Innerspace

1987 sci-fi comedy starring Dennis Quaid and Martin Short.

Quaid plays Tuck Pendleton, a Navy pilot assigned to pilot an experimental submersible that is to be shrunk down and injected into a rabbit. Unfortunately, bad guys after the shrinking technology break into the lab, and one of the scientists, escaping with the syringe containing the shrunken sub with Pendleton in it, is forced to inject Pendleton into unwitting Safeway clerk Jack Putter.

Then things get weird (well, weirder). The film was directed by Joe Dante and features special effects by Rob Bottin, which might help give you an idea of what you're in for.

Not to be confused with cult classic PC game Operation: Inner Space

Tropes used in this film:
"Tuck: Okay, buddy, let me show you how I spell 'relief'!""
 * Action Survivor: Jack, to a "T."
 * Adrenaline Makeover: Jack, again. A rare male example, and in the most literal sense possible. Tuck literally stimulates Jack's adrenal gland!
 * And the Adventure Continues: At the end of the film, a newly-empowered Jack sees The Cowboy disguised as Tuck and Lydia's limo driver (with Scrimshaw and Dr. Canker hidden in the trunk, but Jack doesn't know it,) and chases after them.
 * Applied Phlebotinum: The whole plot revolves around retrieving the one-of-a-kind miniaturization/re-enlargement chips. Both projects have entire, working installations devoted to the miniaturization process, but for some reason even the villainous rivals need exactly the same chips as the government-funded laboratory.
 * Artificial Limbs / Swiss Army Appendage: The assassin Mr. Igoe is missing his right hand, and has it replaced with a system of different swappable false hands, ranging from an ordinary cosmetic hand, to one with a pointing finger that is actually a gun, to a drill-hand.
 * Even a juice dispenser.
 * In a scene where he finishes dinner with Dr. Canker, he replaces a fork attachment with... something else... that hums...
 * Big Bad: Victor Scrimshaw.
 * Chase Scene: Involving Tuck's Mustang chasing the refrigerated truck where Jack was held captive.
 * Computer Voice: The computer aboard the...
 * Cool Ship: Tuck's minisub, reminiscent of the Discovery's space pods, and armed with an amazing array of gadgets and sensors. It even recognized Jack's human physiology immediately and auto-mapped it despite having been programmed to go into a rabbit.
 * Crouching Moron Hidden Badass: Jack. Well, actually Tuck helped him a little...
 * Dare to Be Badass: Tuck gives a minor Rousing Speech to Jack when the latter is trapped in a refrigerator truck by Scrimshaw and Mr. Igoe. It works a little too well, or, at least, a little too early -- the truck is still moving!
 * The Dragon: Mr Igoe.
 * Dreaming of Things to Come: Jack's dream about the old lady with a (cigarette lighter) gun and the high prices of her groceries.
 * Drowning My Sorrows: Tuck, a washed-out Air Force pilot, was already an alcoholic before Lydia dumped him, then he got worse. Although he claims to have sobered up before the miniaturization project, it's obvious to his coworkers that he's off the wagon (and also to the audience, judging by all the bottles he keeps stashed away in odd places in his apartment).
 * Everyone Calls Him Barkeep: The Cowboy, Badass master of industrial espionage, counterfeit, smuggling, and snakeskin clothing.
 * Eye Scream: Sort of. Tuck uses an electronic transmitter implanted into the clueless Jack's optical nerve to see what's going on. The problem is, installation of said transmitter is not exactly painless to Jack...
 * Jack even describes that it feels like someone shot a hot needle through his eye. Before that, he feels like there's something in his eye because Tuck's sub lands on the nerve behind his eyeball.
 * Exact Time to Failure: Tuck has a very limited supply of oxygen, so Jack must get him (and the chips) back to the lab before it runs out.
 * Explosive Decompression: What would happen to the minisub if the cockpit were breached, which is why Tuck can't just go to the lungs to resupply his oxygen tanks.
 * Fainting: Scrimshaw's blond Mooks keeps passing out amidst too much excitement.
