Dr. Alien

Dr. Alien is a 1989 scifi comedy film starring Judy Landers, Billy Jacoby, and Olivia Barash. Directed by David DeCoteau, the film was also released under the titles I Was a Teenage Sex Maniac and I Was a Teenage Sex Mutant. The alternative titles explain the movies plot.

Instead of Dr. Ackerman teaching biology that day, a sexy, blond substitute teacher named Ms. Xenobia arrives and informs the class she will be teaching for the time being. All the males in the class are stunned at having such a sexy woman as a teacher, apart from Wesley. Looking for a participant in an experiment, all the males in class volunteer but Ms. Xenobia selects Wesley and asks him to attend after school has finished.Wesley goes back to the class after school, where he encounters Drax, Ms. Xenobias assistant Raymond OConnor. Ms. Xenobia arrives and explains that the experiment involves being injected with a vitamin supplement and observing Wesleys reaction. Wesley does not want to participate and Ms. Xenobia agrees, before injecting him with the supplement when his back is turned. A phalliclike stalk starts to emerge from Wesleys head as a result. Becoming sexually excited by the sight of the stalk, Ms. Xenobia proceeds to remove her lab coat, revealing a white lingerie underneath. She then has sex with Wesley who is oblivious to his surroundings with Drax recording the findings. After the experiment Wesley is sent home. ........

Source: Wikipedia