Guttormson is 5-6 this season with a 3.37 ERA for the Hawks.
He was the winning pitcher in Thursday night's 5-1 win over the Seibu Lions.
The Californian, who has no major league experience, is in his third season in Japan, with the highlight being a no-hitter in 2006 when he played for the Yakult Swallows of the Central League.
This isn't the first time an athlete has run into trouble using hair-growth substances.
In 2006, NHL goalie Jose Theodore failed a drug test prior to the Olympic Games.
It was later revealed to be caused by hair-growth supplements which Theodore had been taking legally for 8 years.
While in Australia, Perth Glory midfielder Stan Lazaridis is also facing an indefinite ban while authorities attempt to rule on his failed drug test which he claimed was for hair growth treatment.