Invasion of the Body Snatchers (1978) on Netflix

The employee of the Department of Public Health, Elizabeth Driscoll, tells his friend and coworker, the field investigator Matthew Bennell, that her boyfriend Dr. Geoffrey Howell is not the same person - he is behaving differently. Matthew suggests that Elizabeth pays a visit to his friend, the renowned Dr. David Kibner. They meet him in a lecture and he tries to convince her that she has some emotional problem with Geoffrey, while Elizabeth notes that other people are having the same complaint. When Matthew's friends, Nancy and Jack Bellicec, find a clone of Jack in their medical mud business, they call Matthew and he immediately seeks out Elizabeth. He breaks in her house and finds a clone of her. The quartet discovers that people are being replaced by exact emotionless replicas using plants that get them when they sleep.