Common Side Effects episode 9 ending explained: What does Hildy do with Marshall?

Common Side Effects episode 9, the penultimate outing of the show, premiered on Adult Swim on March 23, 2025. Titled Cliff's Edge, the episode picks up right where last week's episode ended, with Marshall reuniting with Hildy. The story follows them as they try to regrow the blue mushroom and distribute it among the population.

Warning: Spoilers for Common Side Effects episode 9 to follow. Reader discretion is advised.

Common Side Effects episode 9 ends with a huge shock. At the end of the episode, Hildy throws Marshall off a cliff after the duo runs into a heated disagreement about what to do with the mushrooms. While Marshall suffers some heavy injuries, the episode cuts off before revealing his fate, leaving it ambiguous.

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Marshall and Hildy disagree about the mushrooms in Common Side Effects episode 9

Hildy in Common Side Effects (Image via Adult Swim)

Common Side Effects episode 9 begins with Hildy revealing that she was the one who hired Amelia to bust him out of the prison, as she was once her student. She then discusses with Marshall what to do with the mushrooms and reveals that Jarvis offered her the place, believing they could all help each other and save lives with the mushroom.

Marshall then reluctantly agrees to work with Hildy but ultimately trusts her. However, as time goes on, his fears are brought to life as it turns out that Hildy is charging people for the mushrooms and is exhausting their use. Not just that, Rusty and Jarvis are also selling the mushrooms to junkies as well so they can get high.

It all comes to a head when Marshall is confronted by a man he previously saved from a car crash by giving him a mushroom, only to discover that the cure had severe side effects. Marshall then tells Hildy that more testing needs to be done with the mushroom, but in a fit of anger, she ends up luring him to the edge of a cliff and throws him off it.

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Frances and Rick launch their own product

Frances in Common Side Effects (Image via Adult Swim)

After last week's episode, in which Jonas shut down the mushroom program at Reutical and fired Rick, Common Side Effects episode 9 sees Rick and Frances go into business together. While they aren't able to replicate the mushroom, they do come out with products inspired by it, and Frances becomes the face of the company.

However, the two do disagree a bit on how to sell the product but ultimately find common ground. This also leads Jonas to want to reconnect with Rick. In Common Side Effects episode 9, Jonas learns that he only has a few months to live and there is no cure. He then tries to seek out the mushrooms himself but fails in being able to grow them.

In a final ditch effort, he tries calling Rick to get a sample of the mushroom, but Rick won't take his calls, making him further desperate.

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Copano and Harrington go their separate ways

Copano and Harrington in the show (Image via Adult Swim)

Common Side Effects episode 9 also sees a rift between Copano and Harrington take place. After pressuring Zane into giving up Marshall's location, Harrington decides to call it in, but Copano disagrees and says that the higher brass will shut the operation down. Disagreeing with each other, the two then end up going their separate ways.

Copano then seeks out Amelia and uncovers that Marshall has been working on a medicinal mushroom. Elsewhere, Harrington takes the information to Cecily and tells her that Marshall is alive and growing mushrooms in North Carolina. Cecily then decides to call the case in and take the DEA off of it. She enlists the FBI to arrest Marshall.

At the end of the episode, Harrington can be seen joining the FBI and getting ready for the raid down in North Carolina, as they plan on stopping the mushroom business.

Fans can stream Common Side Effects episode 9 on Max.