If you can get your portfolio to $1 million, that can make it a whole lot easier to live off your investments and reduce how much you need to work or to retire early. To achieve that, you'll need to find quality stocks that can generate strong gains over the years.

Today, I'll look at whether healthcare stock Doximity (DOCS 1.06%) is a good growth investment to hang on to, and if it can help you become a millionaire.

The company's fundamentals are impressive

Doximity is often compared to Microsoft's LinkedIn. It is similar in the sense it is a networking platform, in this case for medical professionals. Doctors can stay on top of news, collaborate, and use a dialer app that makes it easy to connect with patients while maintaining their privacy. 

The nature of its business makes Doximity a promising investment. The company's operations have high gross margins, which can allow it to expand its profits as its operations grow. 

DOCS Gross Profit Margin (Quarterly) Chart

DOCS gross profit margin (quarterly); data by YCharts.

Without the need for significant capital, the business has also generated positive free cash flow totaling $150.8 million over the trailing 12 months. And net income of $141.1 million has been 45% of revenue ($316.6 million) during that period. 

Today, the company says that 80% of U.S. physicians use its network, suggesting that the business is popular and could see significant growth. It makes money primarily through subscriptions, which allow companies to use the site for hiring and marketing purposes. And since it is for medical professionals, that can make it more focused than LinkedIn, which allows anyone to join. That can result in better returns for advertisers in the healthcare industry.

However, that doesn't mean it's all smooth sailing ahead for Doximity.

Why Doximity faces challenges

While the business is solid right now, there are risks that investors need to consider. Microsoft is a potentially large rival since it already owns LinkedIn, and so if Doximity's business proves to be lucrative, Microsoft could be enticed to offer a similar type of service focused on healthcare. Considering Microsoft's vast resources, that poses a risk in the long term as Doximity doesn't have the moat, or competitive advantage, to prevent that from happening.

Meanwhile, Doximity's growth has barely averaged more than 12% over the past couple of years.

DOCS Revenue (QoQ Growth) Chart

DOCS revenue (QoQ growth); data by YCharts. QoQ = quarter over quarter.

Those are decent numbers, but perhaps not the type you would expect from a fast-growing business that can help make you a millionaire. Today, the stock trades at more than 50 times its earnings; that looks far too expensive and could prevent Doximity from achieving strong returns from here on out.

I wouldn't rely on Doximity's stock

Doximity's business does have growth potential, but I'm not confident that its operations are diverse enough and that it has a wide-enough moat to withstand competition. I could see it being acquired down the road, enabling you to earn a solid return on the stock, but that likely wouldn't result in the type of significant, long-term returns that are necessary to become a millionaire.

The stock could be a good buy at a lower price point. But in the long run, there is too much uncertainty for this to be a buy-and-forget investment that you can rely on for significant gains and to help build a retirement plan. Year to date, shares of Doximity are down 30%, and given its high valuation, there could be more losses ahead.