Biotech companies have used patent claims and intellectual property protection laws to restrict access of independent researchers to GM crops for research purposes. As a result, limited research has been conducted on GM foods and crops by scientists who are independent of the GM industry. Scientists whose work has raised concerns about the safety of GMOs have been attacked and discredited in orchestrated campaigns by GM crop promoters.
Most GM crops (over 75%) are engineered to tolerate applications of herbicides. Where such GM crops have been adopted, they have led to massive increases in herbicide use.
Roundup, the herbicide that over 50% of all GM crops are engineered to tolerate, is not safe or benign as has been claimed but has been found to cause malformations (birth defects), reproductive problems, DNA damage, and cancer in test animals. Human epidemiological studies have found an association between Roundup exposure and miscarriage, birth defects, neurological development problems, DNA damage, and certain types of cancer. More here.