Scanners III: The Takeover (1992) on Netflix

A young female scanner turns from a sweet young thing into a murderous, power-crazed villain after she takes an experimental drug developed by her father. Her brother, who is also a scanner, is the only one powerful enough to stop her.

A young female scanner turns from a sweet young thing into a murderous, power-crazed villain after she takes an experimental drug developed by her father. Her brother, who is also a scanner, is the only one powerful enough to stop her.

—Anonymous

During the Christmas party in her apartment, Joyce Stone welcomes the stepbrothers Helena Monet and Alex Monet, who is her boyfriend. Alex's best friend asks him to demonstrate his abilities of scanner and during his demonstration, Alex is distracted by a guest and accidentally kills his friend. Alex is considered non-guilty but decides to travel to a monastery in Thailand to learn to control his powers. Two years later, Joyce and Helena are attacked by a gang in an alley and Helena activates her ability of scanner to save them. She has a severe migraine associated to the sound of voices and her stepfather Elton Monet shows an experimental EPH-3 patch that he is developing in his company to be used in scanners. Helena offers to be the guinea pig, but he does not accept the offer since he is still studying the side effects. During the night, Helena opens his wallet and secretly uses the EPH-3. Immediately her migraine disappears and she feels good; however her personality changes to an evil person. She humiliates her boss Mark Dragon, who is the owner of the TV network where she works, and later she destroys him to assume the control of the television; she kills Elton to assume the control of his company and research; she kills Dr. Baumann, who conducted painful experiments on her when she was a teenager. Meanwhile Alex's lawyer and friend Michael travels to Thailand to warn Alex about the changes in Helena but he is murdered by a scanner sent by Helena to follow him. The Monk gives a final training to Alex and he returns home. Will Alex succeed to control Helena?

—Claudio Carvalho, Rio de Janeiro, Brazil