Recurring
Louis Driscoll (played by Benjamin Kimball Smith) – Alex and Ray's abrasive friend, who moves to Paradise Valley from Cincinnati in season 2. At first Alex is jealous of Louis, but they finally become friends. Alex and her gang generally find Louis annoying, with a grandiose personality, but at times he can be a very caring and well-meaning person, such as when he attempts to rescue a young child trapped beneath a cement pipe, or when he helps Alex make a friendship video for Nathan Dean in their class. Louis's father is a businessman and entrepreneur.
David "Dave" Watt (played by John Nielsen) – The seemingly dim-witted truck driver who was driving the truck that accidentally dumped the GC-161 chemical on Alex. As the only witness to the accident, Dave is often forced to serve as a partner to Vince Carter in trying to capture Alex. After seeing Alex using her powers while she was in high school, Dave keeps it a secret from Danielle to protect her as he knew what kind of horrible experiments Danielle had planned for her. In season 4, Dave reveals himself to be much more intelligent than Danielle believes, telling her that he just likes living a simple life, and serving as a whistleblower to George Mack about corruption at the plant. Alex hugs him after learning that he kept her secret to protect her, and George, in gratitude, later promises Dave a job at another chemical plant.
Scott Greene (played by Jason Strickland) – Alex's junior high school crush, an older sports jock who dates Kelly later on. Alex eventually discovers Scott's vapid nature when he steals her photos that she took while working for the school scrapbook.
Jessica (played by Jessica Alba) – Scott's first girlfriend and Alex's first school rival.
Kelly Phillips (played by Hilary Salvatore) – Scott's second girlfriend and Alex's second school rival. Kelly deviously discredits Alex at every given turn, much to Alex's dismay.
Robyn Russo (played by Natanya Ross) – One of Alex and Ray's neighborhood friends. Though she possesses a sardonic sense of humor and is fun to be around, she suffers from low self-esteem and can be very depressing, sometimes expressing grim opinions of death and nihilism. Robyn often wears black and dresses more goth as the series goes on. She has a hamster named Donald that dies, sending her into an intense grieving period. Robyn eventually discovers Alex's powers in the series finale, initially not believing Louis when he tells her.
Nicole Wilson (played by Alexis Fields) – Another of Alex and Ray's friends. An opposite personality to Robyn, has a take-charge attitude and rebellious demeanor. Nicole is often involved in social justice causes, mainly environmentalism and animal rights. In season 3's episode "The Neighbor", Danielle Atron strangely sees her younger self in Nicole's idealism and goals of making the world a better place, but admits that becoming the CEO of Paradise Valley Chemical has since made her apathetic. Nicole does not appear in the final episode of the series to discover Alex's powers.
Danielle Atron (played by Louan Gideon) – The CEO of the Paradise Valley Chemical Plant who is the main antagonist of the series. She wants to market GC-161 as a radical new weight-loss drug, and is increasingly focused on finding the GC-161 child (who she never discovers is Alex until the last two episodes) and capture them, as both a test subject and a threat to the secrecy of her plans. In season 2, Danielle's childhood is examined, revealing that she was a prodigy. When Danielle stopped speaking to her grandparents, neighbors started gossiping that she was removed from her home after she was discovered locked in the basement by her mother. Her grandmother sold the land Danielle later bought as a location to build Paradise Valley Chemical. In season 4, it's revealed in a newspaper clipping in Hunter's bedroom that Danielle had rescued several people in a fire at a rival chemical plant, but that the accident caused toxicity and genetic defects affecting Danielle and the other fire victims, after which Danielle established Paradise Valley Chemical as the main factory in town. Danielle's grandmother was played by Michael Learned in season 2's "The Secret", a Halloween-themed episode.
Carlton (played by Jason Marsden) – Carlton is Danielle's geeky, manipulative nephew and Annie Mack's scientific rival. Carlton attempts to sabotage Annie's project at a science fair in season 1. Vince initially believes Carlton to be the GC-161 child, but this turns out to be false. Carlton then loses the science fair to Annie, and is last seen crying next to his failed project.
