Even though it hasn’t had its product on the market for a week, Horizons ETF Management is one of the most successful marijuana dealers in history.

The company has seen remarkably strong interest for its Medical Marijuana Life Sciences ETF HMMJ, -1.19% , Wall Street’s first marijuana-themed exchange-traded fund, which launched last week.

The fund has traded for four sessions and has risen in each of them, including a surge of 9.9% on Monday, bringing its total rise to 17.8%.

This medical device scans your brain on marijuana

Just as impressively, the fund has seen heavy trading volume, with average daily volume of more than a million shares. To compare, there have been four other ETFs launched thus far in April, according to research firm XTF. Of those, the most popular — the Cambria Tail Risk ETF TAIL, +0.67% — has average daily volume below 5,000 shares a day. The others average daily volume under 500 shares.

The Medical Marijuana fund has amassed more than C$37.6 million ($28.2 million) in assets, according to Horizons, making it the most popular fund launched this month by that metric. It’s closest competitor is the JPMorgan Global Bond Opportunities ETF US:JPGB, which has $25.1 million in assets — as well as the backing and distribution capabilities of one of the world’s largest investment banks.

Such success for a new fund is rare. According to Morningstar, while the ETF industry regularly hits new records in terms of its size — about $3.7 trillion in global assets currently — most of that money is going to a few select funds. ETFs with under $5 million in assets make up 15.4% of the category.

See also:Here’s why the ETF graveyard is getting crowded

Don’t miss:Should you invest in an ETF that’s closing?

The Horizons fund represents something relatively rare for the modern-day ETF marketplace: a new fund that tracks an industry with heavy demand but which had no vehicle that investors can use to gain broad exposure.

The legal questions surrounding marijuana have prevented regulators from approving such a fund in the past, and even Horizons’ has a somewhat limited focus — tracking companies involved with medical marijuana bioengineering and production and avoiding ones connected to recreational use.

Another proposed fund, the Emerging AgroSphere ETF, has a similar limitation. It “will not invest in any companies that are focused on serving the nonmedical marijuana market in the United States, Canada or any other country unless and until such time as the production and sale of nonmedical marijuana becomes legal in the United States, Canada or such other country, respectively,” the firm wrote in its filing with the Securities and Exchange Commission.

Still, the marijuana industry has seen surging growth of late. Sales grew 30% in 2016, according to Arcview Market Research, and they are seen tripling in four years.The growth comes as more and more people approve of legalizing marijuana, including for recreational purposes. In 2016, roughly 60% of Americans said they favored the legalization of recreational marijuana, as the industry gained support in invalidating the war on drugs and seven states voted to legalize pot for recreational or medical use.

With the launch of the marijuana ETF, one of the few “white spaces” — an industry without a dedicated fund — left for the industry is bitcoin. Last month, the Securities and Exchange Commission rejected a proposed rule change that would’ve allowed for the creation of the first such product, saying it was unnerved by the lack of regulation in the bitcoin market.