Obagi Medical Products Inc. on Monday said that Chief Executive Steven R. Carlson has resigned, effective immediately. A board member will serve as CEO until a replacement is found.

Albert F. Hummel, who has been an Obagi director since 2005, was appointed interim CEO. He is chief executive of Cobrek Pharmaceuticals Inc. in Chicago.

Carlson had been CEO and president of the Long Beach company since 2005. “The board thanks Steve Carlson for his more than five years of service, during which time the company completed its successful initial public offering, developed and introduced several new products and saw its annual sales revenues grow from $56 million to $104 million.” Chairman Albert J. Fitzgibbons said in a statement.

Despite the praise, Carlson has taken heat from Wall Street over the company’s deteriorating relationship with its founder, Dr. Zein Obagi, who sued the company in January claiming Obagi Medical had blocked efforts to expand the Beverly Hills dermatologist’s new company, ZO Skin Health.

Obagi Medical last month terminated a 2006 agreement with Dr. Obagi and said it no longer would attempt to enforce “non-compete” provisions in the contract. Obagi Medical will accelerate quarterly retainer money payments due to Dr. Obagi as a company consultant and take a $630,000 expense in the third quarter to cover the cost.

Obagi Medical shares were down 76 cents, or 6.8 percent, to $10.40 in midday trading on the Nasdaq.