Eli Lilly are down around 19% since the start of the year (as of Aug. 8).

The healthcare company has grown its sales by an impressive rate of 41% through the first six months of the year, with revenue totaling more than $28 billion (which is around as much as the company reported in revenue for all of 2022).

However, it was underwhelming news around its weight loss pill, orforglipron, that appeared to provide investors with a reason to sell. The pill helped people lose close to 12% of their weight in a late-stage trial, but that was short of the 15% which analysts were hoping to see. With expectations high for Eli Lilly to be a clear market leader in the weight loss space, investors appear unwilling to accept anything outside of sheer dominance.

But buying Eli Lilly on weakness makes for an intriguing opportunity, especially if you're a long-term investor. Given its robust operations, highly successful GLP-1 drugs Mounjaro and Zepbound, and loads more products in development, I firmly believe this is going to be the first healthcare stock to hit a market cap of $1 trillion in the future. Entering this week, its market value was around $560 billion; this is a stock that could have tremendous runway.

Although the recent news around orforglipron may be disappointing, Eli Lilly's business still looks incredible, and buying the pharma stock right now could make for a fantastic opportunity in the long run.

An up-and-coming drugmaker that's about to hit its stride

Keith Speights (Summit Therapeutics): Unlike Eli Lilly, Summit Therapeutics doesn't generate billions of dollars in revenue. It doesn't even have an approved product on the market. However, I think you can stick a bold "yet" at the end of both of those previous statements. Summit is an up-and-coming drugmaker that's about to hit its stride, in my view.

What's behind my optimistic outlook? Less than three months ago, Summit announced positive top-line results from its first global phase 3 clinical study evaluating ivonescimab in combination with chemotherapy as a second-line treatment for non-small cell lung cancer (NSCLC). The combo therapy reduced the risk of disease progression or death by a whopping 48% compared to chemotherapy alone.

Based on the results of this clinical trial, Summit plans to file a Biologics License Application (BLA) to the U.S. Food and Drug Administration (FDA) for approval of ivonescimab plus chemotherapy as a second-line NSCLC treatment. There's no guarantee of FDA approval. However, the fact that there aren't any current FDA-approved therapies that have demonstrated a statistically significant overall survival benefit in this indication gives investors more reason to hope for success.

Should Summit win this FDA approval, though, it could be only the tip of the iceberg. The company is also conducting phase 3 trials evaluating ivonesimab with chemotherapy as a first-line NSCLC treatment and as a monotherapy in treating metastatic NSCLC patients with high PD-L1 expression. Should these studies go well (and I suspect they will), I predict that Summit could earn a spot among the greatest cancer-treating stocks of the 21st century.

Why you should buy the dip on this top growth stock

Prosper Junior Bakiny (Vertex Pharmaceuticals): It's been a challenging year for Vertex Pharmaceuticals, a leading biotech company. The drugmaker has encountered several issues, and most recently, its shares plummeted following a clinical setback related to VX-993, an investigational therapy for acute pain. VX-993 failed to meet its primary endpoint in a phase 2 clinical trial.

Vertex's shares are down 2% this year, while the S&P 500 is up 8%. For investors focused on the long game, now might be a great time to buy. Vertex Pharmaceuticals delivers consistent revenue and earnings, and has an expanding product lineup, a deep pipeline, and a proven culture of innovation.

In the second quarter, the company's revenue jumped by 12% year over year -- a strong performance for a biotech giant -- to $2.96 billion.

The company's long-standing cystic fibrosis franchise is still performing well. That should continue long enough for Vertex's newer products, including Casgevy, which treats a pair of rare blood diseases, and Journavx for acute pain, to start making meaningful contributions to its top line. Both could hit blockbuster status eventually.

And by then, Vertex should be able to launch even newer medicines. The company's investigational therapy for type 1 diabetes, zimislecel, is performing well in clinical trials and could receive approval within the next two years.

Vertex Pharmaceuticals should continue to innovate long after, given the several products across its late-stage and mid-stage pipeline. All these factors make Vertex's prospects attractive. The company's shares might be down right now, but at current levels, they could deliver superior returns over the next five years. That's what makes the stock so attractive right now.