Common Side Effects’ Co-Creators on Their Trippy New Adult Swim Thriller

What if you discovered a mushroom that could cure anything? That’s the foundational question behind Adult Swim‘s Common Side Effects, a new series from co-creators Joe Bennett (Scavengers Reign) and Steve Hely (Veep, The Office, 30 Rock)—and the answer brings a lot of chaos into the life of Marshall, the eccentric genius who stumbles upon the miracle fungus.

With the help of Frances, his former high school lab partner—who is very reluctant to tell him she now works for the CEO of a major drug company—Marshall grabs his pet turtle and goes on the run from everyone who feels threatened by his medical breakthrough, which turns out to be a lot of deep-pocketed, well-armed, wild-eyed people. 

To learn more about the series, io9 got a chance to talk to Bennett and Hely ahead of Common Side Effects‘ February 2 debut on Adult Swim.

Cheryl Eddy, io9: One of Common Side Effects’ big themes is holding health care companies accountable—something that’s taken on new meaning in the post-Luigi Mangione era. How are you feeling about the show’s new cultural context?

Steve Hely: Well, it was a little shocking. That event was deeply upsetting, of course. But it did say that we’re touching a nerve that’s something people are thinking about and talking about, and it’s electrifying people’s imaginations and beliefs. We’re definitely thinking about something that’s on the public conscious, or subconscious, and that’s exciting—and a little scary, when it breaks into active street violence. But I guess it’s cool that we’re hitting on something that’s feeling relevant. 

io9: Marshall is a pretty unconventional hero. What informed his backstory and his appearance?

Joe Bennett: He was based on a big bag of different characters. There’s Paul Stamets, who’s a mycologist—a lot of those guys kind of in the fringe world, Terence McKenna and Richard Schultz and Wade Davis and all that stuff. But also visually and a lot of Marshall’s personality came from John Laroche from [The Orchid Thief book] and Adaptation—I really loved specifically the Chris Cooper version. It’s a guy that’s a little unhinged, a little sloppy, very confident, very smart. He would always represent himself in court. He’s kind of a badass in his own way, but just not your traditional hero, tough guy-looking character. I like that Marshall’s a pacifist. He’s got his own philosophies or ideologies that he knows are a little bit in the minority.

Hely: Thinking for himself and prepared to follow a thread as far as it’s going to take him, even if it’s going to bring him into conflict with some powerful forces.

io9: Do you think that’s why Frances takes such an interest in helping him out?

Hely: I think anybody who’s that passionate and that independent and that driven is always kind of compelling, even if it’s a little weird and frightening sometimes. And then Frances is wrestling with what her place is in this world and what she really believes. We were thinking of a character who is very human and real herself, and trying not to be poor and having enough money to live, which is hard to do. That brings her to working for this company that she’s not that sure about, and her beliefs are coming into question. That just seemed like an exciting spark for a little relationship and a story that would expand as we kept telling it.

io9: There are a lot of villains on the show—drug manufacturers, insurance companies, shadowy government operatives. Which do you think is the top of the pyramid in terms of being the absolute worst?

Hely: We always kind of thought about it like—there’s no human villain. It’s more the system. Even the [drug compamy CEO] Rick or the assassins, we always tried to show a little bit of their humanity and where they’re coming from. They’re just people who are caught in a system that’s beyond all of our control. Later on in the series, we have some dark characters who give their point of view, and we always tried to make it like, “Okay, yeah, you can kind of see it from where they’re coming from,” and to make everybody motivated in a way where they’re not just like, “Haha, I’m the evil, profit-minded villain!” They have some way of looking at the world that makes sense to them, and they feel like they’re operating from a perspective that matters. 

We talked to all kinds of people with different perspectives. We talked to a retired DEA agent and we talked to pharmaceutical people. You know, the people that work at a big pharma company can make their case that, “Yeah, it cost a lot of money because we need that money for research and development. And we charge a lot because that’s how we fund the next invention. And aren’t you happy that we have Advil and penicillin and covid vaccines and stuff?” You can see it from their point of view. We tried not to make any one person a Voldemort or whatever, but rather make them multi-dimensional.

io9: I didn’t include the DEA agents on that list of villains because you get a sense they might have their moral compasses pointing in the right direction. They’re also super quirky—why did you want to lean into them as comic relief? 

