It has been under commercial cultivation since 1996 in the US and several other countries, and in India since March 2002.
In every country, including India, Bt cotton was subjected to rigorous bio-safety tests for 7-10 years to prove its safety to non-target beneficial organisms (like animals including mammals, birds, fish, earthworms, honey bees, parasitoids, and predators) and the environment before it was approved for commercial cultivation.
In spite of it, the safety of Bt cotton has been questioned by certain NGOs and individuals right from the beginning and it is continuing even now.
One of the most widely publicised allegations has been that the Bt which is incorporated in Bt cotton produces a toxin that is poisonous to humans, animals, other organisms, and the environment and that if cattle or goats graze on such cotton plants, their health would be affected or even die and that their milk is hazardous.
All this has created a scare among people. Otherwise, it makes no sense.
Similarly, Bt protein in a Bt cotton plant will affect only the bollworms, not any other organisms or the plant.
Since its introduction in 1996, the global area under Bt cotton has steadily increased and, as of 2018, reached 24.8 million hectares (including 11.6 m ha in India) in about 14 countries that include the US, Brazil, Argentina, China, Australia, and India as the major growers.
The benefits from Bt cotton in India included an increase in yield from 31 percent to 67 percent owing to effective control of bollworms, decrease in chemical insecticide use from 25 percent to 55 percent, net profit to farmers from ₹7,800 to ₹30,000/ha, and, moreover, India turned from an importer to an exporter of cotton.
In spite of such extensive cultivation, Bt cotton has not caused any scientifically validated ill-effects on humans, animals, other non-target organisms, or the environment anywhere in the world.