 * Fantastic Voyage Plot: Self-explanatory. The effects are still awesome enough to be a deep well of Squick for some viewers.
 * For Science: What the original government project was intended for. The rival lab, on the other hand, has more lucrative goals in mind.
 * Hannibal Lecture: Scrimshaw to Jack.
 * Headphones Equal Isolation: Mr. Igoe puts on his Walkman as he drives the truck Jack is imprisoned in. Naturally, he never even realizes he's involved in a Chase Scene.
 * Hearing Voices: Tuck communicates with his host via an electronic linkup in Jack's ear, and naturally Jack initially thinks he is insane when he hears Tuck's voice inside his head.
 * Heel Face Turn: Tuck's "friend" and government money man Pete Blanchard is quite the ruthless S.O.B. early in the film, willing to sacrifice Tuck's life to ensure the survival of Dr. Niles' project, but then randomly at the end turns up to personally chauffeur Jack back to Niles' lab to save Tuck.
 * Pete thought of using both Tuck and Jack to lure the rival lab.
 * Heroic Sacrifice: Scientist Ozzie Wexler dies via a gunshot to the back whilst injecting Tuck into Jack.
 * Hollywood Acid: Jack's stomach -- especially what it does to in the final battle. (Thanks a whole lot, Rob Bottin.)
 * Hot Scientist / Third Person Seductress: Margret Canker, and how.
 * Ill Boy: Jack believes he is one of this. As it happens, he's the ultimate hypochondriac, to the point he might really give himself a heart-attack by stressing out over having a heart-attack.
 * Implacable Man: Mr. Igoe redefines the trope.
 * Improbably Cool Car: Tuck's pristine red Mustang convertible.
 * Intrepid Reporter: Lydia, Tuck's girlfriend.
 * Jerk With a Heart of Gold: Tuck. Pompous and alcoholic but if you need him he can help you and give you good advices.
 * Latex Perfection: Thanks to the little guy inside you who can stimulate your facial nerves just so. (Real reason: because every Joe Dante movie needs a Transformation Sequence, that's why.)
 * Love Triangle: More or less. Jack is attracted by Lydia who still loves Tuck, having however some kind of affect towards Jack.
 * Mad Scientist: Dr. Canker. With a touch of Mad Doctor.
 * Also Dr. Niles. Dr. Canker is sort of his Distaff Counterpart.
 * Magic Feather: Jack, when he thinks Tuck is still inside him and feeding him doses of adrenaline, rescues Lydia bravely.
 * Amusingly (and a little dishearteningly), when he learns the truth, he instantly becomes a nebbish again.
 * Not really. He does have an Oh Crap, but he still knocks the mook out - and then the No Ending ending...
 * : Lydia, who keeps it from Tuck. The thing is, when he found out (in the weirdest way possible, mind you),.
 * Misapplied Phlebotinum: The minaturization process is described as "breaking an object down to its component particles to 'compile' a microscopic version of the object". The first part would be called "destructive uploading", and is actually being seriously researched both for machines and people(there are ethical concerns for people, as even if you can perfectly reconstruct the human, it's still essentially murder by perfect body disposal, but it's a secret government project doing it meaning Screw the Rules I Make Them). But if they can "compile" Tuck as a human the size of an amoeba while retaining his intelligence, then they have a computer chip that makes the NSA's best stuff as of 2012 look like an abacus. You'd need that kind of processing power to upload stuff, but that's civilization-changing technology. And they're using it, with No Plans No Prototype No Backup, on a rabbit, as a precursor to fitting people with sensory-jacking surveillance equipment. Reed Richards Is Useless.
 * Names to Run Away From Really Fast: Again, Dr. Canker.
 * No Ending: "Jack Putter to the rescue!"
 * No Plans No Prototype No Backup: The chips. Lampshaded. They're one-of-a-kind, nobody can replicate them or their technology, and nobody made backups in case they were lost or damaged.
 * Pair the Spares: Wendy and Dr Greenbush share a longing glance at the end.
 * Pint Sized Powerhouse: Scrimshaw and Dr. Canker, after.
 * Pre Mortem One Liner:

"Tuck: Who are you? What's your name?
 * Tuck's delivery makes it pretty damn sweet though, as does the score.
 * Reasonable Authority Figure: Project leader Dr. David Niles is rather likable and understanding for a gub'mint scientist.
 * He's kind of weird and borders on Mad Scientist, though.
 * Running Gag: The Cowboy - he's classified.
 * San Francisco: The main setting of the movie.
 * Second Hand Storytelling: Something must have happen between Ozzie Wexler and Dr. Canker.
 * Shout Out: Alice in Wonderland. Though why anyone would set up the miniaturization/re-enlargement process selection screen that way is anyone's guess.
 * Also, 2001: A Space Odyssey, in the aforementioned design of the pod. And the... unusual way Tuck meets  for the first time.
 * Staring Kid: There's one when Mr. Igoe shoots a scientist with his gun hand.
 * Stun Guns: Lydia tries to use one on Mr. Igoe. It backfires horribly.
 * Techno Babble: The miniaturization process in the film is depicted as breaking up a macroscale object into its component molecules to "compile" a microscopic version of that object. The loss of so much of the objects mass is presumably the reason why the administrator (Dr Niles) described the re-enlargement process as "tricky" & why two chips are used - one on the pod, one on the miniaturizer - as they can serve as a guide for exactly how to rebuild the object. So they're using a variation of Encom's scanning laser.
 * Three Amigos: Tuck, Jack, and Lydia, in a sense.
 * To Absent Friends: "We're going to make a toast to Ozzie, who saved my ass by injecting me into yours."
 * Took a Level In Badass: Jack, oh so amazingly.
 * Vanity License Plate: Igoe's BMW ("SNAPON") and Scrimshaw's Rolls-Royce ("SUB-ZRO").
 * The Voice: Tuck is this from Jack's perspective.
 * The Voiceless: Igoe never says a word in the entire film. Unless you count, "Arrrrrggggh!"
 * What Happened to The Mouse: By the end of the movie, all of the sensors Tuck implanted on Jack's body (and Mr. Igoe's damaged pod ) are still in there. Doesn't seem to bother anyone.
 * If I know anything about how the body works, Jack's body would probably get rid of the sensors. And we all know where Mr. Igoe will end up.
 * Eh, he was a piece of shit anyway.
 * What happened to the scientists who were in the miniaturization chamber with Scrimshaw and Kanker?
 * When Things Spin Science Happens: The miniaturization process at the government lab spins Tuck's minisub at absurdly high rates before breaking it down and shrinking it. It's a wonder Tuck's stomach didn't object.
 * Judging by the look on his face at the time, he probably was feeling pretty queasy; he just managed to hold it together. Until he passed out from the centrifugal force, that is.
 * Whos On First: Martin Short, Andrea Martin and Joe Flaherty.

Jack: What? (to patient #1) Are you talking to me?

Waiting Room Patient #1: No.

Tuck: I'm not out there. I'm in here.

Jack: Did you hear that?

Waiting Room Patient #2: Hear what?

Jack: You didn't hear that then?

Waiting Room Patient #2: No, I'm sorry. I didn't hear anything. Are you feeling all right?

Jack: Would I be in a doctor's office if I was feeling all right?!

Tuck: Pal, we have to talk.

Jack: No, we don't.

Waiting Room Patient #2: Don't what?

Jack: Don't have to talk.

Tuck: Yes, we do.

Jack: We do?

Waiting Room Patient #2: Do what?

Jack: Have to talk.

Waiting Room Patient #2: Not unless you want to."