Hely: A lot of that job is, you’re sitting there waiting or staking out a place. And it just seemed to us like the people at work are often talking about everything except work and life.

Bennett: We did an early animation test before we had any actors attached to the show, and we just wanted to try to understand the [DEA agents’] relationship without any characters talking. So I animated a little bit with them dancing to Harry Belafonte, and that I think in a lot of ways helped kind of give us an idea of what they’re like. 

But yeah, to Steve’s point, we talk about this a lot when we’re sort of thinking about characters and how they’re talking to each other. If Steve and I are going on a hike, we’re probably talking about anything and everything other than the actual hike itself. There’s just a lot of time to kill. There’s a lot of topics that they just kind of throw out or whatever. And then at the end of the day, they’re real people. This is their job, but they have their own wants and needs. We just tried to make [them] more than one-dimensional characters as [much as] possible.

io9: Adult Swim seems like an unusual outlet for a show like this—it has humor and fantasy elements, and the conspiracy-thriller elements, but its themes are maybe a bit more serious than we’d associate with the platform. Why was it the right place for your show?

Hely: I think it was just going to be streaming on Max and then Adult Swim got excited about it. And we were excited, both to be part of that cool, 20- or 30-year legacy of awesome shows, I’ve loved those shows for a long time, but also, it seems cool to us that they want to, like—why can’t we expand what Adult Swim means and we’ll have a serialized show that’s taking some time and isn’t loud and crazy? The tones can be a little more subdued sometimes. It’s exciting and fun that they want to expand what Adult Swim might mean. 

io9: How much is fact and how much is fiction, when it comes to the existence of a mushroom that could cure any disease?

Hely: There is a lot we don’t know about mushrooms. Mushrooms are extremely weird, and I think we’ve barely begun to understand what all they do. There are some that can heal you or give you crazy visions, and there are some that can kill you. There are some that are delicious. So it seems not totally insane to have one that could act sort of like a stem cell therapy. I don’t think there’s anything close to that yet discovered, but it didn’t seem too insane to imagine that something like that could exist.

io9: I love the voice cast, although it didn’t have a lot of people that I immediately recognized, other than Mike Judge. Did you have certain performers in mind for the characters? 

Hely: Some of the people were people that Joe knew and had worked with in the past or people that we knew. Dave [King], who plays Marshall, he’s done a little bit of acting, but he’s not mainly an actor. We love Martha Kelly [who plays Harrington]. [Joseph Lee Anderson], who plays Copano, worked with my wife on a show called Young Rock, and we just thought he had a cool voice. And a lot of the people, we just grabbed. Some of the voices are me and Joe. What we were going for was making them sound real. To us, there’s not that much of a benefit from getting some really famous person to do your animated voice. You want whatever voice is correct for embodying the character. … All our coaching or directing was like, “do it, like, no acting.” It’s hard for pro actors, especially when they’re alone in a recording booth, to get there. But I think we were able to get to that real, stumbl-y authentic kind of feel in the voice acting. 

io9: This last one is for Joe—we were big Scavengers Reign fans at io9 and were sorry it didn’t get more seasons. How are you feeling now about where it ended, and is that a story you’d ever want to return to?

Bennett: I feel fine about it. It’s going to have a future. I’m not worried about it. I’m very grateful that we got to make [one season], and that it’s got such a cool fan base that feels like it’s growing by the day. And you know, doors will open. [They] always [have]. I feel like [they’ll] continue to do that if I just don’t dwell on the negatives. I try to put my head down and blinders on and just make things that are fun. But yes, there’s more story to tell for sure.

Common Side Effects premieres its first two episodes Sunday, February 2 at 11:30pm ET/PT on Adult Swim; thereafter, there’ll be one new episode every Sunday throughout the 10-episode run. You can also stream new episodes Mondays on Max.

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