Organic Chemistry vs. Biochemistry: Which Do PA Schools Actually Require-
The four tiers of program requirements, the admissions-director quotes that settle the question, and how to decide which course (or both) to take
There is no single answer to ‘organic chemistry vs. biochemistry for PA school.’ The right answer depends on which programs you’re applying to, and CASPA programs vary more on this question than on almost any other prerequisite. Some programs require both. Some accept either. Some require Organic only. A growing number require Biochemistry only. Picking the wrong course — or only one course when two are required — sends applicants back to a registrar’s office to enroll in another semester of chemistry.
This article is decision content. By the end, you’ll know which of four requirement tiers each of your target programs falls into, which course (or both) to take, and how to sequence your remaining chemistry coursework efficiently. Both CHEM 251 Organic Chemistry I and CHEM 330 Biochemistry I are available as self-paced 3-credit courses at PrereqCourses.com through Upper Iowa University — but which one (or both) is the right enrollment depends on your target programs.
| AT A GLANCE• CASPA programs fall into roughly four tiers on the Orgo vs. Biochem question• Tier 1: Biochemistry only required (~30% of programs) — Orgo not required at all• Tier 2: Either Orgo OR Biochem accepted as a single course (~25% of programs)• Tier 3: Both Organic Chemistry I AND Biochemistry required separately (~35% of programs)• Tier 4: Organic Chemistry only required, sometimes 2 semesters (~10% of programs)• Substitution between the two is rarely accepted — Duke, Case Western, and others explicitly refuse |
PA programs developed their chemistry prerequisite lists independently over decades, and the result is a patchwork. The trajectory across the field over the past decade has been toward Biochemistry and away from a pure Organic Chemistry requirement — because biochemistry is more clinically relevant to PA practice — but every program made the transition (or didn’t) on its own timeline. The result is the four-tier landscape applicants face today.
The cleanest way to settle which tier each of your target programs falls into is to read their admissions page language carefully. The phrases to look for:
Programs publish their prerequisite language for a reason. When in doubt, the admissions office will answer questions directly — and several have answered the orgo-vs-biochem question explicitly in public Q&As we’ll reference below.
The growing tier. These programs require Biochemistry as a separate prerequisite but do not require Organic Chemistry at all. The trend over the past decade has been toward this position because Biochemistry covers the clinically relevant material (enzyme function, metabolism, drug action mechanisms) more directly than Organic Chemistry does.
Examples include ECU’s PA program (Biochemistry will be a required prerequisite beginning with the 2026–2027 admissions cycle, with Organic Chemistry listed only as a prerequisite to the Biochem course rather than as a PA prereq itself), and many newer programs that built their requirements around current clinical curricula.
| TIER 1 PATH: BIOCHEMISTRY ONLYTake CHEM 330 Biochemistry I. Most PA programs that require Biochem assume an Organic Chemistry foundation as a prerequisite to the Biochem course itself, which means you’ll likely still need CHEM 251 Organic Chemistry I as a prerequisite to enroll in CHEM 330 — but Organic Chem itself will not appear as a required line on your CASPA prereq checklist for Tier 1 programs. |
Tier 2 programs accept either Organic Chemistry I or Biochemistry as a single course satisfying the requirement. You don’t need both. You can pick whichever fits your transcript, your timeline, or your interest.
| DIRECT FROM ADMISSIONSPenn State College of Medicine PA admissions: “As for OChem vs. Biochem — it absolutely is your choice — we require either — or…not both.” This is the cleanest Tier 2 position you’ll find in the public record. When a program offers this flexibility, take the course you’re most likely to do well in — your grade matters more than which course you pick. |
If a program lets you choose, three considerations help:
| TIER 2 PATH: PICK ONETake either CHEM 251 Organic Chemistry I or CHEM 330 Biochemistry I. For most career-changers, Biochem is the higher-value choice — it’s more clinically relevant and it clears Tier 1 and Tier 2 programs simultaneously. For applicants who’ve already taken Organic and want to avoid extending the prerequisite chain, taking Organic alone for Tier 2 satisfies the requirement. |
Tier 3 is the strictest and increasingly common tier. These programs require both Organic Chemistry I and Biochemistry as separate, named prerequisites. There’s no choice between them; both must appear on your transcript with letter grades.
