The best-performing exchange-traded fund over the past month is one that has benefited from a flurry of activity in the marijuana industry.

The ETFMG Alternative Harvest fund has gained just shy of 30 percent through Aug. 29, putting it ahead of any other non-leveraged fund. Its performance was topped only by two ETFs that offer triple the downside of gold miner stocks, which have gotten clobbered.

For the $436 million MJ fund, the outperformance has come thanks to "a veritable boom in the fund's underlying stocks," ETF.com's Lara Crigger wrote Wednesday.

In particular, big alcohol companies such as Constellation Brands, Molson Coors Brewing and Diageo have taken significant stakes in Canadian marijuana companies. In addition, Scotts Miracle-Gro in April bought Sunlight Supply, the leading U.S. hydroponics distributor.