Significant shortages of a dozen drugs, including several chemotherapy and cancer treatment drugs, could affect patients across Canada over the coming months.

Health Canada sent out an alert to hospitals throughout the country Thursday warning that the problem "could affect the supply of medically necessary drugs imported into Canada."

The drugs include; chemotherapy drugs Tomudex and Doxorubicin; cancer treatment drugs Velcade and Torisel; Virazole, used to combat infections in infants and the antibiotic Streptomycin.

In Thursday's statement, Health Canada said the warning was based on manufacturing problems at Ben Venue Laboratories in Bedford, Ohio, and the delay caused by efforts to fix the deficiencies.

Health Canada said it will only import "medically necessary" drugs due to the shortage – those defined as being used to prevent or treat a serious or life-threatening disease.

The warning comes as health professionals are already grappling with major drug shortages.

Hospitals in Canada, the United States, and other countries, have faced drug shortages for months. Surgeries have been cancelled, alternative therapies have had to be found by doctors and some treatments have had to be cancelled before they were completed.

Eight months in 2011, about 180 drugs have been in short supply, including a number of powerful cancer drugs.

Pharmaceutical companies have not been overly forthcoming on what is causing the supply shortage, but substandard ingredients from China and India along with manufacturing problems have been blamed.

Others, however, have said the low prices of generic drugs have lowered profit margins, lowering the incentive for pharmaceuticals to produce more drugs.