Anxious ahead of a big job interview? Worried about giving a speech? First date nerves?

The solution, some digital start-ups suggest, is a beta blocker, a type of medication that can slow heart rate and lower blood pressure — masking some of the physical symptoms of anxiety.

Typically a trip to the doctor’s office would be necessary to get a prescription, but a number of companies are now connecting patients with doctors for quick virtual visits and shipping the medication to people’s homes.

“No more ‘Shaky and Sweaty,’” one online ad promised. “Easy fast 15 minute intake.”

That worries Dr. Yvette I. Sheline, a professor of psychiatry at the University of Pennsylvania Perelman School of Medicine.

“The first question is: What is going on with this person?” Dr. Sheline said. Are they depressed in addition to anxious? Do they have chronic anxiety or is it just a temporary case of stage fright? “You don’t want to end up prescribing the wrong thing,” she added.

In addition, although beta blockers are generally considered safe, experts say they can carry unpleasant side effects and should be used with caution.

What are beta blockers?

Beta blockers such as propranolol hydrochloride have been approved by the Food and Drug Administration for chest pain, migraine prevention, involuntary tremors, abnormal heart rhythms and other uses.

Some are still prescribed for hypertension, although they’re no longer considered the preferred treatment, mainly because other medications are more effective in preventing stroke and death.

Beta blockers can ease the physical symptoms of the “fight or flight” response to stress, such as tremors, sweaty palms or a racing heart, but they are not F.D.A.-approved to treat anxiety disorders.

For decades, doctors have prescribed them for issues other than their approved uses, including for problems like stage fright. In recent years, celebrities like Robert Downey Jr. and Khloé Kardashian have said the medications helped them overcome performance anxiety.

How do they work?

When we start feeling anxious or stressed, our bodies produce adrenaline, which prepares us to respond to perceived danger. The hormone signals our heart to beat faster and narrows our blood vessels to redirect blood to important organs like the heart and lungs. Breathing quickens, and we start to sweat.

Beta blockers work by “blocking” the effects of adrenaline. They cause the heart to beat more slowly and with less force, which helps lower blood pressure.

But if you’re feeling especially anxious, “your mind is still going to race, you’re still going to ruminate and worry,” said Regine Galanti, a psychologist in Cedarhurst, N.Y., who treats people with anxiety disorders.

In other words, beta blockers are not going to address the root of your fears. “If it becomes like a weekly, ‘Oh, I’m just having a hard time in this course. I’ll just pop a beta blocker every single time.’ I would say, ‘What’s the long-term goal here?’” she added.

Patients are typically only prescribed a few pills for specific situations where they might experience performance anxiety, said Dr. Joseph Bienvenu, a professor of psychiatry at Johns Hopkins University School of Medicine. But some online companies dole out as many as 48 at a time.

Are there any side effects?

Yes. Beta blockers can make people feel dizzy. Other potential side effects include fatigue, cold hands or feet, trouble sleeping and nightmares. They can also cause stomach problems like nausea or diarrhea and, less often, difficulty breathing.

This is why some doctors tell their patients to avoid taking them for the first time on the day of a big event.

Dr. Bienvenu advises patients to initially try the medication on the weekend, or “when you don’t have anything else to do.”

“I just want people to know how it’s going to affect them,” he said.

Is it OK to take them for a potentially scary task, like a big presentation?

Possibly. But experts suggested visiting your general practitioner first.

Beta blockers may not be advised for some people with diabetes, low blood pressure or bradycardia, which is a slow heart beat — or people with asthma or another lung disease. And certain drugs, including some cholesterol and cardiovascular medications, can interact with them.

Online doctors do not have your full medical history and have not examined you in person, said Arthur Caplan, a professor of bioethics at the N.Y.U. Grossman School of Medicine.

Without a physical exam, some patients might not know that they have an underlying issue like an irregular heartbeat, he added. And they may not know who to call if they have questions after getting a prescription.

“You need to be managed on these kinds of drugs,” he said.

For those who often face anxiety-provoking tasks like public speaking, the experts said, it might be most beneficial to try breathing techniques or exposure therapy, which involves directly confronting what makes us anxious to break a pattern of fear and avoidance.

“Masking your anxiety symptoms is not going to teach you how to manage your anxiety symptoms,” Dr. Galanti said.