SAN FRANCISCO >> Authorities in the United States and Europe recently staged a wide-ranging crackdown on online drug markets, taking down Wall Street Market and Valhalla, two of the largest drug markets on the so-called dark web.

Yet the desire to score drugs from the comfort of home and to make money from selling those drugs appears for many to be stronger than the fear of being arrested.

Despite enforcement actions over the last six years that led to the shutdown of about half a dozen sites — including the most recent two — there are still close to 30 illegal online markets, according to DarknetLive, a news and information site for the dark web.

This week, customers could still score 5 grams of heroin — “first hand quality no mix” — for 0.021 bitcoin (roughly $170), or a tenth of a gram of crack cocaine for 0.0017 bitcoin (roughly $14) on the market known as Berlusconi.

That means the fight against online drug sales is starting to resemble the war on drugs in the physical world: There are raids. Sites are taken down; a few people are arrested. And after a while the trade and markets pop up somewhere else.

“The instability has become sort of baked into the dark-web market experience,” said Emily Wilson, an expert on the dark web at the security firm Terbium Labs. “People don’t get quite as scared by it as they did the first few times.”

Dark web markets are viewed as one of the crucial sources of fentanyl and other synthetic opioids. These drugs are often produced in China and sent to users found on the darknet. The packages flowing from China are blamed for compounding the opioid crisis in the United States.

On Empire, one of the largest markets still online, you could have your pick of more than 26,000 drug and chemical listings, including over 2,000 opioids, shipped right to your mailbox.

Illicit online drug sales have grown in complexity and volume since the shutdown of Silk Road, the original darknet market that came online in 2011 and initially offered only a small selection of psychedelic mushrooms.

When authorities took down Silk Road in 2013 and jailed its creator, Ross Ulbricht, there was a widespread assumption that his failure and punishment would deter imitators.

But the dealers who had been selling the drugs on the market migrated to competing sites set up with a similar infrastructure, using the Tor web browser, which hides the locations of the websites and their viewers, and bitcoin, which allows for essentially anonymous payments.

A few years later, in 2017, when police took down two of the biggest successors to Silk Road, AlphaBay and Hansa market, there was five times as much traffic happening on the darknet as the Silk Road had at its peak, according to Chainalysis, a firm that analyzes bitcoin traffic.

The Canadian creator of AlphaBay, Alexandre Cazes, had been living an opulent lifestyle in Thailand for years, with three properties and four Lamborghinis, thanks to the small commission that AlphaBay collected on every transaction, prosecutors said. Cazes committed suicide shortly after his arrest, according to Thai authorities.

Governments have dedicated increasingly substantial resources to fighting darknet markets, especially as their role in the rise of synthetic opioids has become clearer.

In early 2018, the FBI created the Joint Criminal Opioid Darknet Enforcement team, or J-Code, with more than a dozen special agents and staff members. Europol has its own dedicated dark web team. And authorities everywhere have broadened their focus beyond just the administrators overseeing the markets.

During the first few months of 2019, American officials conducted an operation called SaboTor, which focused on the vendors selling drugs on the darknet. There were 61 arrests in just a few weeks. One ring, in the Los Angeles area, was said to be responsible for shipping 1,500 packages of crack, heroin and methamphetamine each month.

Richard Downing, who oversees the computer crime section of the Justice Department, said he and his colleagues have focused on techniques that create distrust on the sites by encouraging users to believe that sellers and site administrators have already been compromised and are feeding information to law enforcement.

There are some signs that these tactics have limited the growth of the markets. When authorities took down the Wall Street Market in early May it had 5,400 vendors, only one-seventh as many as AlphaBay had when it was shuttered two years earlier.

Several markets have also chosen to ban the sale of fentanyl, to make them less attractive targets for law enforcement. Berlusconi, one of the largest markets, announced that it was making this change in early May soon after Wall Street Market was shut down.

But the impact of the law enforcement activity of the last two years could be temporary.

Data from Chainalysis suggests that before the latest crackdown, overall transactions on the darknet had recovered to nearly 70% of the previous peak, right before AlphaBay went down, and were growing each month.

Downing, the Justice Department lawyer, said that for now there was a recognition, even among authorities, that darknet markets had become an enduring part of the criminal economy.

“After some years now of this cycle, it would be hard to say that it’s likely we’re going to stamp this out completely,” Downing said. “I am hopeful that our efforts to spread deterrence and mistrust are having an impact on how quickly they come back and how strongly they come back.”

In late May, Dutch police shut down a site that offered what is known as bitcoin laundering, a service that made it harder for police to track bitcoin transactions by mixing transactions together.

Shortly before that, American authorities took down a news website, known as DeepDotWeb, that lived on the traditional web, providing reviews and links to darknet sites. The absence of the site is likely to make it harder for newcomers to find their way to dark web markets.

The surviving markets, and new ones that have already popped up, have adopted measures to make them more difficult targets for authorities.

Most markets allow for payments in alternative cryptocurrencies, like Monero, which are designed to be harder to track. And DeepDotWeb already has a formidable successor in the social network and news site Dread, which is available only on the darknet.

One of the new markets that have emerged recently, Cryptonia, has promised that it has figured out many of the flaws that made previous sites vulnerable to police.

“As geeks, we believe that with the right technology, most of these problems can be solved,” the Cryptonia Team Manifesto says. “That’s why we have set out to build the perfect darknet trading platform.”

There is also some concern that sellers will move away from big markets and offer their wares directly to customers on encrypted messaging systems like Telegram, which are difficult for police to monitor.

Ian W. Gray, a dark web analyst at the security firm Flashpoint, said many new entrants appeared to have concluded that the previous takedowns were a result of mistakes or small problems rather than any fundamental flaw in their business or technology.

“Law enforcement has been very successful,” Gray said. “But people forget, or they get lazy, or they think they can do it better.”