If you're going to pay a hefty premium for a stock, it better have exceptional growth prospects. A company that can grow its earnings at a high rate for years, or even decades, renders the initial price paid far less important. But the risk that the expected growth fails to materialize makes some growth stocks better than others.

What growth stocks should investors consider adding to their portfolios in June? Three of our Foolish contributors have some ideas.

Tim Green: Shares of fitness wearables company Fitbit (FIT) have been beaten down since the company went public, with investors no doubt fearing that more-capable smartwatches would eventually render the company's products obsolete. But Fitbit has shown no sign of slowing down, and while heavy spending is reducing profits at the moment, the company's products remain extremely popular.

Fitbit sold 4.8 million devices during the first quarter, with revenue rising by 50% year over year. The Blaze and Alta, new products launched by the company, accounted for nearly half of Fitbit's revenue, with one million of each sold. Fitbit expects to generate between $2.5 billion and $2.6 billion of revenue this year, up about 37% from 2015.

Fitbit's success in the future is far from guaranteed. The company is extremely susceptible to disruption, and its spending has exploded in an effort to keep up its growth. During the first quarter, R&D spending more than tripled year over year, while sales and marketing costs more than doubled. Profits took a hit as a result.

With a market capitalization around $3 billion, Fitbit trades for a bit more than its expected revenue in 2016. The market is clearly pessimistic, assuming that Fitbit can't keep up its growth, and can't improve its profitability. But for investors who believe in the Fitbit story, the stock offers growth at a reasonable price.

Sean Williams: Growth-stock investors would be wise to give Ligand Pharmaceuticals (LGND 0.50%) a closer look after the stock dipped close to double digits in May.

Ligand Pharmaceuticals isn't your traditional drug developer that spends hundreds of millions on the drug-development process with the hope of bringing game-changing drugs to market. Instead, it invests in royalty assets, which allows it to use a low-overhead cost structure to reap big benefits from even a reasonably small stream of revenue. Ligand's bread and butter is Captisol, which helps improve the solubility and stability of select drugs.

During Ligand's November Investor Day Presentation, we learned that it had more than 125 fully funded programs in the works from six-dozen partners. Two of the compounds it's currently generating sales from include Novartis' (NVS 0.93%) Promacta, and Amgen's (AMGN 1.14%) multiple myeloma drug Kyprolis, which are both projected to become blockbuster drugs, with sales north of $1 billion per year. Because Ligand's technology is found in so many developing therapies, the failure of a single therapy in clinical trials isn't devastating.

Looking ahead, Ligand is forecasting total sales of between $115 million and $119 million in 2016, which would represent about 60% growth from the $71.9 million it reported in sales last year. For 2017, management is projecting sales will be north of $160 million, with adjusted EPS expected to eclipse $5. For comparison, adjusted net income in 2015 was only $3.37.

Ligand offers growth potential that could easily surpass 20% per year through the end of the decade, and it has a highly diverse number of developing assets using its technology. As such, I believe it could be an attractive growth stock to buy in June.

Brian Feroldi: One growth stock that I think deserves some attention from investors this month is Cerner (CERN), the nation's largest provider of healthcare IT. Shares have been falling during the past year and are now more than 25% off their 52-week high, which I think affords investors the chance to buy a growth stock at a discount.

Cerner's flagship product is its Millennium electronic health-record system, which helps healthcare providers of all types to better manage their back offices. Cerner's platform makes it easier for providers to store and share patient information, eliminating the need to keep paper charts, and hospital systems around the country have been racing to adopt its offerings during the past few years.

Despite being in business for nearly four decades, the company is still growing at a healthy pace. Revenue in the most-recent quarter jumped 15.3%, to $1.14 billion.

Thanks to the scalable nature of its business, the company's net income grew even faster, jumping by nearly 36%, to $150 million. Better yet, the company's backlog also increased by 12%, to $14.6 billion, which should help to ensure that Cerner's top and bottom lines continue to head in the right direction.

For the full year, Cerner's management team believes that its adjusted earnings per share will land between $2.30 and $2.40, which would be up double digits from the $2.11 that it showed last year. With the stock price down during the past year, investors can buy shares for about 24 times full-year earnings estimates, which I think is a fair price to pay for a company that should be able to grow at double-digit rates for the foreseeable future. Add in the fact that its board recently authorized another $300 million share-repurchase program, and I think this is a solid growth stock to consider right now.