Vincent "Vince" Carter (played by John Marzilli) – The head of security at the Paradise Valley Chemical Plant, Vince is a former Navy Seal and uses illegal tactics to protect Danielle's interests. Vince often remarks about the Federal Government, "I'm not one of their favourite guys", and is mentally unstable, although it is never made entirely clear what occurred in his past that drove him to work for Paradise Valley Chemical. He makes it his obsession to find the GC-161 child (even after he gets fired from the Plant). After being fired, he wears military garb and talks to himself. Despite often being cruel to Dave, he at times does treat Dave as possibly the only real friend he has. While trapped in an air duct in the Mack House at one point, he breaks down sobbing after Barbara says of him, "the man had no friends" (from her time working alongside him).
Oscar (animal actor) – a chimpanzee that Dave buys Vince as a Christmas present; Oscar consumes an open jelly glass of GC-161 in season 2, gaining similar powers to Alex's. In season 3, he's revealed to have been adopted by Dave, living in Dave's trailer park.
Lars Frederickson (played by Kevin Quigley) – A skilled chemist hailing from the Paradise Valley Chemical Plant's foreign branch in Vienna. He becomes Danielle Atron's chief subordinate after Vince gets fired. Lars has a shy wife named Inez, who attends an awkward dinner at the Mack household. Annie and Lars together uncover a disturbing report from the 1970s revealing that GC-161 is older than either of them initially believed, and that all the scientists on the original research project, aside from Danielle Atron, are missing or deceased. This bothers Lars, who goes to Danielle to question her, but then he decides to help her cover up the report. Lars is named after one of the members of punk rock group Rancid.
Hunter Reeves (played by Will Estes) – Hunter comes to Paradise Valley with an agenda concerning the disappearance of his father in relation to GC-161. Alex finds a shrine to Danielle in his bedroom after sneaking in, but then discovers that he's actually been investigating the plant. Alex eventually kisses him and reveals her powers to him in season 4.
Jo (played by Jennifer Manley) – Jo is a school bully who torments Alex, Ray and Robyn in several episodes throughout seasons 3–4.
Bryce Lester (played by Josh Keaton) – Annie's longtime boyfriend throughout Season 2. Bryce and Annie go mountain-climbing, and volunteer at an amateur magic show. Eventually they break up but remain friends, leaving Annie devastated, although she does get closer to her sister afterwards.
Nathan "Creeper" Dean (played by Hank Harris) – Nathan is a shy, neurodivergent boy in Alex's film class who embarrasses Alex with a bizarre video project shown to the other students and teacher.
Gloria (played by LaReine Chabut) – Gloria is Alex's boss, a donut shop owner at the local bakery "Wayne's Wigwam". In Season 4, Alex has a falling out with Gloria over the practice of using Styrofoam plates that damage the environment.
Mr. Alverado (played by J.D. Hall) – Ray's dad, who shares Ray's passion for music.
Gino Lawless (played by Frankie Como) – Gino was a security guard at Paradise Valley Chemical. He later becomes a reoccurring government agent investigating the plant. Gino's surname was chosen ironically, as he is one of the few Paradise Valley Chemical staff who has any scruples.
Elias Griffin (played by Francis X. McCarthy) – Griffin was a member of the Food and Drug Administration, who was secretly being bribed by Danielle Atron to hide the side-effects of GC-161 so that it would be approved faster. After failing a lie detector test given by Gino, Griffin is arrested. The character appears throughout season 4.
Hannah Mercury (played by guest star Charlotte Ayanna) – the most popular girl in Alex's school, who Ray has a crush on.
Chester (played by Jim Wise) – a local policeman, one of Alex's acquaintances.
Jenny (played by Francesca Marie Smith) – Jenny is an insecure younger girl who idolizes Alex, to the point of being extremely annoying and manipulative. She bullies another girl by calling her "bubblebutt", after which Alex tries to get Jenny to behave better and appreciate the friends she has.
Gordon "Scooter" Kramer (played by Corey Joshua Taylor) – Scooter is George Mack's work colleague, and a supporting character throughout seasons 3-4.
Coach Rooney (played by Glenn Morshower) – a loud sports coach with military-like behaviour; Coach Rooney appears in all seasons of the series.