WASHINGTON: Counterfeit versions of the popular cancer drug Avastin obtained by European regulators contain a variety of chemicals, but not the active ingredient found in the genuine drug, according to drugmaker Roche.

The Swiss drugmaker said that an analysis of the contents of the vials picked up traces of 10 substances, ranging from starch and salt to solvent chemicals like acetone, which is used in paint thinner.

Medical experts said Tuesday the chemicals are unlikely to harm patients, provided they are not taken in large doses.

The Food and Drug Administration is investigating the source of counterfeit Avastin imported and distributed by a U.S. wholesaler to doctors here. British regulators said 41 vials of fake Avastin were shipped to the United States.