Two underachieving potheads, Silas and Jamal, find themselves in a peculiar situation when the ghost of Silas's recently deceased friend Ivory (Chuck Deezy) pays them a visit. After Silas uses Ivory's ashes as fertilizer for his latest marijuana crop, they discover that smoking it allows Ivory's spirit to communicate and even assist them during their college entrance exams—dubbed the "THC" (Testing for Higher Credentials), a humorous twist on the SAT and a nod to tetrahydrocannabinol.
As they take the test, Ivory feeds them answers, leading both to score perfectly. With several dubious colleges extending scholarship offers, they ultimately decide on Harvard University, thanks to the convincing Chancellor Huntley (Fred Willard), who is eager to improve minority admissions.
Upon arriving at Harvard, they encounter an eclectic group including Bart (Chris Elwood), the rowing team captain, his girlfriend Lauren (Lark Voorhies), and I Need Money (Al Shearer), alongside their quirky roommates, Jeffrey (Justin Urich) and Tuan (Trieu Tran). A meeting with Dean Carl Cain (Obba Babatundé) reveals that they must maintain a GPA of at least 2.0 to keep their scholarships.
While Jamal aims to surpass Bart on the rowing team, Silas enrolls in botany classes to hone his skills. They partake in black history courses as well, with Ivory's help ensuring that they pass all their classes effortlessly. Silas's attempts to grow closer to Lauren progress, while Jamal dates Jamie (Essence Atkins), the daughter of the U.S. Vice President (Jeffrey Jones).
As the semester unfolds, their antics escalate, resulting in pranks that provoke Bart and the Dean. After a wild Halloween party leads to valuable resources being stolen, the guys find themselves bereft of Ivory's assistance. In a desperate attempt to improve their grades, Silas embarks on an experiment for a truth serum using botanical extracts, while Jamal suggests a rather reckless plan to exhume a "smart dead guy" instead.
The midterms arrive, but both boys falter in their exams, unable to grasp Silas's rather laid-back study plan. Even when attempting Jamal's outlandish idea of digging up John Quincy Adams, they find little success. Meanwhile, Gerald, a fellow student turned stoner via Ivory's inheritance, brings back remnants of the Ivory plant, though they are diminished and ineffective.
As finals loom, despair set in. However, a reminder from Jeffrey about Silas's deadline pushes him to complete the truth serum just in time to counteract the nausea from the last leaves of Ivory's plant. Though their grades still fall short, an unexpected invitation to the prestigious Harvard Alumni party comes from Jamie, courtesy of her father's alumni status.
At the celebration, Silas seizes the moment to test his serum, leading to hilarious revelations, including Lauren's shocking discovery that a supposed artifact is actually a bong, validated by the appearance of Ivory and Benjamin Franklin himself. The uproar infuriates Dean Cain, who, in a fit of rage, tries to attack the duo with an axe but is foiled and subsequently apprehended.
In the end, the boys successfully secure their place at Harvard, while Jamal gains approval to date Jamie, and Silas wins Lauren’s affection—leaving Bart helpless in their wake.