CUNY School of Medicine’s PA program updated its requirements for the 2026–2027 cycle to require Organic Chemistry I with lab AND Biochemistry — and to explicitly state that Organic Chemistry I & II will no longer substitute for General Chemistry I & II. The change separated what had been a flexible chemistry requirement into a strict three-course chemistry stack: General Chem I & II, Organic Chem I, and Biochemistry.
| DIRECT FROM ADMISSIONSCase Western Reserve University PA admissions: “We do accept either undergraduate or graduate level courses for biochem and organic but they must be separate courses and they must be specific to biochem and organic, not overview courses that combine lots of different topics.” Case Western’s published requirements echo this: “Applicants must take 1 organic chemistry course with lab and 1 biochemistry course.” Combined organic-biochemistry courses (sometimes titled ‘Bio-Organic Chemistry’) do not satisfy either requirement at Case Western. |
Temple’s Lewis Katz School of Medicine PA program requires General Biology I & II, General Chemistry I & II, Organic Chemistry, Biochemistry, and Human Anatomy & Physiology — Organic and Biochem listed separately. Albany Medical College’s PA program requires both Organic Chemistry (CHE 301) or Biochemistry (CHE 451) at the program level, but most applicants take both to maximize coverage. Programs at the more academically intensive end of the CASPA spectrum tend to cluster in Tier 3.
| TIER 3 PATH: BOTH COURSESTake both CHEM 251 Organic Chemistry I and CHEM 330 Biochemistry I. Sequence them in order — CHEM 251 first, since it’s the prerequisite to CHEM 330. Plan 16–24 weeks for the pair at a steady self-paced rate. The combined cost ($1,350 for both at PrereqCourses) is dramatically lower than the state university or post-bacc equivalent (often $4,000–$6,000+). |
Tier 4 is the smallest and shrinking tier. These programs require Organic Chemistry (sometimes one semester, sometimes both Organic I and II) but do not require Biochemistry at all. This was the dominant model 15 years ago; it’s a minority position now.
| DIRECT FROM ADMISSIONSDuke University PA admissions: “We are not able to substitute Biochem for Organic Chem.” If a Tier 4 program asks for Organic Chemistry specifically, Biochemistry will not be accepted as a substitute regardless of its clinical relevance. The reverse is also true at Tier 1 programs that ask specifically for Biochemistry. Substitutions across the orgo/biochem boundary are rarely accepted by either tier. |
| TIER 4 PATH: ORGANIC CHEMISTRYTake CHEM 251 Organic Chemistry I. If your target programs require two semesters of Organic, add CHEM 252 Organic Chemistry II. Verify each program’s specific requirement — single-semester Orgo is more common in the Tier 4 PA landscape than two-semester sequences. |
Most applicants apply to 8–15 PA programs, and their target list often spans multiple tiers. The practical question becomes: given a mixed target list, what’s the most efficient course set to take?
Start at each target program’s official admissions page (not at CASPA’s program directory, which can lag the program’s own website by months). Find the chemistry prerequisite language. Categorize each program into one of the four tiers.
Make a simple table: program name, chemistry tier, notes. Patterns will emerge quickly. Most applicants find their target list clusters into two adjacent tiers (Tier 2 and Tier 3, or Tier 1 and Tier 2).
Use the decision logic below:
| Your Tier Mix | Most Efficient Course Strategy | Why |
|---|---|---|
| All Tier 1 (Biochem only) | CHEM 330 Biochemistry I | Biochem alone clears all programs |
| All Tier 2 (Either/or) | CHEM 330 (preferred) OR CHEM 251 | Pick the one you’ll grade strongest in |
| All Tier 3 (Both required) | CHEM 251 + CHEM 330 | Both required as separate courses |
| All Tier 4 (Organic only) | CHEM 251 (+ CHEM 252 if required) | Biochem not accepted as substitute |
| Mix of Tier 1 + Tier 2 | CHEM 330 alone | Biochem clears Tier 1, and Tier 2 accepts Biochem as the ‘either’ option |
| Mix of Tier 2 + Tier 3 | CHEM 251 + CHEM 330 | Tier 3 requires both; Tier 2 accepts either; Tier 3 dictates the strategy |
| Mix of Tier 3 + Tier 4 | CHEM 251 + CHEM 330 + maybe CHEM 252 | Tier 3 needs both; Tier 4 may need 2 semesters of Organic |
| Mix of Tier 1 + Tier 4 | CHEM 251 + CHEM 330 | Substitution rarely accepted in either direction — take both |
| THE PRACTICAL DEFAULTFor applicants who haven’t yet figured out their tier mix and want the safest single course recommendation: take CHEM 330 Biochemistry I. Biochem clears Tier 1 programs and counts as the ‘either’ option at Tier 2 programs. The only major target lists where Biochem alone fails are pure Tier 3 (need to add Organic) and pure Tier 4 (Biochem not accepted at all). Biochem is the higher-value first move for the majority of applicants. |
Beyond the requirements question, applicants reasonably want to know what they’re signing up for. Organic Chemistry and Biochemistry cover overlapping but distinct material.
