Nano-X Imaging (NNOX 1.75%), DermTech (DMTK -8.23%), and Viking Therapeutics (VKTX 3.73%) are healthcare growth stocks with plenty of potential, little revenue, and a boatload of risk.

Share prices of Nano-X are up more than 150% this year, DermTech is up more than 70%, and Viking's shares are up 138%. The problem I have with all three companies is that while they offer disruptive products that could cause a paradigm shift in their industries, much of that potential has already been priced into their stocks. Add in the fact that none of the companies is profitable and you have a very real potential to see these inflated share prices come back to Earth in a painful deflation.

Let's look at why owners of these three stocks might want to rethink their positions.

1. Examine Nano-X's revenue plan carefully

Nano-X's shares soared when the company received 510(k) clearance from the Food and Drug Administration (FDA) to market its Nanox-ARC multi-source X-ray system on April 28. The device differs from traditional X-rays in that it provides a digital 3D tomosynthesis with cold cathode X-ray tubes. The company's other difference is that its way of making revenue will be from a pay-per-scan business model using the company's cloud-based scanning service.

The problem I see with this is that the company will then deliver its machines, which are expensive to make, for free for use in hospitals, clinics, imaging centers, and doctor's offices. It faces a long road getting facilities to switch from using the standard X-ray machines they already use, which cost quite a bit. In other words, hospitals and imaging centers already have a lot invested in standard equipment, but they would have little incentive to use a Nanox-ARC system at a high rate.

This means Nano-X may take a long time to become profitable. In the first quarter, the company reported revenue of $2.4 million, up 33%, year over year. However, it also had a net loss of $11.8 million in the quarter, an improvement from the $21.7 million it lost in the same quarter a year ago.

Now that the company is expected to begin ramping up production for its Nanox-ARC, its costs will likely increase significantly, while its revenue will take a lot longer to climb. As of the first quarter, the company had $91 million in cash, and with its burn rate expected to climb, it will likely need more cash soon.

2. DermTech may be due for a rough patch

DermTech's Smart Stickers technology differs from the typical form of a biopsy performed by dermatologists, who cut a small piece of a suspicious mole or lesion and have it examined. The problem with the standard method is that it leaves patients feeling like pin cushions.

DermTech's Smart Stickers system uses small, easy-to-use, noninvasive adhesive patches as a melanoma biopsy. Basically, the patch absorbs skin cells, which are then sent to DermTech's lab for precise analysis. Within 72 hours, the company sends a report back to the dermatologist.

The problem for DermTech is that dermatologists have been slow to adopt its system despite its benefits. In the first quarter, the company reported revenue of $3.5 million, down 6% year over year, and a net income loss of $31.3 million compared to a loss of $30.1 million in the same period a year ago. DermTech said it had cash, as of March 31, of $108.4 million -- enough, it said, to fund operations into 2024.

DermTech has grown revenue, but the problem is its losses are growing even faster. Last year, the company reported $14.5 million in revenue, up 22.6%, but it also had an earnings-per-share (EPS) loss of $3.88, 43.2% higher than the year before. My concern for investors is that an economic pullback would make the stock seem really expensive.

3. Viking's therapies face an uphill climb

Viking Therapeutics is a clinical-stage biotech company that focuses on small-molecule solutions to metabolic disorders. My concern isn't the inherent risks that come with investing with any biotech company that doesn't have an approved therapy -- or product revenue yet -- but with the company's two lead therapies, both of which appear to be coming late to the party.

Viking's lead therapy is a weight-loss drug, VK2735, a glucagon-like peptide 1 (GLP-1) receptor agonist, which mimics the GLP-1 satiety hormone in our bodies. After a promising phase 1 trial, the drug is expected to start a phase 2 trial this year. It could serve a large (and increasing) potential patient population. However, even if approved, it will face some very popular competitor therapies, including three other GLP-1 agonists made by Novo Nordisk: Wegovy (semaglutide), Ozempic (semaglutide), and Saxenda (liraglutide).

Wegovy is approved as a weight-loss drug, and Ozempic is prescribed for diabetes but is also increasingly being prescribed off-label as a diet drug. Saxenda is the oldest of the three, approved in 2014, but requires a daily injection, whereas Ozempic and Wegovy are injected weekly. One edge VK2735 might have if approved is that Viking is working on both an injectable and an oral version of the therapy.

Viking's other main therapy candidate is VK2809, which has shown promise in treating nonalcoholic steatohepatitis (NASH), a severe form of nonalcoholic fatty liver disease (NAFLD). The good news for Viking is that there are no approved therapies yet to treat NASH, and the patient population is relatively large, affecting between 1.5% and 6.5% of adults in the United States.

The bad news is there's a strong NASH therapy candidate that could be approved before VK2809. Madrigal Pharmaceuticals drug resmetirom is on track for accelerated approval to treat NASH, with Madrigal expected to put in a new drug application (NDA) filing this quarter.

The other concern with VK2809 is whether, despite positive phase 2b trial data, it will be able to clear the relatively high safety bar for NASH drugs. Concerns about toxicity levels have doomed other therapies, such as Ocaliva from Intercept Pharmaceuticals, which was turned down by the FDA in May because of safety concerns, garnering the same fate that Genfit therapy elafibranor and Gilead drug selonsertib fell to previously.

In the first quarter, Viking reported a loss of $19.5 million, up from $16.1 million in the same period a year ago. Thanks to a recent stock sale, the company has $406 million in cash, but with its therapies in early-stage trials, it will likely have to sell more stock to fund operations down the road, further diluting the stock's value.