Biochemistry. By a clear margin. The metabolic pathways, enzyme kinetics, and macromolecule biochemistry that PA programs cover in pharmacology, pathophysiology, and clinical biochemistry modules draw directly from biochemistry. Organic Chemistry’s reaction mechanism content has its place — particularly in understanding pharmacokinetics and drug metabolism — but it’s less immediately relevant to PA school’s day-to-day curriculum than Biochem is. This is one reason the field has trended toward requiring Biochemistry.
A persistent applicant question: “Can I take Biochemistry instead of Organic Chemistry?” or vice versa. The answer at most CASPA programs is no.
Programs that name a specific course in their prerequisite list usually mean it. Duke states it directly: “We are not able to substitute Biochem for Organic Chem.” Programs in Tier 1 that require Biochemistry specifically generally do not accept Organic Chemistry as a substitute — because the clinical content they care about lives in Biochem, not in Orgo. Programs in Tier 4 that require Organic specifically generally do not accept Biochem because they care about reaction-mechanism reasoning.
A few programs explicitly allow the substitution. Kansas State’s PA program (which requires two semesters of General Chemistry) lets the second semester be substituted with Biochemistry or Organic Chemistry — treating them as interchangeable advanced chemistry options. Some Tier 2 programs accept either course as a substitute for the other within the prerequisite slot. But these are exceptions; the default is that programs mean what they list.
| COMBINED COURSES RARELY COUNTSome institutions offer combined courses titled ‘Bio-Organic Chemistry’ or ‘Organic and Biological Chemistry’ that mix organic and biochem content in a single course. These combined courses are explicitly rejected at many programs — Case Western, NYIT, and ECU all state this in their published requirements. The reasoning: a combined course doesn’t go deep enough in either subject to satisfy a prerequisite that names one or the other. If you’ve already taken a combined course and any of your target programs are Tier 3 or strict Tier 2, plan to take at least one standalone course to clear the requirement. |
You’re starting from scratch. Sequence: CHEM 151 General Chemistry I → CHEM 152 General Chemistry II → CHEM 251 Organic Chemistry I → CHEM 330 Biochemistry I. Plan 12–18 months at a self-paced rate. Once you’ve built the foundation, you’ll have the prereqs for the strictest Tier 3 programs.
Add Biochemistry. Take CHEM 330. With Orgo I + Biochem I both on your transcript, you’ll satisfy Tier 1, Tier 2, and Tier 3 programs (the largest combined market). Tier 4 programs that want two semesters of Organic might still ask for CHEM 252 — verify each program individually.
Unusual but it happens — some biology programs let students substitute biochem for organic. If your target programs are Tier 1 or Tier 2, you’re fine. If any target programs are Tier 3 or Tier 4, you’ll need to add CHEM 251 Organic Chemistry I. This is one of the most common ‘I thought I was done with chemistry’ surprises.
You satisfy Tier 4 programs (Organic-only). For Tier 1 and Tier 3 programs that require Biochem, you’ll need CHEM 330. This is a frequent pattern for applicants from biology programs that historically required Organic but not Biochem.
Take CHEM 251 and CHEM 330 — at minimum. This pair clears Tiers 1, 2, and 3, and partially clears Tier 4. If any Tier 4 program requires two semesters of Organic, add CHEM 252. The two-course foundation (one Orgo, one Biochem) is the safest portfolio for an applicant casting a wide net.
Here’s how the realistic paths through this decision compare:
| Strategy | Total Cost (PrereqCourses) | Time (Self-Paced) | Tiers Cleared | Risk |
|---|---|---|---|---|
| Biochem only (CHEM 330) | $675 | 10–16 weeks | Tier 1, partial Tier 2 | Fails Tier 3 & 4 |
| Organic I only (CHEM 251) | $675 | 10–16 weeks | Tier 4, partial Tier 2 | Fails Tier 1 & 3 |
| Both (CHEM 251 + CHEM 330) | $1,350 | 16–24 weeks | Tiers 1, 2, 3, partial Tier 4 | Low risk |
| Two Organic semesters (251 + 252) | $1,350 | 16–24 weeks | Tier 4 in full | Fails Tier 1 & 3 |
| Full stack (251 + 252 + 330) | $2,025 | 24–36 weeks | All four tiers | Highest cost & time |
Both Organic Chemistry and Biochemistry fall under CASPA’s Chemistry course subject classification at most institutions. They count toward your science GPA, your BCP GPA (Biology, Chemistry, Physics), and your prerequisite GPA at programs that include them in the prereq list. Strong grades in either course improve the BCP GPA that competitive programs scrutinize most heavily.
FSU’s PA admissions page states explicitly that the admissions committee gives ‘particular attention to organic chemistry and biochemistry undergraduate courses’ when reviewing applications. Other programs apply similar informal weight even when they don’t state it. A B+ in either course signals one thing; a C signals another. The grade matters more than the course choice.
Most CASPA programs allow one or two prerequisites to be in-progress at submission. Biochemistry is the prerequisite most commonly left in-progress, simply because it sits at the end of the chemistry sequence. Plan to have Organic Chem I complete before submission; Biochem can typically be in-progress.
Biochemistry. It satisfies more PA programs than Organic alone (Tier 1 + partial Tier 2 vs. Tier 4 + partial Tier 2), it’s more clinically relevant, and it’s the direction the field is trending. The only reason to take Organic alone instead is if all your target programs are explicitly Tier 4.
Sometimes. Most regionally accredited Biochemistry courses (including CHEM 330) list Organic Chemistry I as a prerequisite to enrolling, because the molecular structure content of Organic is foundational to Biochem. At Upper Iowa University, CHEM 330 requires CHEM 251 as a prerequisite. If you don’t have Organic, you’ll need to take it before Biochem regardless of whether your PA target programs require Organic separately.
Usually no. Case Western, NYIT, and ECU explicitly reject combined courses. Some programs accept Bio-Organic Chemistry for the Organic prerequisite (if it’s structured as an Organic course with some biochem applications); few programs accept it for the Biochem prerequisite. Plan to take standalone courses.
Often yes for Organic; often no for Biochem. Most Tier 3 programs that require Organic Chemistry specify ‘with lab.’ Most programs that require Biochemistry don’t require a lab. This is one practical advantage of Biochem over Organic — the lab logistics are simpler for online learners.
Less often than you might think. Many CASPA programs that require Organic Chemistry require only Organic I. Tier 4 programs that historically required two semesters of Organic have largely shifted to a single semester. Verify each program — Organic II is required at a minority of CASPA programs.
A lot. FSU explicitly calls out grade attention in both courses. CASPA includes both in the BCP GPA that competitive programs look at. A strong grade in Biochem or Organic is the single most important data point you can add at this stage of your application.
The Orgo vs. Biochem question doesn’t have one answer — it has four. Once you’ve categorized your target programs into the four tiers, the course strategy follows directly.
| ENROLL NOWIf your target programs are Tier 1, 2, or 3, CHEM 330 Biochemistry I is the highest-value first move ($675, 10–16 weeks). If your target programs are Tier 3 or Tier 4, add CHEM 251 Organic Chemistry I ($675, 10–16 weeks). Both are 3-credit upper-division courses transcripted by Upper Iowa University, a regionally accredited four-year institution. Combined cost for both ($1,350) is dramatically lower than state university or post-baccalaureate equivalents. |
Enroll in CHEM 330 Biochemistry I | Enroll in CHEM 251 Organic Chemistry I | All PA prereq courses | Speak with an advisor
